DRY SEASON CONSERVATION AND MULTIPLICATION OF SWEET POTATO [IPOMOEA BATATAS (L) LAM.] PLANTING MATERIAL IN THE COASTAL SAVANNAH ZONE OF GHANA BY EM ELIA OBERYE MONNEY THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF M. Phil. DEGREE IN “CROP SCIENCE” DEPARTMENT OF CROP SCIENCE FACULTY OF AGRICULTURE UNIVERSITY OF GHANA LEGON MAY 2003 I hereby declare that this thesis is a product o f my own original work and has not been submitted to another university for the award o f a degree. Any help received in the compilation o f this thesis and all sources have been duly acknowledged. DECLARATION PROF. J. C. NORMAN (SUPERVISOR) DEDICATION To Kweku, my husband. ACKNOWLEDGEMENTS Many are those who have contributed in divers ways to make this thesis possible. I am grateful to all for the contributions made. While I cannot mention every one’s name here, it is important for me to acknowledge the contributions o f those without whose help this work would not have been possible. To the Lord my God who has brought me this far I bring all praise and adoration, and acknowledge that but for him, this work would not have been. I am most grateful to Dr. Francis Ofori, Director o f Crop Services for his support and encouragement, and to the Root and Tuber improvement Programme for providing the funds that made this work possible. My deepest appreciation goes to Prof. J. C. Norman, my supervisor for the comments, constructive criticisms and for reading through this thesis. And also to Prof. Essie Blay, Prof. Oduro, Dr. K Ofori and Dr, Kumagah of the Crop Science Department, and Dr. Wilson of the Zoology Department for their advice and helpful suggestions. My warmest appreciation is to Dr. Papanii Johnson, Dr. Vowortor and Mr. Noamesi o f the Food Research Institute, for reading through my proposals and helping with literature sources. I am also grateful particularly to Mr. Noamesi for granting me access to the improved storage bam used in the study. I am grateful to Mr. Tonyigah, Mr. Ankrah, Mr. Asante, and Mr. Adgyekum and all the other staff in the Department o f Crop Science and workers o f the University Farm, and to Larry my colleague. TABLE OF CONTENTS Page DECLARATION i DEDICATION ii ACKNOWLEDGEMENTS iii LIST OF TABLES vi LIST OF PLATES ix LIST OF FIGURES x ABSTRACT xi CHAPTER ONE INTRODUCTION 1 CHAPTER TWO LITERATURE REVIEW 4 CHAPTER THREE MATERIALS AND METHODS 28 CHAPTER FOUR RESULTS 40 CHAPTER FIVE DISCUSSION 83 CHAPTER SIX CONCLUSIONS 96 REFERENCES 99 APPENDICES 120 - v - LIST OF TABLES Table Title Page 1 Tubers and vines o f two sweet potato cultivars, Sauti and Okumkom 30 2 Percentage cuts and breakages in small unmarketable sweet potato tubers at the 32 start o f storage. 3 Mean Monthly Temperature (°C) and relative humidity (%) o f bam and the 33 atmosphere 4 Percentage weight loss in sweet potato tubers stored in improved bam. 40 5 Percentage shriveling o f sweet potato cultivars in improved bam. 41 6 Percentage rot in sweet potato tubers in improved bam. 46 7 Percentage sprouting in sweet potato tubers in improved bam. 47 8 Percentage insect damage in sweet potato tubers stored in improved bam. 47 9 Percentage tuber loss in sweet potato tubers stored in improved bam. 48 10 Number o f tubers o f two sweet potato cultivars planted in nursery. 49 11 Number o f days to fifty percent sprouting in tubers o f sweet potato cultivars stored 50 in improved bam and planted in nursery. 12 Number o f days to first vine harvest in tubers o f sweet potato cultivars stored in 51 improved bam and planted in nursery. 13 Number o f plants at first vine harvest in tubers o f sweet potato cultivars stored in 52 improved bam and planted in nursery. 14 Number o f plants with vines longer than 30cm at harvest in sweet potato tubers; 53 Sauti and Okumkom stored in improved bam and planted in nursery. 15 Effect o f storage period o f tubers on the initial mean leaf, stem and total dry weight 54 (g) of sweet potato vines at harvest 16 Total number o f harvests in tubers o f sweet potato stored in improved bam and 56 planted in nursery. - vi - 17 Total number o f vines harvested per plot in tubers o f sweet potato stored in improved bam and planted in nursery. 18 Effect of tuber storage period on percent vine production in sweet potato cultivars - Final Harvest. 19 Effect of tuber storage period on mean dry weight (g) in sweet potato cultivars- Final Harvest. 20 Effect of spacing o f sweet potato tubers on the rate of increase in the number of vines longer than 30cm produced 47 days after planting 21 Effect o f spacing o f sweet potato tubers on the rate o f increase in the number of vines longer than 30cm produced 62 days after planting. 22 Effect o f spacing o f sweet potato tubers on the rate o f increase in the number of vines longer than 30cm produced 70 days after planting 23 Effect of spacing o f sweet potato tubers on the rate o f increase in the number of vines longer than 30cm produced 77 days after planting 24 Effect of spacing o f tubers on vine production in sweet potato cultivars on the total number of plants harvested per plot 25 Effect of spacing o f tubers on vine production in sweet potato cultivars on the number o f apical vines harvested per plot 26 Effect o f spacing o f tubers on vine production in sweet potato cultivars on the number of middle vines harvested per plot 27 Effect of spacing o f tubers on vine production in sweet potato cultivars on the number of basal vines harvested per plot 28 Effect of spacing on the percent (%)vine production in sweet potato cultivars. 29 Effect o f spacing o f tubers on mean dry weight o f sweet potato cultivars at harvest 30 Effect of time o f initiation of vine multiplication on the initial number o f plants harvested in sweet potato cultivars nurtured in nursery 31 Effect o f time o f initiation of vine multiplication on the initial number o f 30cm vines harvested in sweet potato cultivars nurtured in nursery 32 Effect of time o f initiation of vine multiplication on initial mean leaf dry matter production in sweet potato cultivars - vii - 57 59 60 63 63 63 64 64 65 65 66 66 67 68 69 71 33 Effect o f time o f initiation of vine multiplication on initial mean stem dry matter production in sweet potato cultivars. 34 Effect o f time o f initiation o f vine multiplication on initial mean total dry matter production in sweet potato cultivars. 35 Effect o f time o f initiation of vine multiplication on number o f apical vines produced in sweet potato cultivars nurtured in the nursery. 36 Effect o f time of initiation o f vine multiplication on number o f middle vines produced in sweet potato cultivars. 37 Effect o f time o f initiation o f vine multiplication on number o f basal vines produced in sweet potato cultivars. 38 Effect o f time o f initiation o f vine multiplication on percentage apical vine production in sweet potato cultivars 39 Effect o f time o f initiation o f vine multiplication on percentage middle vine production in sweet potato cultivars 40 Effect o f time o f initiation o f vine multiplication on percentage basal vine production in sweet potato cultivars 41 Effect of early initiation o f vine multiplication on the final mean leaf dry weight in sweet potato cultivars nurtured in the nursery. 42 Effect o f early initiation of vine multiplication on the final mean leaf dry weight in sweet potato cultivars nurtured in the nursery. 43 Effect of early initiation of vine multiplication on the final mean stem dry weight in sweet potato cultivars nurtured in the nursery. 71 72 73 74 75 77 78 79 80 81 82 - viii - LIST OF PLATES Plate Title Page 1 Improved storage bam with thatch. 34 2 Tubers randomly placed on shelves with thermo-hydrograph. 34 3 Some Sauti tubers with signs of rotting five weeks after storage. 42 4 Some Okumkom tubers with signs o f rotting five weeks after storage. 42 5 Some Sauti tubers with signs of rotting fifteen weeks after storage. 43 6 Some Okumkom tubers with signs o f rotting fifteen weeks after storage. 43 Sprouting in tubers o f Sauti (a) and Okumkom (b) five weeks after storage. 44 8 Sprouting in Sauti sweet potato tubers fifteen weeks after storage. 45 9 Sprouting in Okumkom sweet potato tubers fifteen weeks after storage. 45 - ix - 49 50 51 55 55 58 62 62 62 65 70 76 LIST OF FIGURES Title Interaction effect o f storage period and sweet potato tubers on the rate o f insect damage in tubers. Interaction effect o f storage period and sweet potato tubers on the rate o f tuber loss. Interaction effect o f storage period and sweet potato cultivars on available tubers for planting. Effect o f storage period on the number of 30cm vines produced in sweet potato cultivars at first harvest. Interaction effect o f storage period on the number o f apical vines produced in sweet potato cultivars. Effect o f storage period on the total number o f 30cm long vines produced in sweet potato cultivars Rate of sprouting in sweet potato tubers planted at 25cm x 10cm Rate o f sprouting in sweet potato tubers planted at 25cm x 15cm. Rate o f sprouting in sweet potato tubers planted at 25cm x 20cm Effect of spacing on the total number of 30cm long vines produced in sweet potato cultivars. Effect o f time o f early initiation o f vine multiplication on the total number o f 30cm vines produced in sweet potato cultivars. Effect o f harvest time on the total number o f 30cm long vines produced in sweet potato cultivars at final harvest. - x - ABSTRACT Three experiments were conducted during the dry season from October 2001 to April 2002 at the University o f Ghana Farms and the Food Research Institute, to evaluate two methods of conservation o f sweet potato planting material and one method of multiplication o f vines were evaluated in this study using two cultivars - Sauti and Okumkom released to farmers by the Crops Research Institute. The study was aimed at developing a technology to ensure the availability o f adequate quantities o f sweet potato planting material at the beginning of the planting season. In Experiment 1, small unmarketable tubers were stored in an improved bam for 0, 5, 10 and 15 weeks and then planted in the nursery. Sprouts from tubers planted were used to generate planting material for field planting o f sweet potatoes. In Experiment 2, small unmarketable tubers o f two sweet potato cultivars, Sauti and Okumkom, were planted at three different planting distances; 25cm x 10cm, 25cm x 15cm and 25cm x 20cm and evaluated for their vine yields. In Experiment 3 the effect o f the conservation o f vines of Sauti and Okumkom in the nursery and early initiation o f vine multiplication were evaluated. Except for sweet potato weevil (Cylas puncticollis (Sum) ) damage in tubers in which significant differences (P=0.05) were observed between the cultivars, results obtained from storage o f tubers showed that differences between the cultivars were not significant for percentage weight loss, percentage shriveling, percentage sprouting and percentage rotting. However, for the different periods o f storage, the percentage weight loss, - xi - percentage shriveling, percentage rotting, percentage insect damage and percentage sprouting increased significantly with increased period o f storage. The resultant number o f 30 cm apical, middle basal and total number o f 30cm vines obtained from the remaining tubers planted, decreased significantly with increase in storage period. Although differences observed among the different planting distances studied were not significant at P=0.05, planting both cultivars at 25cm x 15cm gave the highest number of planting material followed by 25cm x 10cm and then 25cm x 20cm Early initiation o f multiplication of planting material after conservation o f vines in the field - 14 weeks before field planting, gave the highest number o f 30 cm apical, middle, basal and total vines available for field planting, followed by 10, 8, 6, 4, and 0 weeks in decreasing order. Differences observed were significant at P=0.05. CHAPTER ONE 1.0 INTRODUCTION Sweet potato (Ipomoea batatas [L]) is grown throughout the tropics for the tubers (an important source o f carbohydrate) that are usually eaten boiled or baked, or used as a raw material in the starch, alcohol, carotene-juice, glue, and syrup industries. The tender tops and leaves are used as a pot-herb and the vines are widely used as a fodder for livestock. (Setijati et al. 1981; Purseglove, 1968; Onwueme and Sinha, 1991; Chukwu, 1995). The crop has a tremendous potential to be an efficient and economic source o f food energy (Ambe, 1997). It has a relatively short growing season and a wide adaptability to different agro-ecologies (Hahn, 1977 and Ambe, 1997). In Ghana, sweet potato cultivation and utilization is very prominent particularly in the savannah agro-ecologies (with an average annual rainfall o f between 700-900 mm and a long dry season of up to about six months from November to April) where it is produced both as a food and cash crop (Missah and Kissiedu, 1994). There is also the potential for increased production both as food and animal feed in the other agro-ecologies (Otoo et al., 1998). Recent market surveys have indicated an opening for the crop on the international market. In the year 2000, 6.873 tons o f the tubers amounting to $8,534 were exported to Europe. This increased in the year 2001 to 24,244 tons amounting to $12,396 - GEPC (2002). l Although yields o f up to 40 tons per hectare have been reported (Missah and Kissiedu, 1994), Otoo el al., (1998) indicated that yields obtained by farmers tend to be low and the quality reduced due to the low genetic potential o f varieties, diseases (fungal and viral) and pests (Cylas sp. and Acidodes sp.) infestations. There is also little or no information on appropriate agronomic practices and increased production is further limited by the availability o f planting materials (Okoli, 1988; Carey et al., 1997; Kakraba, 2001; Yankey, 2001). Sweet potato vines do not store for more than seven days (Okoli 1988). Onwueme and Sinha (1991) and Otoo (1998), reported that there is always a shortage o f planting materials at the beginning o f the farming season because, during the long dry season preceding the growing season the vines dry up. Sometimes, farmers are able to save only a small quantity o f planting material for the following season by planting a few vines in backyard gardens, dam sites, valley bottoms and the banks o f rivers. This practice restricts the expansion o f small farms, large-scale cultivation and the establishment of new fields (Okoli, 1988; Otoo, 1998; Kakraba, 2001; Yankey, 2001). It is therefore important to conserve planting material during the dry season, and special arrangements made to provide planting materials for sweet potato, which is harvested at a time when a new crop is not being planted (Okoli, 1988). The Crops Research Institute of the Council for Scientific and Industrial Research in Ghana is promoting the use of the rapid vine multiplication technique, to produce vine 2 cuttings for planting by farmers. Farmers using this technique, plant available vines at 10cm x 10cm intervals in the nursery at the onset o f the rains, apply nitrogen fertilizer and harvest vines for planting five weeks after nursing. Apart from this not much work has been done on the conservation and multiplication o f planting materials for the crop - (CRI, 2000). This study therefore aims at developing a technique that would ensure the availability of adequate quantities of sweet potato planting materials at the beginning o f the planting season for both local and export farmers. The objectives o f the study were to determine the: • Possibility of, and the optimum time for storing unmarketable sweet potato tubers in an improved bam for the early part o f the dry season and using them to generate planting material for the planting season. • Optimum spacing for tubers planted in the nursery. • Optimal time for maintaining sweet potato vines in mulched nursery beds prior to the initiation o f their multiplication for planting material production. • Yield o f planting material produced from tubers and vines after different periods o f storage during the dry season. 3 CHAPTER TWO 2.0 LITERATURE REVIEW 2.1. Origin and Distribution The Sweet potato - Ipomoea batatas (L) Lam o f the family Convolvulaceae is native to Central America (Hahn, 1977; Ambe, 1997), although it has been cultivated throughout the warm islands o f the Pacific Ocean for an equally long time (Sowley, 1999). It ranks seventh in total production among the world’s food crops (Opena et al., 1989), and is grown in areas reaching 40°N and 40°S latitudes and as high as 2000 m above sea level (Hahn, 1977) in more than 100 countries. Among the world’s root crops, it is second only to white potato (Solarium tuberosum) in importance (Horton, 1989). World production in 2001 was 135,918,673 metric tons o f which 10,203,169 metric tons was produced in Africa and 90,000 metric tons produced in Ghana (FAO, 2001). Roughly 80% of the world’s production is grown in Asia and just under 15% in Africa with only about 5% grown in the rest of the world. Developing countries grow nearly all the world’s sweet potatoes. China alone accounts for about 80% and also has much higher yields and production per head (Horton, 1989). The largest producing countries in Africa are Rwanda and Uganda. In West Africa, it is important in Liberia and Sierra Leone (Otoo et al., 1998) Its introduction to Ghana (Gold Coast) is believed to have been in the second half o f the 17th century (M.O.A., 1988). 4 2.2 Botany Setijati et al., (1981); Cobley and Steele, (1983); and Purseglove (1987) describe the sweet potato as a self incompatible, short day, dicotyledonous perennial herb cultivated as an annual with trailing or twining stems 1 -5 m in length with latex in all its parts. The stems are mainly prostrate, sometimes twining and light green to purple. The leaves are spirally arranged and either simple or deeply lobed. They are up to 15 cm long with pointed tips and may be green to purple. The root system is extensive and roots grow from the stem nodes where stems contact the soil. Tuber structure is mainly globular and smooth or ridged. The tuber surface may be white, yellow, orange, purple or brown and the flesh is white, yellow, orange, red or purple. The flowers may be single or in clusters (cymes); the calyx is five lobed, the corolla is funnel shaped or tubular and the petals are purple with pale margins. 2.3. Sweet Potato Propagation Sweet potato is clonally propagated as well as by seed. Sexual multiplication is exclusively reserved for the production of new cultivars (Cobley and Steele, 1983; Sihachakr et al., 1997; Daisy, 1998). Cuttings o f stem fragments 20-25cm long with 3-5 nodes are traditionally planted in family farms while roots bearing numerous adventitious buds are used as clonal propagation for commercial production (Sihachakr et al., 1997). Between 400,000 and 1,250,000 vines are planted per hectare depending on the cultivar (Du Plooy et al., 1988). 5 Planting materials usually consist o f sprouts, vine cuttings or root cuttings. Sprouts are produced by placing “seed roots” in beds (often later covered with sash or polythene film), covering the roots with 5-8 cm o f sand, then pulling the sprouts when they reach a height o f 20-25 cm. Vine cuttings, obtained from established plantings or nursery gardens are used primarily for production o f disease-free seed, or for main crop production in areas with long growing seasons (Bouwkamp, 1982; M.O.A., 1988; Gibson et al., 1997; Hoa, 1998; Sihachakr et al., 1997; Nair, 2000). Root cuttings are taken from secondary rather than main roots and should have up to six nodes per cutting. According to Du Plooy et al., (1988), the sweet potato is propagated by means o f vines cut into 30 to 40 cm slips. The authors stated that it is important to use healthy, insect- free propagation material since diseases and pests can be spread through propagation material. Long vines are cut into slips and divided into top or apical vines (growth point portions) and stem vines (rest o f the vine). The use o f planting material cut from the vines of old sweet potato lands should be avoided as these vines are usually from the voluntary growth of smaller and inferior sweet potatoes left in the ground after the crop was lifted. Moreover, this volunteer growth often arises from poor or diseased plants thus resulting in the continual selection o f poor planting material. Three types o f transplants: sprouts, cut sprouts and vine cuttings are normally used in the sub-tropical and warm temperate areas (Edmond, 1971a; Daisy, 1998). 6 Sprouts: these are entire plants, which arise and are pulled from the bedded roots. At the time they are ready for pulling, the above ground portion o f the stems is 15-20cm, has 4-6 physiologically active leaves, and an underground portion with a developed extensive root system. Although they require somewhat shorter time for their development than do cut-sprouts and vine cuttings, their main disadvantage is that sprouts spread Fusarium wilt, black rot and soil rot or scurf from infected soils to the field. Cut sprouts are essentially the above ground portions o f sprouts. The stems o f individual plants are cut usually at or just below the level o f the bedding media when the aboveground portion is about 18-25cm long. Vine cuttings are the terminal portions of plants growing in the plant bed or in the field. Usually, the stems are cut at the fifth or sixth node back from the terminal. In general, vine cuttings are used for the establishment o f new plantings in tropical and subtropical regions, and in warm temperate regions adjacent to subtropical regions (Edmond, 1971). Nair et al., (1989) reported that in India, sweet potato is propagated through vine cuttings obtained from either freshly harvested plants or a nursery. In Indonesia, farmers meet their planting material needs by taking apical vines from a previous crop or from stored roots (Jusuf et al., 1998). 2.3.1. Production of planting material: Different methods are employed in different countries in the production o f planting material. To obtain vine cuttings, Indian farmers raise nurseries either from healthy tubers 7 or from selected vines. Vines obtained from nurseries are healthy and vigorous resulting in maximum tuber production (Nair et al., 1989). In North Carolina, U.S.A., transplants are produced by pre-sprouting seed stock (roots) at curing temperatures (30°C) for approximately 4 weeks after a period o f storage dependent on the cultivar (some cultivars stored longer than others). The transplants are pulled and planted out, or where disease infestation is suspected, sprouts are cut off above the ground to avoid transmitting diseases onto the field (Wilson et al., 1992). Rice et al., (1991) and Alvarez, (1992) observed that in general, optimal use o f healthy good quality planting material in Africa is rare due to the lack o f adequate quantities when it is most needed. Seedlings vary in performance, and propagation from tubers and tuber shoots is also rare. Stem cuttings are most frequently used. Akoroda et al., (1992) listed a number o f methods employed by Cameroonian farmers to conserve planting material during the dry season, and generate material for planting at the beginning o f the season. These were 1. Harvesting vines from re-growth of un-harvested small tubers from previous farms. However, because o f slow re-growth, farmers have to wait until after two months o f rain before enough vines become available. 2. Vines cut from the main crop a few weeks before the end o f the seasonal rains are planted in a nursery by a stream, watered as and when necessary, and cut for planting at the start o f the rains. 3. Soon after harvest small unmarketable tubers are planted densely in nursery beds and mulched lightly. This method produces a lot o f vines that are cut for planting at the onset o f the rains. 4. Ridges and beds o f vines or tubercles are established under bananas or sugarcane in sites near streams or wetlands. These give reliable amounts o f planting material depending on the7 water regime, soil fertility, and field maintenance to control shading from other crops. 5. Beds o f small tubers are prepared, and over these, shelters are constructed with stick supports and grass thatch. Watering is highly regulated to control vine growth. 6. A large bunch o f old vines from the harvested field is kept near a stream or in a wetland and protected against animals. They concluded that adoption o f methods 2,3,4, or 5 was adequate for conserving planting material, but the use o f small tubers and vines was better. In East Africa, villagers typically leave some roots in the ground during the dry season, and months later, when the rains start, the roots re-sprouted and after a few weeks the vines are strong enough for farmers to take cuttings that they use to re-establish the crop. However, an early cessation and late on-set of rains in 1997 resulted in a six-month long drought which killed off most o f the plants. To prevent a recurrence o f another production crisis, healthy cuttings were planted in small 1.5 square meter beds in advance and watered as needed throughout the dry season. Cuttings were taken from these vines immediately the rains started without waiting for old roots to re-sprout. The added 9 advantage o f this method was that with cuttings from such a nursery, farmers begun the season with fresh clean planting material less likely to be infested with weevils (CIP, 1998). O f all the different types o f planting material used in sweet potato production, the tender apical vines have been found to give the highest planting material and tuber yields followed by the older woody vines, then the tubers. Nair, (2000) and Nair et al. (1989) indicated that use o f terminal vine cuttings had given the highest tuber yields at the Central Tuber Crops Research Institute. Hossain and Mondal (1994) and Hoa (1998) also reported that apical vines gave significantly higher tuber yields than middle and basal vines. Although middle vines gave higher yields than basal vines, the differences were not significant. Du Plooy et al., (1988) and Onwueme and Sinha (1991), reported that the top 30 cm vines produced higher yields than the stem vines, probably because the former have a better percentage take. Since only one top vine can be cut from each vine, top vines are fairly scarce and therefore more expensive. Plooy et al., (1992) further showed that the same potential existed for storage root formation in apical vines o f six different cultivars of sweet potato planted vertically or horizontally with 3-5 nodes beneath the soil surface provided that the planting material had been cut in between two nodes. 10 Ravindran and Mohankumar, (1989) found out that planting sweet potato vines after keeping under shaded conditions for two days gave the highest percentage yield followed by vines kept under shade for four days and freshly cut vines. They also reported that vine cuttings with leaves intact prior to planting had better establishment, sprouting and higher tuber yield than those without leaves. Hoa (1998) supported this when he reported that fresh undefoliated cuttings produced higher yields than defoliated or wilted cuttings. A vine length o f 20-40 cm was found to be optimum for tuber production. 2.3.2. Plant Tissue Culture: Progress has been made in the improvement o f sweet potato by using conventional breeding methods for the transfer o f resistance to diseases, nematodes and insects and also for increasing protein content and nutritional quality. Nevertheless, the selection process is time consuming and requires a high number o f individuals and improved breeding systems (Sihachakr et al., 1997). Fuglie et al. (1999) stated that sweet potato yields were significantly reduced due to diseases and pests in the planting material. The development and transfer o f new methods and technologies for producing clonal seed could overcome these constraints and help unlock the significant yield potential o f the crop. One o f such techniques is the use o f the tissue culture technique to supplement and complement conventional breeding methods and also to clean up sweet potato o f viral diseases that account for the crop producing well below its potential. 11 Some successes have already been made in the conservation and multiplication of planting materials using this technique. Dodds (1989) reported that it is possible to regenerate de novo in vitro plantlets from almost all plant parts when placed into culture. He further reported that several scientists have successfully regenerated plantlets o f sweet potato from cultured stems, petioles, roots and leaf discs. In all cases the first step is the formation of callus at the cut surface. Martin (1982) reported that callusing and rooting occurred rapidly when young but nearly foil sized leaves o f sweet potato were planted in sterile sand covered with a transparent chamber and partially shaded. Rooted leaves showed unusual growth phenomena including leaf enlargement, petiole swelling and storage roots that may sprout and generate normal plants. Schultheis et al., (1994) reported that vegetative growth, larger- sized storage roots (6cm in diameter), and total yields were consistently reduced when plants were derived from somatic embryos compared with propagules from stock plant origin. Kozai et al., (1998) reported that leafy node or shoot cuttings from disease- indexed, micro-propagated plantlets are widely used for vegetative propagation and transplant production o f sweet potato under natural light in the greenhouse in Japan. Nelson and Mantel (1989) demonstrated that micro-propagated plantlets o f sweet potatoes could be rapidly established in the nutrient film technique system, and concluded that large quantities of vigorously growing stem cuttings could be produced throughout the year to provide disease-free planting material, particularly for sweet 12 potato stock and cultivar introduction programs. Silva et al., (1991) also reported yield increases in tuber production when six different sweet potato cultivars grown from stem culture were compared with the same cultivars produced by traditional field multiplication methods. Vine yield and commercial class tubers were also greater with planting material derived from stem culture. When sweet potato production from true seed culture was compared with production from stem cuttings, Iwama et al., (1990) reported that with cultural practices that improved early top growth, crops grown from true seeds could yield as well as those conventionally grown from cuttings. Increasing the plant density in field plantings of cultivars raised in-vitro from 20 plants/m2 (0.25 x 0.2m), 36 plants/m2 (0.15 x 0.15m) and 54 plants/m2 (0.15 x 0.12m) resulted in increases in tuber numbers but decreases in tuber weight per m2 (Ekanayake et al., 1990). Wang et al., (1990) reported that virus-free sweet potato planting material had better dry matter accumulation when compared to controls and could be used extensively in sweet potato production. Although most o f these findings are still at the research level, China has moved further by using the virus clean up technique to produce disease free plants which are regenerated in greenhouses where they form small roots used to grow virus-free vine cuttings for farmers’ use (Fuglie et al., 1999). 13 2.4. Storage of sweet potato tubers Du Plooy et al., (1988) stated that a number o f practices must be followed to multiply sweet potato vines. The practice followed would be mainly determined by the climatic conditions in which the multiplication is to be done. As already stated, sweet potato tubers are also used for propagation either by direct planting or by using the tubers to produce sprouts or vines as planting material. Where the tubers are not immediately planted after harvest, i.e., in the temperate regions and regions with long dry seasons, it becomes necessary for the tubers to be stored for a while. However, in contrast to cereals, which have good natural properties for making them suitable for storage, sweet potato like other tropical roots and tubers is a perishable crop. The factors determining the storage properties o f tropical roots and tubers include high moisture content, mostly between 50-80%, and high to very high respiratory activity o f stored crops (Knoth, 1993). In temperate countries, sweet potatoes are usually stored in cold storage rooms where the temperature and relative humidity are controlled. Optimum storage conditions reported by Data et al., (1989) and Onwueme and Sinha (1991) are 15°C and 85-90% RH. Below this, chilling injury, decay, internal breakdown and impaired edibility may occur because lower temperatures favour the growth o f fungi that cause decay in sweet potato. On the other hand temperatures above 15.5°C reportedly shortens the storage life of sweet potato because it causes considerable weight loss. Dry matter content o f sweet potatoes 14 generally decreases during storage. The decrease is generally higher at 18.5°C than at lower temperatures and is attributed to the increase in respiration rate as manifested by increased moisture loss o f sweet potatoes stored at higher temperatures. Sowa (2000) reported that in the production o f planting material using tubers, storing tubers at 14°C and 90% RH delayed emergence o f seed potatoes and increased number of stems per plant. Gasiorowska and Zarzecka (2000) reported reduction in storage losses when maleic hydrazide was applied at 5kg/ha in 4001 o f water to potato tubers stored in cellars and clamps. The lowest losses were recorded when the inhibitor was applied four weeks before tuber harvest. In tropical countries, cold storage for sweet potatoes is not economically feasible. Hence researchers have studied different methods o f maintaining high relative humidity and low temperature conditions during storage. Kamalam, et al., (1998) reported that keeping the tubers in wooden boxes in layers with sand was effective in controlling storage pests and post-harvest deterioration for up to two months and beyond. Storage o f fresh tubers in moist sawdust, sand, and under ambient conditions have been studied, and results have shown weight losses o f 11.4, 9.88 and 40.71% respectively after 6 weeks o f storage (Data et al., 1989). Roots stored in sand and moist sawdust were still acceptable after six weeks o f storage while those stored at ambient conditions were no longer marketable. Storage in this system must however not last longer than the 15 dormancy period o f sweet potato after which sprouting and rotting may take place because o f the high relative humidity (Data et al., 1989). Sowley (1999) reported fresh weight losses of up to 22.69% in sweet potatoes stored for 8 weeks in storage bam. Clamp and pit storage have also been studied and recommended for use in some countries like Uganda, Tanzania and Philippines. In Uganda, research has shown that it is possible to keep tubers in good condition for as long as five months during the dry season (Data et al., 1989). In certain areas o f India, farmers store tubers in pits, sand beds, earthen pots or in heaps and covered with paddy straw or dry grass (Kamalam et al., 1998). According to Data et al., (1989), other village level storage structures with adequate ventilation, and temperatures and relative humidity lower than the outside have been developed in countries like the Philippines. Some o f these have additional slated walling to provide diffused light which inhibits sprouting to some extent. Care must however be taken to avoid over ventilation as it can result in excessive weight loss. Any storage structure designed for holding perishable produce at the rural level must afford protection from the prevailing weather conditions, allow adequate air circulation and ventilation and attain the lowest practical temperature (Bani and Josiah, 1995). Satish et al., (2000) observed shrinkage in 7-12 weeks o f storing potatoes and sprouting 3-8 weeks after storage when they tested four non-refrigerated storage methods i.e. passive- draft evaporatively cooled storage, radioactively cooled storage, farm level (brick and 16 sand) storage and evaporatively cooled storage. Assuming 10% total weight loss as the safe and economical limit, the potatoes could be stored for up to 10-13 weeks in non­ refrigerated storage structures while under ambient conditions potatoes can only be stored for up to 8 weeks. The condition o f the material before storage is one o f the most important factors governing the success o f the storage method used. Harvesting roots from flooded and/or cold soils adversely affected keeping quality and increased storage rots. Both conditions resulted in abnormal respiratory responses in roots tested (Ahn et al., 1980). To ensure good storage, only top quality roots free from insect damage, rots and rodent damage should be selected for storage. Varietal effects have also been recognized as important for the successful storage of sweet potatoes (Data et al., 1989). Wide varietal differences in weight loss were observed among sweet potato roots stored at 21°C. Variations were also observed in the ability of tubers to retain fresh quality during storage among different varieties used as parent material in developing new sweet potato genotypes). The storability o f roots was limited by the onset o f sprouting, greening, shriveling and susceptibility to decay causing pathogens. The effectiveness o f a storage method also depended to some extent on the variety owing to differences in susceptibility to diseases, length o f dormancy period, and transpiration 17 rate. Thus, the storage method for a variety with a potentially short shelf life may not be as effective when used for one with a longer shelf life (Data et al., 1989). In storage, sweet potatoes are subjected to several types o f post harvest losses like physiological damage, weight loss, pathological decay, sprouting, and sweet potato weevil infestations (Kamalam et al., 1998). Losses due to diseases, particularly soft rots can be very substantial. Soft rot, ring rot or collar rot caused by Rhizopus stolonifer is o f considerable economic importance. Under favourable conditions, it can destroy the entire tuber in a few days. Other storage rots and their causal organisms are Erwinia chrysanthemi, black rot {Ceratocystis fimbriata), surface rot (Fusarium oxysporum), dry rot (Diaporthe phaseolorum var batatatis), charcoal rot (Macrophomina phaseolina) and java black rot (Botryodiplodia theobromae), (Daisy, 1998; Sowley, 1999). B. theobromae has an optimum growth temperature o f about 28°C and is often a serious problem in the tropics. The sweet potato weevil, Cylas formicarius (Fab), is a major pest in most countries, where the larvae feed on the sweet potato roots in the field (Purseglove; 1987; Capinera; 1998). Another sweet potato weevil, C. puncticollis (Sum), is a serious pest on susceptible varieties planted in soils, which have previously carried infested crops. Exposed tubers or tubers near the soil surface are heavily attacked. The weevil attack is also serious during long periods o f drought (Sowley, 1999). Adult weevils feed on leaves and vines as well as on storage roots but the most severe damage is caused by the larvae 18 which tunnel the roots (Lema, 1992), and leave frass which render the fleshy roots unfit for food and feed (Edmond, 1971b). Early planting and harvesting greatly reduce weevil damage (Lema, 1992). To maximize yields and reduce pest damage, Missah and Kissiedu (1994) recommended that sweet potatoes should be harvested early; between three to five months after planting. Other practices like farm sanitation i.e. removal o f discarded and unharvested tubers and the destruction o f alternate hosts especially Ipomoea weeds are recommended (Capinera (1998)). Irradiation o f tubers prior to storage is also potentially effective in the control o f the insect although its older stages are less susceptible to destruction. Advanced technology improvements have been developed for the extension o f shelf life o f most agricultural produce. These include food irradiation, which is the process by which products are exposed to ionizing radiation to sterilize or kill insects and microbial pests by damaging their DNA (USEPA; 2002). Gamma irradiation is known to induce lesions on nucleic acids and cellular proteins thus preventing them from multiplying. In addition it inhibits sprouting in tubers, bulbs and root vegetables (USEPA; 2002). When applied at doses o f about 7.5 per head, gamma irradiation has been reported to inhibit sprouting of yams, potatoes and sweet potatoes. However, this technique has not yet been applied on a commercial scale in the tropics although it has been tested on yams where sprouting was inhibited for six months when tubers were irradiated before storage (Adesiyan; 1977; Diop 1998) 19 The effect o f irradiation on potato tuber yield and quality depended to a great extent on the physiological conditions o f the irradiated tubers in addition to the level o f irradiation dose (Avakyan et al.,; 1974). In addition to its effects on tuber yield and quality, Maghrabi and El-Sayed (1988) reported that gamma radiation inhibited sprouting of potato tubers in storage but, the incidence o f rotting during storage increased with increased dosage. Adesiyan (1977) reported that dosages o f 5 to 15krad o f gamma irradiation on yams entirely suppressed sprouting and signs o f deterioration but did not entirely eliminate nematodes. In stores using natural ventilation, with relatively high ambient temperatures (20°C to 30°C) such as are normally experienced in tropical and subtropical lowlands) and for any period o f storage beyond the normal or natural end o f the dormancy period, the use o f sprout inhibiting chemicals like CIPC (isopropyl-N-chlorophenylcarbamate) is the only practical means o f controlling sprouting. This treatment has proved effective on potatoes and sweet potatoes ( Diop, 1998). 2.4.1. Planting material production from tubers Yamashita (2000) studied the differences between propagation using lOg cut pieces of sweet potato roots treated with growth regulators and cut sprouts. Growth o f the transplants was vigorous with no transplanting injury after field planting. Plantlets nurtured for 50 days achieved the highest yield and best quality and did not show the thickening o f mother roots observed in direct planting using whole storage roots. 20 Pre-sprouting o f Georgia Jet Sweet Potato seed roots accelerated emergence from the plant bed and enhanced early, mid-season and total plant production. Small pre-sprouted roots produced as many as were produced by large pre-sprouted roots, or more than, early and mid-season plants. However, small pre-sprouted roots produced lighter weight plants. Cutting roots before bedding did not affect plant weight nor enhance early or mid-season plant production (Hall, 1986). Hall (1990) also reported earlier harvests and increases in total number o f plants produced from tubers immersed in ethephon before planting. Villamayor (1988) showed that the number o f accumulated cut sprouts increased linearly with number of days from planting. Slicing roots transversely in half reduced cut sprout production by 33% while application o f 30kg N or N, P and K each at 30kg/ha increased sprout production by 43 and 46% respectively. Cut sprouts and vine cuttings gave similar yields. Martin (1986) developed a technique for re-sprouting sweet potatoes for propagation purposes. Pieces o f or whole tubers were planted in a well drained growing medium in 6- inch plastic pots, thoroughly watered and maintained in the shade at temperatures o f 24- 28°C until several sprouts 10cm in length had been produced, and then moved into full sunlight. Fifteen centimeters long shoots were removed from plants for planting directly in the field or in containers. In trials with 17 sweet potato cultivars, sprouts were 21 produced in 7-18 days. A minimum of 14 sprouts was produced per pot in 30 days, and the number o f sprouts per pot ranged from 16 - 38 in 90 days. Mid-storage heating increased plant production from bedded sweet potato roots. Increasing the length o f time o f curing decreased emergence time and increased number o f early and mid-season plants produced, but had no effect on total number o f plants produced (Hall, 1993). Hall (1994) tested the elfects o f combined heating applications on the Red Jewel cultivar o f sweet potato seed tubers cured at 32° ±1°C and 85% RH for seven days immediately after harvest, and then subjected to additional curing before storage. The author reported that mid-storage heating or pre-sprouting, or a combination o f these treatments resulted in earlier emergence o f sprouts, and yielded more cumulative early, mid-season and total sprouts than non-heated tubers. The cost o f transplants is a major expense in the commercial production o f sweet potato. Sparse plant production from bedded roots o f some cultivars further increased propagation costs. Small roots produced more plants than large roots however small roots produced fewer plants per root. Pre-sprouting for three weeks or longer at 32° ± 1°C and 85%±5% RH promoted early plant production and an increased number o f plants from bedded roots (Hall, 1986). 22 2.4.2. Maintenance and multiplication of vines According to Lewthwaite and Triggs (1999), the amount o f planting material is limited in the early stages o f cultivar development. Wholey and Cook (1973) also stated that crop improvement programmes frequently encountered problems associated with the rate of multiplying planting material. A low rate o f planting material multiplication impeded agronomic testing o f new varieties, and delayed distribution to farmers. The problem was more acute with vegetatively propagated crops. It is important therefore that improvement programmes should have an organized procedure for rapidly multiplying improved cultivars. A successful programme must be able to multiply rapidly from an initial stock o f a small number o f plants. Lewthwaite (1999) and Lewthwaite and Triggs (1999) tested the use o f plug transplants which allow production o f robust and uniform plant stands from small amounts o f plant material, and reported that transplants held in air to allow root initiation suffered less transplant shock than those planted directly into the field, and concluded that for now, plug transplants may be useful for research purposes but are not recommended for general commercial use on the basis o f trials conducted. In order to ensure that high quality planting materials o f superior sweet potato varieties are available for farmers use at the beginning o f the planting season, Carey et al., (1997) multiplied pathogen tested in vitro cultures o f selected superior sweet potato varieties using 2-node cuttings in beds at a density o f 100 plants/m2. Depending on farmers’ 23 preferences, between 4,900 and 20,600 apical vines were harvested from the varieties and distributed to various locations to serve as nuclear stocks for subsequent multiplication and distribution to farmers. A study undertaken to examine differences in sprouting ability among International Potato Center bred clones showed significant cultivar variation in sprouting ability. In addition, clones found to produce the highest number of sprouts sprouted earliest. Another method used for plant material production in sweet potatoes is the topping of vines after crop establishment to promote branching (Hoa, 1998). Villamayor and Perez (1988) studied the effect o f topping on storage tuber and stem cutting production and reported that regardless o f the time o f topping, a single topping did not reduce total number, marketable and total tuber yield, herbage yield and harvest index. However, the number o f cuttings per plant increased with delay in date o f topping. Also, the number of cuttings/m2 depended on the stage o f sweet potato growth and increased with the frequency o f topping. The number o f total and marketable yield on the other hand decreased with increase in the frequency o f topping. Nakatani and Komeichi (1988) reported that the number o f roots decreased when cut sprouts o f sweet potatoes were held for 5-10 days under low light intensity at 16°C and 85% RH, and planted under soil conditions o f 30°C and 70% soil moisture. However, the elongation o f roots was accelerated and the length o f roots increased about 10% by holding. Rooting o f cut sprouts was restricted by low temperature or moisture. The 24 optimum soil temperatures for total root length o f 12 different cultivars o f sweet potatoes cuttings tested by Nakatani et al., (1989) under controlled environmental conditions ranged from 30-35°C. The application o f nitrogen fertilizer, the type o f planting material used, and the mode of planting and the kind o f substrate used to hold the planting materials have all been shown to affect the vine yield. Ruiz-Martinez et al., (1992) reported an increase in planting material production when 80kgN/ha and 2% foliar nitrogen was applied after each vine harvest for three consecutive harvests. The total yield o f 32.63t/ha fresh shoots obtained, represented an increase o f 34% over stands grown without nitrogen, and 20% over stands given a basal application o f 60kgN/ha and two applications o f 30kgN/ha as top-dressings. The depth o f ploughing, maturity o f cutting (apical, middle and basal vines) and planting method was found to affect tuber dry matter (Biswas and Singh; 1990). Sweet potato tuber starch and non-reducing, reducing and total sugar contents were highest in plants grown from apical vines in soil ploughed to a depth o f 20cm; while tuber dry matter percentage was highest from plants grown from apical cuttings in soil ploughed to 10cm depth. Nzima and Banga (1999), investigated inexpensive techniques o f maintaining and multiplying sweet potato vines during the dry season using three different cultivars grown on three different soils in three different types o f containers. Significant differences between the varieties and substrates tested, and different costs o f production for the different kinds of containers used were reported. 25 During establishment, drought significantly reduced the stem weight, and leaf weight and area, and similar but non-significant trends were also evident for root number and weight. Pardales et al., (2000) studied the effect o f fluctuations o f soil moisture on root development during the establishment o f sweet potato i.e. from planting to about one month. Findings from this study indicated that the number o f leaves, shoot dry weight and vine length were suppressed significantly by deficient moisture but were markedly increased by excessive moisture regardless of the time o f occurrence relative to the initial development o f the plant. However, Holwerda and Ekanayake (1991) reported that when drought stressed, a stem length o f 30cm with 10-15cm o f the stem covered by soil produced the most vigorous growth. The advantages o f dipping cuttings into a dissolved root hormone were cultivar dependent, but pre-rooted cuttings o f the two cultivars tested had no advantage in terms o f survival and growth. On the other hand, improving conditions for holding and handling sweet potato planting material prior to field planting increased availability o f planting material at planting. Bonte et al., (2000) evaluated the effect o f black polyethylene tunnel cover (BTC) on the quality and quantity o f transplants o f two sweet potato cultivars in plant beds and reported that the use o f BTC increased production o f transplants from 63% to 553% in one cultivar and 48% in the other in comparison with the bare ground control. Ahn et al., (2000) also studied the optimum conditions for over winter culture o f sweet potato stems to be used as transplant shoots instead o f sprouts produced in polyethylene film house 26 and reported that optimum conditions were mid October cutting time, planting density of 10 x 3cm and minimum maintenance temperature of 5°C. However, root yield produced by transplanted shoots from the stems was similar to the yield produced by shoots from roots. The survival rate was not different among varieties tested. 27 CHAPTER THREE 3.0 MATERIALS AND METHODS 3.1 Location of Experiment The study was conducted during the dry season from October 2001 to April 2002. The tubers were stored in an improved yam bam belonging to the Food Research Institute located at Taifa near Legon. The field study was carried out at the University o f Ghana Farm on the Haatso series o f soils (Brammer, 1967), which has been described as an entisol o f quartzipsamment (U. S. D. A., 1992). 3.2 Climatic data The climate under which the experiment was conducted is warm and dry Coastal Savanna with a mean annual rainfall o f 800mm and two growing seasons (100- 110 days and 50 days per year). The major growing season occurs between April and July while the minor season occurs between September and November (Walker 1957; Doku 1988 and MOA 1991). Five years (September - April 1996/97 to 2001/02) meteorological data for the period during which the experiment was carried out were taken and are presented in Appendices la-e. These data show the trend and give a history o f the prevailing conditions as well as an estimation o f what could be expected during the period o f planting material conservation at Legon where the experiment was conducted. 28 3.3 Soil sampling and analysis Before the establishment o f the experiments the soils samples were collected and analyzed to determine the nutrient status o f the field. 3.3.1. Soil sampling The soil sample was collected from the Ap horizon at a depth o f 0-15cm The topsoil of the soil profile consisted o f approximately 20cm o f pale brown sand with weak, fine granular structure and had a loose and friable consistence. It contained fine and abundant common medium roots. 3.3.2. Soil analysis The soil was analyzed to determine its nutrient levels by the following methods. (i) The Macro - Kjeldhal (AOAC, 1975) method that is essentially a wet oxidation procedure, was used for nitrogen determination. (ii)Total phosphorus and available phosphorus were determined using Bray and Kurtz (1945) method. (iii) Organic phosphorus and soluble phosphorus was determined using Saunders and Williams (1955) (a modified Bray No. 1) method. (iv) Flame photometry was used to determine potassium levels in the soil (Moss, 1961; Rayment and Higginson, 1992) after exchangeable cations (EC) or bases were determined using ammonium acetate (1.0MNH40AC) method at pH 7.0 29 (v) Organic carbon content was determined using Walkley and Black Procedure (Nelson and Sommers; 1982). The characteristics of the soil used in the study are as follows: the concentration of nitrogen was 0.084%, % phosphorus was 0.019, potassium was 0.48ppm, % organic carbon was 0.38 and % organic matter was 0.66. 3.4 Sweet potato cultivars Description o f the tubers and vines o f the two sweet potato cultivars used in the experiments are shown in Table 1. Table 1: Tubers and vines of two sweet potato cultivars, Sauti and Okumkom (after Otoo; 1998) Cultivar Pubescence Leaf Tuber Young leaves colour Leaf petiole colour Leaf vein colour (abaxial view) Leaf shape Tuber skin colour Tuber shape Protein content tuti Hairy at nodes Green Green Green Palmate Green Long irregular curved 5.3% protein kumkom (TIS :66) Profuse Green Green Green Cordate Light purple Round elliptical mixture 5.1% protein 30 (v) Organic carbon content was determined using Walkley and Black Procedure (Nelson and Sommers; 1982). The characteristics o f the soil used in the study are as follows: the concentration of nitrogen was 0.084%, % phosphorus was 0.019, potassium was 0.48ppm, % organic carbon was 0.38 and % organic matter was 0.66. 3.4 Sweet potato cultivars Description o f the tubers and vines o f the two sweet potato cultivars used in the experiments are shown in Table 1. Table 1: Tubers and vines of two sweet potato cultivars, Sauti and Okumkom (after Otoo; 1998) Cultivar Pubescence Leaf Tuber Young leaves colour Leaf petiole colour Leaf vein colour (abaxial view) Leaf shape Tuber skin colour Tuber shape Protein content Sauti Hairy at nodes Green Green Green Palmate Green Long irregular curved 5.3% protein Okumkom (IIS 8266) Profuse Green Green Green Cordate Light purple Round elliptical mixture 5.1% protein 30 tubers o f the Sauti (creamlike skinned) were long, irregular and curved. Not all the tubers were whole, some had been cut while the ends o f others had been broken during harvest; therefore, each treatment was assessed for breakages and cuts. Table 2 describes the state of the tubers at the beginning o f storage. Table 2: Percentage cuts and breakages in small unmarketable sweet potato tubers at the start of storage Sauti Okumkom Storage period (weeks) Storage period (weeks) 0 5 10 15 0 5 10 15 % Cuts 4.5 2.2 0 0 6.7 11.1 13.3 4.5 % Breakages 13.3 2.2 4.5 0 2.2 6.7 4.4 2.2 3.5.1.1. Description of Storage facility: A naturally ventilated, rodent-proof storage structure, 7.4m x 1.3m x 1.3m on 0.7m high supports, which was constructed with hardwood, and 5mm mesh expanded metal was used for storing the sweet potato tubers. The base served as a single 7.4m x 1.3m shelf for sweet potato tuber storage. The sides were hinged at the top and padlocks were fixed for security. The structure was roofed with thatch extending sufficiently over the sides to exclude direct sunshine from the shelf area. Plates 1 and 2 show pictures o f the bam and how tubers were randomly placed on the shelf. Shelf temperature and relative humidity were measured with a thermo-hydrograph. Table 3 represents temperature and relative humidity values recorded compared to the atmospheric values. 32 Table 3. Mean monthly temperature (°Q and relative humidity (% ) of bam and atmosphere Temperature (°Q Relative humidity (%) Barn Atmosphere Bam Atmosphere October 2001 28.9 27.4 75.5 81.5 November 2001 28.9 28.1 79.8 80.0 December 2001 28.3 28.3 78.0 81.0 January 2002 29.5 27.7 68.5 74.5 February 2002 29.0 28.9 79.6 74.5 March 2002 29.8 28.8 75.3 77.5 3.5.1.2 Data collection: Initial data collected were: • Initial average tuber weight = Total weight o f tubers No. o f tubers / treatment • Percentage breaks = No. o f broken tubers x 100 No. o f tubers / treatment • Percentage cuts = No. o f tubers with cuts x 100 Total no. o f tubers / treatment Data collected during storage at fortnightly intervals: Average tuber weight = Total weight o f tubers No. o f tubers / treatment • Average weight loss = Average tuber weight Average tuber weight. • % Tuber weight loss = 100 - average weight loss x hundred. 33 Plate 1: Improved storage bam with thatch. Plate 2 showing tubers randomly placed on shelves with thermo-hydrograph. 34 • % Shriveling = No. o f shriveled tubers x 100 Total number o f tubers / treatment • %Rotting = No. o f rotted tubers x 100. Total number o f tubers / treatment • % Sprouting = No. of tubers sprouted x 100 Total number o f tubers / treatment • % Insect damage = No. o f insect damaged tubers x 100 Total number o f tubers / treatment 3.5.1.3 Planting of whole tubers in nursery beds after storage After the set period o f storage for each treatment, the total number o f whole tubers remaining was noted and then planted in lm x 0.6m nursery ridges 30cm high, at the University o f Ghana Farms, Legon. The beds were mulched with dry bahama grass (Cynodon dactylori). Soil temperature and moisture were monitored three times a week. Except for rainy days, beds were irrigated three times a week to maintain soil moisture at field capacity. Soil moisture content was measured with a tensiometer and kept between 70-90%. Soil temperature was recorded with a thermometer and ranged between 29 - 32°C. 3.5.1.4 Harvesting and data analysis During the growing period, whenever 50% o f the vines measured 30cm above the first two nodes, they were cut, and the total number o f vines per plot recorded and replanted on different beds. Time to 50 % sprout, 50 % growth o f vines to 30cm beyond the first two nodes, leaf and stem dry weight at vine harvest were recorded. 35 The following parameters were also recorded: • Number o f 30 cm vines at each harvest • Total number o f vine harvests per treatment, • Average leaf and stem dry weight for five sample plants at each vine harvest • Total number o f vines at final harvest. • Percent apical, middle and basal vines at final harvest. • Cumulative number o f vines generated per treatment at the end o f the season The average leaf and stem dry weight for 5 plants per treatment were taken after being oven dried at 70°C for 72 hours. Data was analyzed using Statview statistical package. Data were subjected to Analysis of variance (ANOVA) and means separated at P < 0.05 by LSD. 3.5.2. Experiment 2: Effect of spacing on vine yield of two sweet potato cultivars. The design for the experiment was a 2 x 3 factorial in Randomized Complete Block Design. Two factors, i.e., cultivar and planting distances, were studied. Two cultivars - Okumkom and Sauti, and three planting distances 25 cm x 10 cm, 25 x 15 cm, and 25 cm x 20 cm Treatments were replicated four times. The tubers were planted on 28th November 2001 and harvested on 22nd April 2002. Tubers o f the two cultivars were planted on ridges (lm x 0.6m 30cm ) mulched with bahama grass (Cynodon dactylori) at three different planting distances 25cm x 10cm, 36 25cm x 15cm, and 25cm x 20cm, giving plant populations o f 400,000 plants/ha, 266,666 plants/ha and 200,000 plants/ha respectively. After sprouting, the vines were maintained until after the first rains at the beginning o f the planting season when the vines were then harvested. Time to 50% sprouting and the number o f 30cm length vines were recorded. The stem and leaf dry weights of five sample plants were recorded. Data were analyzed using Statview statistical package and the means separated at P < 0.05 by LSD. 3.5.3. Experiment 3: Effect of dry season field conservation and early initiation of planting material production in two sweet potato cultivars. This experiment studied the most suitable time to initiate multiplication o f vines in the nursery for field planting and the most suitable period for maintaining vines in the field. The experimental design was a 2 x 6 factorial in a Randomized Complete Block Design. Two factors were studied, i.e., cultivar and time for initiating vine multiplication. The cultivars were Okumkom and Sauti, and the time for initiating vine multiplication were 14, 10, 8, 6, 4 and Oweeks before field planting. The treatments were replicated three times. Vines o f the Sauti and Okumkom cultivars obtained from the Agricultural Research Station at Asuansi were planted on the 1st October 2001 at the University o f Ghana Farm, Legon. Two 30 cm vines per stand were planted at a spacing o f 40 x 40cm giving a population of 125,000 plants per ha. 36 beds (i.e. 2 cultivars x 6 treatments for time of 37 initiation o f vine multiplication and replicated 3 times) measuring 3m x 0.60m x 30cm high were used. The beds were mulched with bahama grass (Cynodon dactylori). Watering and weeding were done when necessary. Plants were sprayed with Cymethoate at 25ml/l two times during the experimental period to control grasshoppers. The time o f field planting was hypothetically set for the second week o f March 2002 when all vines in the plots were cut and counted. Final harvest was done on 13th March 2002. 3.5.5.1. Vine multiplication Fourteen weeks before the hypothetic date o f 13th March 2002, that is, on the 6th December 2001, vines o f the plots representing this treatment were harvested, cut into 30cm pieces, counted and replanted (Tl). • On 2nd January 2002, the plots representing vine initiation at ten weeks before field planting were harvested cut into 30cm pieces, counted and replanted (T2). • On 16th January 2002, those plots representing vine initiation at eight weeks before field planting were harvested cut into 30cm pieces, counted and replanted (T3). • The plots representing vine initiation at six weeks before field planting were harvested cut into 30cm pieces, counted and replanted on 30th January 2002 (T4). • Plots representing vine initiation at four weeks before field planting were harvested cut into 30cm pieces, counted and replanted on 13th February 2002 (T5). 38 • Plots representing no initial multiplication before field planting i.e. 0 weeks were harvested cut into 30cm pieces and counted on 13th March 2002 (T6). In between these harvests, anytime a plot had 50% of the vines longer than 30cm and two nodes, they were cut. The number o f 30cm vines produced per plot were counted and replanted. In all, T1 was harvested seven times. T2, T3, T4, and T5 were harvested three times and T6 once 3.5.3.1 Data collection The following data were collected; • Number o f 30cm vines harvested initially, • Average leaf and stem dry weight for five sample plants at each vine harvest • Number o f 30cm vines o f subsequent harvests times • Total number o f vines at final harvest. • The % apical, middle and basal vines at final harvest. • The cumulative number of vines generated per treatment by the end o f the season for each experiment. 3.5.3.2 Data analysis Data was analyzed using the StatView statistical package. Analysis o f variance (ANOVA) was based on 2 x 6 factorial randomized complete block design. 39 CHAPTER FOUR 4.0 RESULTS 4.1. EXPERIMENT 1: Effect of dry season storage of small unmarketable sweet potato tubers on planting material production of two sweet potato cultivars. 4.2.1 Tuber storage. 4.2.1.1. Effect of storage period on the percentage weight loss of sweet potato cultivars. Table 4 shows the percentage weight loss o f the sweet potato tubers stored for 0, 5, 10 and 15weeks. Percentage tuber weight loss increased significantly (P=0.05) with duration o f storage. With Sauti, the differences observed were significant for tubers stored for 0 week and those stored for 10 and 15 weeks. There were no significant differences between tubers stored for 0 and 5 weeks, 5 and 10 weeks and 10 and 15 weeks. On the other hand, in Okumkom, significant differences were observed between 0 week and 5, 10 and 15 weeks o f storage, but differences between 5,10 and 15 weeks were not significant. Even though numerical differences were also observed among the varieties tested, these were not statistically significant (P<0.05). Table 4. Percentage weight loss in sweet potato tubers stored in improved barn Weeks in storage Variety LSD(s%)Sauti Okumkom 0 0 0 23.5 5 22.0 26.5 10 24.9 28.1 15 27.7 40.4 LSD(5%) N.S. 40 4.1.1.2 Effect of storage period on percentage shriveling in sweet potato cultivars Shriveling was identified by dryness and wrinkling o f the skin o f tubers. Table 5 shows percentage shriveling in both cultivars. % Shriveling increased as duration o f storage increased, percentage shriveling also increased. Significant differences (P = 0.05) were observed between 0 week and 5, 10 and 15 weeks o f storage and between 5 and 15weeks, but differences between 5 and lOweeks o f storage were not significant at P=0.05. Differences observed between the cultivars were not significant. Table 5. Percentage shriveling of sweet potato cultivars in improved bam Weeks in storage Cultivar Sauti Okumkom LSD(s%) 0 0 0 19.6 5 55.5 65.6 10 66.8 66.7 15 84.0 88.9 l s d (5%) N.S. 4.1.1.3 Effect of storage period on percentage rot in sweet potato cultivars Apart from the tubers planted without prior storage (0 weeks) rotting was observed in all tubers stored before planting. Table 6 shows percentage tuber rot at the end o f storage for all the treatments. Significant differences (P = 0.05) were observed among storage 41 Plate 3: Sauti sweet potato tubers with signs o f rotting five weeks after storage. Plate 4: Okumkom sweet potato tubers with signs o f rotting five weeks after storage 42 Plate 5: Sauti sweet potato tubers with signs o f rotting fifteen weeks after storage. Plate 6: Okumkom sweet potato tubers with signs o f rotting fifteen weeks after storage. 43 (a) (b) Plate 7: Sprouting in tubers o f Sauti (a) and Okumkom (b) five weeks after storage. 44 Plate 8: Sprouting in Sauti sweet potato tubers fifteen weeks after storage. Plate 9: Sprouting in Okumkom sweet potato tubers fifteen weeks after storage. 45 periods with percentage rot increasing as storage period increased from 0 to 15 weeks. Differences between 0 week o f storage and for 5, 10 and 15 weeks were significant for Sauti. The differences between tubers stored for 5, 10 and 5 weeks were not significant. On the other hand, in Okumkom, significant differences were observed between 0 weeks and 5, 10 and 15 weeks o f storage, and 15 and 5 and 10 weeks o f storage. Differences between 5 and 10 weeks were not significant. The pathogen causing the rot was identified as Botryodiplodia theobromae. Differences observed among cultivars were not significant (P=0.05) Plates 3 and 4 show tubers with signs o f rotting five weeks after storage. Plates 5 and 6 show some o f the rotten tubers at 15 weeks after storage. Table 6. Percentage rot of sweet potato tubers in improved barn Weeks in storage Variety Sauti Okumkom LSDf5%) 0 0 0 16.6 5 26.7 22.2 10 34.9 37.2 15 34.8 58.3 LSD(s«/ol N.S. 4.1.1.4 Effect of storage period on percentage sprouting in sweet potato cultivars Generally, percentage sprouting increased with increased period o f storage. Results o f the analysis indicated that differences were significant at P = 0.05. Although sprouting had occurred in both cultivars by the 5th week o f storage, LSD values showed that differences between tubers stored and those not stored (which had no sprouts) were not significant (Table 7). Plates 7a and b shows sprouting in 46 tubers 5 weeks after storage, and Plates 8 and 9 show sprouting in tubers 15 weeks after storage. Table 7. Percentage sprouting in sweet potato tubers in improved barn Weeks in storage Cultivar Sauti Okumkom LSD(5»/o) 0 0 0 23.7 5 13.5 20.0 10 34.9 60.0 15 62.8 60.6 LSD(5%) N.S. 4.1.1.5.Effect of storage period on percentage insect damage in sweet potato cultivars The percent insect damage on the sweet potato tubers increased with increased period of storage with Sauti being more susceptible to insect damage than Okumkom (Table 8, Figure 1). Significant differences (P = 0.05) were observed between the different storage periods, and between the cultivars at 15 weeks o f storage. The main insect pest was identified as Cylas puncticollis (Sum). Other insects observed in the bam were identified as Araecerus fasciculatus (Deyeer) (Coleoptera: Anthribidae) and Lasioderma serricorne (Fabricius) (Coleoptera: Anobiidae). Table 8. Percentage insect damage in sweet potato tubers: Sauti and Okumkom stored in improved ham Weeks in storage Cultivar Sauti Okumkom l s d (5%) 0 0 0 5.5 5 2.2 2.2 10 7.9 6.7 15 42.8 12.2 LSD(5%) 7.7 47 4.1.1.6. Effect of storage period on percentage tuber loss in sweet potato cultivars Prior to field planting, the percentage o f tubers lost during storage for each cultivar was assessed. There was a significant increase with increased period o f storage (P=0.05). By the end o f the 5th week Sauti had lost significantly more tubers than Okumkom. Tuber losses in the 10th week were not different between the cultivars, but this changed again in the 15th week with Okumkom loosing more tubers than Sauti (Table 9). Significant differences (P = 0.05) were also observed between the interaction effect o f cultivar and period o f storage - Figures 2 and 3. Table 9. Percentage tuber loss of sweet potato cultivars stored in improved bam Weeks in storage Cultivar Sauti Okumkom LSD(So/o) 0 0 0 7.3 5 60.0 26.7 10 66.0 69.3 15 72.0 89.3 LSD(S%) N.S. 4.1.2 Nursery 4.1.2.1. First vine harvest from tubers planted after a period of storage 4.1.2.1.1. Effect of storage period on number of tubers of sweet potato cultivars planted Table 10 shows the number o f tubers planted in the nursery for each treatment after the set storage period. With respect to storage period, significant differences (P<0.05) were observed in the number o f tubers planted whereas differences observed between cultivars 48 were not significant at P=0.05. Figure 2 shows the interaction effect of storage period and cultivars stored. The interaction effect observed was significant (P=0.05) only at five weeks o f tuber storage. Table 10. Number of tubers of two sweet potato cultivars planted in nursery. Weeks in storage Cultivar Sauti Okumkom LSD(5%) 0 50.0 50.0 4.3 5 20.0 36.7 10 17.0 15.3 15 14.0 5.3 l sd (5%) N.S. Fig.1. Interacton effect of storage period and sweet potato tubers on the rate of insect damage in tubers T3 CD CD . ” g, CD U) oa) B. cn 60 50 40 30 20 10 0 - Sauti - Okumkom Storage period (weeks) 49 Fig.2: Interaction effect of storage period and sweet potato tubers on the rate of tuber loss Storage period (weeks) 4.1.2.1.2. Effect of storage period on the number of days to fifty percent sprouting in sweet potato cultivars The rate of sprouting o f the two sweet potato cultivars, Sauti and Okumkom, in the nursery increased as the storage period increased such that tubers not stored at all (0 weeks) took about 21 days to reach fifty percent sprouting while those stored for fifteen weeks reached fifty percent sprouting in 10 and 13 days for Sauti and Okumkom. respectively. Differences observed among the storage periods were significant at P=0.05 (Table 11). However, differences observed between the varieties were not significant. Table 11. Number of days to fifty percent sprouting in tubers of sweet potato cultivars stored in improved bam and planted in nursery Weeks in storage Cultivar Sauti Okumkom l sd (5./o) 0 21.0 21.7 3.1 5 18.3 17.3 10 9.7 13.3 15 10.0 13.0 LSD(5«/o) N.S. 50 4.I.2.I.3. Effect of storage period on number of days to first vine harvest of sweet potato cultivars planted in nursery In the nursery, the period of storage showed significant differences (P=0.05) in the time to first vine harvest for all storage periods except for 10 and 15 weeks of storage in Sauti (Table 12). In all but 5 weeks o f storage, vines of Sauti were ready for harvesting earlier than those of Okumkom though the differences between the varieties were not statistically significant. Table 12. Number of days to first vine harvest in tubers of sweet potato cultivars stored in improved barn and planted in nursery Weeks in storage Cultivar Sauti Okumkom LSD(S%) 0 78.3 85.7 12.3 5 104.7 102.3 10 63.0 70.0 15 59.7 72.0 LSD(S%) N.S. 51 4.I.2.I.4. Effect of storage period on the number of plants at first vine harvest in sweet potato cultivars planted in nursery At the time o f first vine harvest of each plot, significant differences (P=0.05, and P=0.05 respectively) were observed between the cultivars and the storage period in the number of plants per plot; although no such differences were observed for the interaction. Regarding the storage period, differences observed were between 0 and 5, 10 and 15 weeks o f storage for both cultivars. Differences between 5, 10, and 15 weeks were not statistically significant in Sauti but were so between 15 weeks and 5 and 10 weeks (Table 13). Table 13. Number of plants at first vine harvest in tubers of sweet potato cultivars Weeks in storage Variety Sauti Okumkom l sd (5o/o) 0 99.3 64.3 18.5 5 48.7 58.7 10 47.3 39.7 15 37.0 8.0 LSD(5%) 13.1 4.1.2.1.5, Effect of storage period on the number of plants with vines longer than 30cm at harvest in sweet potato cultivars. Significant differences (P=0.05) were observed between the number o f plants per plot with vines longer than 30cm for both the cultivars and the different storage periods (Table 14) at the time o f first vine harvest. However, differences in the cultivar and storage period interaction were not statistically significant. 52 Table 14. Number of plants with vines longer than 30cm at harvest in sweet potato Weeks in storage Variety Sauti Okumkom LSD(5%) 0 54.7 32. 0 9.1 5 33.0 29.3 10 25.0 23.7 15 23.0 5.3 LSDf5%i 6.4 4.I.2.I.6. Effect of storage period on the initial number of 30cm vines harvested in sweet potato cultivars planted in nursery beds. The initial number o f 30cm vines produced in the first harvest is presented in Figure 4. Significant differences (P=0.05) were observed between the cultivars as well as between the storage periods. Generally, vine production was higher in Sauti than in Okumkom except for Oweeks o f storage in which Okumkom produced more vines than Sauti,. The difference observed here was however not statistically significant. Tubers o f Sauti stored for five weeks gave the highest vine yield at this stage while tubers o f Okumkom stored for 15 weeks gave the lowest number o f 30 cm vines. 4.1.2.1.7 Effect of storage period on the initial mean leaf, mean stem and mean total dry weight of vines harvested in sweet potato cultivars planted in nursery beds. The initial mean leaf, mean stem and mean total (stem dry weight + leaf dry weight) dry weights of the cultivars tested are presented in Table 15. The difference in the mean leaf dry weight between both cultivars was not significant at P=0.05. However, significant differences (P=0.05) were observed among the storage periods. In Sauti, the mean leaf dry weight was lower at 0 weeks o f storage when compared to the mean leaf dry weight of those stored for 5,10 and 15 weeks. The mean leaf dry weight was also lower at 15 weeks of storage than 5 and 10 weeks o f storage. In Okumkom, significant differences 53 were observed only between 10 weeks o f storage and 0, 5, and 15 weeks. In both mean stem dry weight and mean total dry weight, no significant differences were recorded for the period o f storage. However, Sauti produced more mean stem dry weight and mean total dry weight than Okumkom. Table 15. Effect of storage period of tubers on the initial mean leaf, stem and total A Leaf dry weight Weeks in storage Cultivar Sauti Okumkom LSDfs%) 0 2.0 3.3 2.7 5 7.0 3.9 10 6.3 6.8 15 4.3 3.2 LSD(So/o) 1.9 B Stem dry weight Weeks in storage Cultivar Sauti Okumkom LSD(s»/o) 0 3.7 3.4 5.1 5 13.5 4.8 10 12.0 5.5 15 8.4 4.3 LSD(5%) 3.6 C Total dry weight Weeks in storage Cultivar Sauti Okumkom LSD(So/ol 0 5.7 6.7 7.5 5 20.5 8.8 10 18.3 12.3 15 12.7 7.5 LSD(5%) 5.3 54 Fig.4: Effect o f storage period on the total number o f 30cm vines in sweet potato cultivars a t first harvest 250 £ 200 150 100 50 3 Sauti I Okumkom 5 10 Storage time (weeks) 15 55 4.1.2.2 Final vine harvest from tubers planted after a period of storage 4.1.2.2.1 Effect of storage period on number of vine harvests in sweet potato cultivars planted in the nursery. By the beginning o f the rainy season when the experiment ended, the tubers o f both cultivars not stored prior to planting, i.e., 0 weeks o f storage, had been harvested five times, and plots for 5 and 10 weeks o f storage had been harvested three times. With plots where tubers had been stored for 15 weeks before planting, Sauti was harvested 1.7 times and Okumkom was harvested once (Table 16). Differences observed in the number o f times vines were harvested for the storage periods studied were significant (P=0.05). Table 16. Total number of vine harvests in tubers of sweet potato stored in ______________ improved barn and planted in nursery._______________ Weeks in storage Variety Sauti Okumkom LSD(5»/0) 0 5.0 5.0 0.5 5 3.0 3.0 10 3.0 3.0 15 1.7 1.0 LSD(S%', N.S. 4.1.2.2.2 Effect of storage period on vine production of sweet potato cultivars planted in nursery beds. Table 17 shows the number o f apical, middle and basal vines produced by the different treatments. Results indicated significant differences (P=0.05) for both the cultivars and storage periods. There was a marked decrease in the number o f apical vines produced with increased storage period. Figure 5 shows the interaction between the cultivars and storage period. In all cases but 15 weeks o f storage, Sauti produced higher numbers of apical vines than Okumkom. 56 Table 17. Total number of vines harvested per plot in tubers of sweet potato stored in improved barn and planted in nursery. A Total number of apical vines harvested per plot Weeks in storage Cultivar Sauti Okumkom l sd (5%) 0 259.9 55.1 64.6 5 187.3 23.7 10 121.2 27.2 15 46.9 8.7 LSD(S%) 45.6 B Total number of middle vines harvested per plot Weeks in storage Cultivar Sauti Okumkom l sd (5%) 0 129.2 54.0 61.8 5 13.0 8.7 10 3.7 7.0 15 8.0 6.0 l sd (5%) 43.7 C Total number of basal vines harvested per plot Weeks in storage Cultivar Sauti Okumkom l sd <5%> 0 20.2 5.9 N.S. 5 0.0 3.0 10 0.3 2.3 15 0.7 1.7 LSDfS%1 N.S. Generally, the total number o f middle vines harvested per cultivar and storage period decreased with increased storage Significant differences (P=0.05) were observed in both cultivars and in the storage periods. The differences observed between the storage periods were only in relation with Sauti as the LSD values indicated no such differences in the case of Okumkom. The total number o f basal vines harvested for both cultivars for the different storage periods. No significant differences (P=0.05) were observed in both factors studied. 57 4.1.2.2.5 Effect of storage period on the total number of 30cm vines harvested per plot in sweet potato cultivars planted in nursery beds. used to produce vines for field planting. Sauti produced significantly (P=0.05) more 30cm vines than Okumkom for all the different storage periods studied except at 15 weeks. Tubers of both cultivars not stored before vine production yielded the highest 30cm vines followed by those stored for 5, 10 and 15 weeks respectively. Significant differences (P=0.05) were observed between 0 and the storage periods in Sauti. However, no such differences were observed in Okumkom. Figure 6 show the final vine yield of sweet potato tubers stored in the improved bam and Fig.6: Effect of storage period on the total number of 30cm long vines produced in sweet potato cultivars 500 0 □ Sauti H Okumkom o 5 10 15 Storage period (weeks) 58 4.1.2.2.6 Effect of storage period on the percentage vine production in sweet potato cultivars planted in nursery beds. Table 18 shows the percentage vine yield o f sweet potato tubers stored in the improved bam and used to produce vines for field planting. Both cultivars produced more apical Table 18: Effect of tuber storage period on percent vine production in sweet potato cultivars - Final Harvest A Percent apical vine production Weeks in storage Cultivar Sauti Okumkom LSD(s%) 0 69.8 50.4 11.9 5 94.2 66.5 10 97.2 74.0 15 83.7 52.8 LSD(s%) 8.4 B Percent middle vine production Weeks in storage Cultivar Sauti Okumkom LSD(s»/o) 0 26.1 44.4 9.9 5 5.8 24.7 10 2.6 19.5 15 14.8 37.4 LSD(5%) 7.0 C Percent basal vine production Weeks in storage Cultivar Sauti Okumkom LSD(s%) 0 4.1 5.2 N.S. 5 0.0 8.8 10 0.2 6.6 15 1.4 9.7 LSD(5o/o) 2.5 vines than middle vines followed by basal vines. Sauti produced a significantly (P=0.05) higher percentage o f apical vines than Okumkom for all the different storage periods. Okumkom however, produced a higher percentage of middle vines. The percentage basal 59 vines produced did not show any significant differences (P=0.05) between the different storage periods studied in both cultivars. The tubers stored for ten weeks before planting produced the highest percentage apical vines and the lowest percentage o f middle vines. In both cultivars, significant differences (P=0.05) were observed between the storage periods. 4.1.2.2.7 Effect of storage period on dry matter production of vines of sweet potato cultivars planted in nursery. Table 19. Effect of tuber storage period on mean dry weight (g) in sweet potato cultivars- Final Harvest A mean leaf dry weight (g) Weeks in storage Cultivar Sauti Okumkom l sd ,5%> 0 5.1 1.2 N.S. 5 2.0 1.2 10 1.8 0.9 15 3.8 3.2 LSD{So/o) 1.3 B Mean stem dry weight (g) Weeks in storage Cultivar Sauti Okumkom LSD(5%) 0 11.5 3.5 4.5 5 2.6 0.9 10 2.4 0.7 15 7.8 4.3 LSDf5«/ol 3.2 A Mean total dry weight (g) Weeks in storage Cultivar Sauti Okumkom l sd (5%> 0 16.6 4.7 6.2 5 4.6 2.0 10 4.1 1.6 15 11.6 7.5 LSD(5o/o) 4.4 60 Table 19 shows the mean leaf, mean stem and mean total dry weight o f vines o f sweet potato tubers stored in the improved bam and used to produce vines for field planting. Among the cultivars, Sauti produced significantly (P=0.05) higher mean leaf, stem and total dry weight than Okumkom. Storage periods had no significant effect on mean leaf dry weight. However, significant differences (P=0.05) were observed with respect to mean stem and mean total dry weight. 4.2. EXPERIMENT 2: Effect o f spacing o f small unmarketable sweet potato tubers on planting material production o f two sweet potato cultivars. 4.2.1. Effect o f spacing o f small unmarketable tubers on the rate o f sprouting of two sweet potato cultivars. Figures 7, 8 and 9 show sprouting in sweet potato tubers planted at 25 cm x 10 cm, 25cm x 15 cm, and 25 cm x 20 cm. Significant differences (P=0.05) were observed between the two cultivars at the initial stages with Okumkom producing higher number o f sprouts than Sauti. As the experiment progressed, i.e., by 20 days, this difference was no longer significant. However, Okumkom still produced a higher number o f sprouts than Sauti except for the spacing o f 2 cm x 20 cm where Sauti produced more sprouts than Okumkom From 20 days after planting, significant differences (P=0.05) were observed between the planting distances. 61 Fig.7 Rate of Sprouting in Sweet Potato tubers planted at 25cm x 1 Ocm 0 5 12 15 20 26 33 38 47 Number o f Days after planting Fig 8. Rate of Sprouting of Sweet Potato Tubers planted at 25cm x 15cm 0 6 0 - i 0 5 12 15 20 26 33 38 47 Number of Days after planting Fig 9.Rate of Sprouting of Sweet Potato tubers planted at 25cm x 20cm 35 0 5 12 15 20 26 33 38 47 Number of Days after Planting 62 4.2.2. Effect o f spacing o f small unmarketable sweet potato tubers on the rate of increase in the number o f vines longer than 30cm in two sweet potato cultivars. Tables 20 - 23 show the number o f sprouts longer than 30 cm produced after 47, 62, 70 and 77 days after planting. Significant differences (P=0.05) were observed between Okumkom and Sauti 47 and 62 days after planting with Okumkom producing more vines longer than 30cm. No significant differences were observed among the different spacings. Table 20. Effect of spacing of sweet potato tubers on the rate of increase in the Spacing Cultivar Sauti Okumkom LSD(s%) 25 cm x 10 cm 13.3 20.0 N.S. 25 cm x 15 cm 12.3 16.0 25 cm x 20 cm 8.8 12.5 LSD(S%) 3.8 Table 21. Effect of spacing of sweet potato tubers on the rate of increase in the Spacing Cultivar Sauti Okumkom LSD(5o/0) 25 cm x 10 cm 16.3 21.0 N.S. 25 cm x 15 cm 14.5 18.8 25 cm x 20 cm 10.5 14.3 l sd (5W 4.2 Table 22. Effect of spacing of sweet potato tubers on the rate of increase in the Spacing Cultivar Sauti Okumkom LSD,s%) 25 cm x 10 cm 21.3 24.0 N.S 25 cm x 15 cm 17.5 26.5 25 cm x 20 cm 16.0 16.8 LSD(5o/o) N.S. 63 Table 23. Effect of spacing of sweet potato tubers on the rate of increase in the Spacing Cultivar Sauti Okumkom LSD<5%> 25 cm x 10 cm 26.5 27.8 N.S. 25 cm x 15 cm 22.8 32.0 25 cm x 20 cm 20.3 19.3 LSD(s%) N.S. 4.2.3. Effect o f spacing o f small unmarketable sweet potato tubers on vine production in two sweet potato cultivars. Tables 24 to 27 show the effect o f spacing on the number o f plants harvested as well as the number o f apical, middle, basal vines produced by tubers o f two sweet potato cultivars, Sauti and Okumkom. Significant differences (P=0.05) were recorded between the two cultivars for all the parameters. Among the spacings tested, differences were significant (P=0.05) only in the number o f middle vines produced although 25 cm x 20 cm gave the highest number of vines. Figure 10 shows the effect o f spacing on the total number o f 30 cm vines harvested. Table 24. Effect of spacing of tubers on vine production in sweet potato cultivars on Spacing Cultivar Sauti Okumkom LSD(5<>/o) 25 cm x 10 cm 25.8 28.8 N.S. 25 cm x 15 cm 24.5 20.3 25 cm x 20 cm 20.0 16.5 l s d (5o/o) N.S. 64 Fig 10: Effect of spacing on the total number of 30 cm long vines produced in sweet potato cultivars; Sauti and Okumkom 300 i 25x10 25x15 25x20 spacing (cm) Table 25. Effect of spacing of tubers on vine production in sweet potato cultivars on the number of apical vines harvested per plot Spacing Cultivar Sauti Okumkom LSD(5o/o) 25 cm x 10 cm 82.8 12.3 N.S. 25 cm x 15 cm 97.5 11.3 25 cm x 20 cm 77.5 15.5 l sd (5%) 15.9 Table 26. Effect of spacing of tubers on vine production in sweet potato cultivars on the number of middle vines harvested per plot Spacing Cultivar Sauti Okumkom LSD(so/o) 25 cm x 10 cm 26.5 27.8 25.4 25 cm x 15 cm 22.8 32.0 25 cm x 20 cm 20.3 19.3 LSD(so/o) N.S. 65 Table 27. Effect of spacing of tubers on vine production in sweet potato cultivars on the number of basal vines harvested per plot Spacing Cultivar Sauti Okumkom LSD(S%) 25 cm x 10 cm 18.5 8.5 N.S. 25 cm x 15 cm 17.8 11.8 25 cm x 20 cm 16.8 7.0 LSD(s%) 5.2 Table 28. Effect of spacing on the percent (% ) vine production in sweet potato cultivars A Percent (%) apical vine production Spacing Cultivar Sauti Okumkom LSD(5%) 25cm x 10cm 52.3 21.3 9.0 25cm x 15cm 47.4 18.4 25cm x 20cm 53.6 29.9 LSD(5%) 7.4 B Percent (%) middle vine production Spacing Cultivar Sauti Okumkom l s d (5%) 25cm x 10cm 36.0 64.2 8.4 25cm x 15cm 44.5 64.4 25cm x 20cm 35.6 51.5 LSD(5o/o) 6.9 C Percent (%) basal vine production Spacing Cultivar Sauti Okumkom LSD(S%) 25cm x 10cm 11.6 14.5 3.6 25cm x 15cm 8.4 17.2 25cm x 20cm 11.2 18.7 LSD(So/o) 3.0 66 4.2.5. Effect o f spacing o f small unmarketable sweet potato tubers on dry matter production in two sweet potato cultivars. Table 29 shows the mean leaf, mean stem and mean total dry weight o f vines o f sweet potato tubers planted at 25cm x 10cm, 25cm x 15cm and 25 x 20cm. Among the cultivars, Sauti produced significantly (P=0.05) higher mean leaf, stem and total dry weight than Okumkom. However, the mean leaf, mean stem and mean total dry weight for the different spacings were not significant. Table29. Effect of spacing of tubers on mean dry weight of sweet potato cultivars at harvest A mean leaf dry weight Spacing Cultivar Sauti Okumkom L S D (5o/o1 25cm x 10cm 7.3 2.7 N.S. 25cm x 15cm 7.0 3.1 25cm x 20cm 7.3 4.2 l sd (5%) 1.6 B mean stem dry weight Spacing Cultivar Sauti Okumkom l s d (5%) 25cm x 10cm 15.9 4.6 N.S. 25cm x 15cm 18.8 7.8 25cm x 20cm 15.2 8.8 LSD(5%) 3.8 C mean total dry weight Spacing Cultivar Sauti Okumkom LSD(5o/o> 25cm x 10cm 23.1 7.3 N.S. 25cm x 15cm 25.8 10.9 25cm x 20cm 22.5 12.9 l sd (5o/o) 5.1 67 4.3. EXPERIMENT 3: Effect of early initiation of vine multiplication on planting material production of two sweet potato cultivars nurtured in nursery. 4.3.1 Initial Harvest Tables 30 - 34 show initial results o f planting material production from vines o f the two cultivars, Sauti and Okumkom, planted in the field. 4.3.1.1 Effect o f early initiation o f vine multiplication on the number o f plants harvested in two sweet potato cultivars nurtured in nursery. The effect o f early initiation o f vine multiplication in the two cultivars is shown in Table 30. No significant differences (P=0.05) were found among the different times o f initiation of vine multiplication. However, significant differences (P=0.05) were found between the cultivars with Sauti having a higher number o f plants per plot than Okumkom. Table 30. Effect of time of initiation of vine multiplication on the initial number of plants harvested in sweet potato cultivars nurtured in nursery Time of initiation of vine multiplication Variety (weeks before field planting) Sauti Okumkom LSDf5%) 0 17.0 11.0 N.S. 4 19.0 12.7 6 19.3 15.7 8 17.0 14.3 10 18.3 15.0 14 18.0 13.0 LSDo«) 1.4 4.3.I.2. Effect o f early initiation o f vine multiplication on the initial number of 30cm vines harvested in sweet potato cultivars nurtured in nursery Table 31 shows the effect o f early initiation o f vine multiplication on the initial number of 30cm vines produced in the two cultivars. Sauti produced a significantly higher 68 (P=0.05) number o f 30cm vines plants per plot than Okumkom. The differences observed among the different times o f initiation o f vine multiplication were found to be significant at P=0.05. An interaction effect, Figure 11, was also observed among cultivars and the different times o f initiation of vine multiplication. Sauti produced a relatively higher number of 30cm vines with a decrease in the time o f initiation o f vine multiplication whereas Okumkom produced almost the same number o f 30cm vines irrespective o f the time of initiation o f vine multiplication. Table 31. Effect of time of initiation of vine multiplication on the initial number of _______30cm vines harvested in sweet potato cultivars nurtured in nursery_______ Time of initiation of vine multiplication (weeks before field planting) Variety Sauti Okumkom LSD(5%) 0 249.0 88.7 70.3 4 327.0 125.0 6 198.0 153.0 8 228.3 121.3 10 146.3 157.0 14 106.0 81.7 LSDr5o/o) 40.6 4.3.I.3. Effect o f early initiation o f vine multiplication on the initial mean dry matter production in sweet potato cultivars nurtured in nursery Tables 32, 33 and 34 show the effect o f early initiation o f multiplication o f planting material on the initial mean leaf, mean stem and mean total dry weight o f vines o f sweet potato cultivars nurtured in the nursery and used to produce planting material at different times of initiation o f planting material production. Among the cultivars, Sauti produced a significantly (P=0.05) higher mean leaf dry weight than Okumkom (Table 32). The variations between the different times o f initiation of multiplication o f planting material were also highly significant (P=0.05). Sauti at 8 weeks 69 before field planting produced the highest mean leaf dry weight followed by 6 weeks and 4 weeks. 14 weeks and 0 weeks produced about the same mean leaf dry weight and 10 weeks produced the least mean leaf dry weight. On the other hand, Okumkom at 14 weeks before field planting produced the highest mean leaf dry weight followed by 8 weeks and then 6 weeks. 4 and 10 weeks produced about the same mean leaf dry weight and 0 weeks produced the least mean leaf dry weight. Fig. 11: Effect of time of harvest on the total number of 30 cm vines produced in sweet potato cultivars 400 0 300 - CL CO £ 250 > Eo o 200 " 150 o © -Q E 100 50 14 10 8 6 4 0 Time of initiation of vine multiplication (weeks) With regards to the mean stem dry weight (Table 33), Sauti produced a significantly (P=0.05) higher mean stem dry weight than Okumkom. The variations between the 70 different times o f initiation o f multiplication o f planting material were also highly significant (P=0.05). Sauti at 4 weeks before field planting produced the highest mean stem dry weight followed by 8 weeks and 6 weeks. 14 weeks and 0 weeks produced about the same mean stem dry weight and 10 weeks produced the least mean stem dry weight. On the other hand, except for the variation between 0 and 8 weeks recorded, differences between all the treatments in Okumkom were not significant. Table 32. Effect of time of initiation o f vine multiplication on initial mean leaf dry _______________ matter production in sweet potato cultivars __________ Time of initiation of vine multiplication (weeks before field planting) Mean leaf dry weight (g) Sauti Okumkom LSD(o.os) 0 7.8 3.0 3.7 4 11.6 6.1 6 13.6 8.9 8 20.2 8.9 10 4.4 6.1 14 9.8 9.0 LSDfo.o5> 2.1 Table 33. Effect of time of initiation of vine multiplication on initial mean stem dry matter production in sweet potato cultivars, Sauti and Okumkom Time of initiation of vine multiplication (weeks before field planting) Mean stem dry weight (g) Sauti Okumkom LSD(o.os) 0 21.7 6.2 9.3 4 38.2 11.3 6 27.0 12.8 8 35.5 17.0 10 12.1 10.0 14 20.2 8.6 LSDfo.os) 5.3 71 Table 33 represents the mean total dry weight at the first harvest. Among the cultivars, Sauti produced a significantly (P=0.05) higher mean total dry weight than Okumkom. The variations between the different times o f initiation o f multiplication o f planting material were also highly significant (P=0.05). Sauti at 8weeks before field planting produced the highest mean total dry weight followed by 4 weeks and 6 weeks. 14 weeks and 0 weeks produced about the same mean total weight and 10 weeks produced the least mean total dry weight. Similarly, Okumkom at 8 weeks before field planting produced the highest mean leaf, mean stem and mean total dry weight followed by 4 weeks and then 6 weeks. 14 weeks and 10 weeks produced about the same mean total weight and Oweeks produced the least mean total dry weight. Table 34. Effect of time of initiation of vine multiplication on initial mean total dry matter production in sweet potato cultivars Time of initiation of vine multiplication (weeks before field planting) Mean total dry weight (g) Sauti Okumkom LSDfo.osi 0 29.4 9.2 12.5 4 49.8 17.4 6 40.6 21.7 8 56.3 25.9 10 16.5 16.1 14 30.0 17.6 LSD(o.os) 7.2 4.3.2. Final harvest 4.3.2.I. Effect o f early initiation o f vine multiplication on the number of apical vines harvested in sweet potato cultivars nurtured in nursery Early initiation of multiplication o f vines resulted in significantly higher (P=0.05) apical vine yields in Sauti than Okumkom (Table 35). Similarly, significantly higher yield 72 variations (P=0.05) were observed among the various times o f initiating vine multiplication. In Sauti, the differences were observed between Oweeks and 4, 6, 8, 10 and 14 weeks; 4 and 8, 10 and 14 weeks; 6 and 14 weeks and 14 and 8 an 10 weeks. In Okumkom, the differences observed occurred between 0 and 6, 10 and 14 weeks; 4 and 14 weeks; 6 weeks and 14weeks; 8 weeks and 14 weeks and 10 weeks and 14 weeks. Table 35. Effect of time of initiation of vine multiplication on number of apical vines Time of initiation of vine multiplication (weeks before field planting) Number of apical vines Sauti Okumkom LSD(o.os) 0 101.0 20.0 120.3 4 251.6 81.1 6 369.9 179.3 8 400.8 84.2 10 448.1 170.8 14 742.1 371.0 LSD(o.o5) 69.4 4.3.2.2. Effect o f early initiation o f vine multiplication on the number of middle vines harvested in sweet potato cultivars nurtured in nursery Table 36 shows the effect of early initiation o f multiplication o f vines on the number of middle vines produced. Sauti yielded significantly more (P=0.05) middle vines than Okumkom. Significant variations (P=0.05) were observed among the various times of initiating vine multiplication. In Sauti, 0 weeks yielded more middle vines than 4 weeks and less middle vines than 10 and 14 weeks. The number o f middle vines harvested when multiplication was initiated at 4 weeks to field planting was less than the number harvested when vine multiplication was initiated at 8, 10 and 14 weeks. Similarly, initiation o f vine multiplication at 6 weeks yielded a lesser number o f middle vines than 73 when initiation o f vine multiplication began at 10 and 14 weeks before field planting. Similar differences were observed among 8 and 10 and 14weeks initiation of vine multiplication. Similar differences were observed with Okumkom. Table 36. Effect of time of initiation of vine multiplication on number of middle vines produced in sweet potato cultivars Time of initiation of vine multiplication (weeks before field planting) Number of middle vines Sauti Okumkom L SD (o.o5) 0 111.7 54.7 85.2 4 10.3 14.3 6 86.6 170.1 8 155.1 73.7 10 211.0 204.4 14 204.5 248.2 LSDfo.os) 49.2 4.3.2.3. Effect o f early initiation o f vine multiplication on the number of basal vines harvested in sweet potato cultivars nurtured in nursery Early initiation o f multiplication o f vines resulted in significantly higher (P=0.05) basal vine yields in Sauti than Okumkom (Table 37). Similarly, significant variations (P=0.05) were observed among the various times o f initiating vine multiplication. In Sauti, 0 weeks gave the highest basal vine yield followed by 10, 8, 14, 4 and 6 weeks. However, only the differences observed between 4weeks and 0 and 10 weeks; and 6 weeks and 0 and 10 weeks were significant. In Okumkom, the highest number o f basal vines were harvested when multiplication was initiated at 10 weeks to field planting followed by 0, 6, 14, 8 and 4 weeks. Only the differences observed between 10 weeks and 4, 8 and 14 weeks, and 0 and 4 weeks to field planting were significant. 74 Table 37. Effect of time of initiation of vine multiplication on number of basal vines produced in sweet potato cultivars Time of initiation of vine multiplication (weeks before field planting) Number of basal vines Sauti Okumkom LSD(o.o5) 0 37.0 24.7 19.4 4 8.0 3.7 6 6.1 21.0 8 24.2 13.1 10 32.7 39.8 14 19.3 19.9 LSD(o.os) 11.2 4.3.2.4. Effect o f early initiation o f vine multiplication on the final number of 30cm vines harvested in sweet potato cultivars, Sauti and Okumkom nurtured in nursery The effect o f early initiation o f vine multiplication on the final number o f 30cm vines harvested is presented in Figure 12. There were significant differences (P=0.05) among cultivars and time o f initiation o f vine multiplication. Initiating vine multiplication as early as 14 weeks before field planting resulted in the highest vine yield in both cultivars. Differences observed between 0 and 4 weeks were not significant for both cultivars. As initiation of vine multiplication was delayed the resultant vine yield decreased, except for Okumkom at 6 weeks that gave a higher vine yield than Okumkom at 8 weeks. 4.3.2.5. Effect o f early initiation o f vine multiplication on the percentage of the vine parts produced in sweet potato cultivars nurtured in nursery Tables 38, 39 and 40 show the effect o f early initiation o f vine multiplication in Sauti and Okumkom nurtured in the nursery on the percentage vine parts produced. For percentage apical vines produced, Sauti yielded significantly higher (P=0.05) percentage o f apical vines when compared to Okumkom, whereas Okumkom yielded more middle and basal vines than Sauti. 75 Fig. 12: Effect of time of initiation of vine multiplication on the total number of 30cm long vines produced in sweet potato cultivars at final harvest 1200 1400 1000 14 10 8 6 4 0 Time of harvest (weeks) 76 4.3.2.5.I. Effect o f early initiation o f vine multiplication on the percentage of the apical vines produced in sweet potato cultivars nurtured in nursery With respect to the percentage apical vine production (Table 38), significant differences (P=0.05) were observed between all the times o f vine multiplication tested except for 6 and 8 weeks in Sauti and 6, 8 and 10 weeks in Okumkom. The highest percentage of apical vines recorded in Sauti was obtained when multiplication o f vines was initiated at 4 weeks. This was followed by 6, 14, 8, 10 and 0 weeks in a decreasing order. In Okumkom, the highest percentage o f apical vines was obtained at 4 weeks followed by 14, 6, 8, 10 and 0 weeks in a decreasing order. Table 38. Effect of time of initiation of vine multiplication on percentage apical vine production in sweet potato cultivars Time of initiation of vine multiplication (weeks before field planting) Percent apical vines Sauti Okumkom LSD«).o5> 0 42.2 21.1 9.7 4 93.7 78.8 6 80.2 47.2 8 71.2 46.6 10 64.7 43.4 14 76.6 58.4 LSD(o.os) 5.6 4.3.2.5.2. Effect o f early initiation o f vine multiplication on the percentage of the middle vines produced in sweet potato cultivars nurtured in nursery Compared to Sauti, Okumkom produced a higher percentage o f middle vines. Table 39 shows significant differences (P=0.05) in the percentage o f middle vine produced by the cultivars. The variations among the different times o f vine multiplication were also found to be significant (P=0.05). The highest percentage o f middle vines was recorded in 77 Okumkom, when vine multiplication was initiated at 0 weeks followed by 6, 10, 8, 14, and 4 weeks in a decreasing order. Initiation o f vine multiplication at 0 weeks in Sauti also yielded the highest percentage when compared with the other times studied for the same cultivar. Table 39. Effect of time of initiation of vine multiplication on percentage middle vine production in sweet potato cultivars Time of initiation of vine multiplication (weeks before field planting) Percent middle vines Sauti Okumkom LSD(o.o5) 0 43.4 57.0 8.2 4 3.5 15.3 6 18.4 47.0 8 25.4 45.1 10 30.2 47.0 14 21.3 38.3 LSDjo.osi 4.7 4.3.2.5.3. Effect o f early initiation o f vine multiplication on the percentage of the basal vines produced in sweet potato cultivars nurtured in nursery With respect to the percentage basal vine production (Table 40), significant differences (P=0.05) were observed between the cultivars and the times o f vine multiplication. Okumkom had a higher percentage basal vine production than Sauti. For both cultivars initiating vine production at 0 weeks gave the highest percentage o f basal vines. Initiating vine multiplication 8 weeks before field planting in Sauti and 4 weeks before field planting in Okumkom gave the lowest percentage basal yield. 78 Table 40. Effect of time of initiation of vine multiplication on percentage basal vine production in sweet potato cultivars Time of initiation of vine multiplication (weeks before field planting) Percent basal vines Sauti Okumkom LSD(o.os) 0 14.4 22.0 4.2 4 2.9 6.0 6 1.4 5.9 8 3.4 8.3 10 5.0 9.6 14 2.1 3.3 LSD(o.os) 2.4 4.3.3. Effect o f early initiation o f vine multiplication on the final mean dry matter production in sweet potato cultivars nurtured in nursery Tables 41, 42 and 43 show the effect o f early initiation o f multiplication of planting material on the final mean leaf weight, mean stem weight and mean total dry weight o f vines o f sweet potato cultivars raised in the nursery and used to produce planting material at different times o f initiation o f planting material production. 4.3.3.I. Effect o f early initiation o f vine multiplication on the final mean leaf dry weight of vines of sweet potato cultivars nurtured in nursery Sauti produced a significantly (P=0.05) higher mean leaf dry weight than Okumkom as shown in Table 41. The variations between the different times o f initiation of multiplication of planting material were also highly significant (P=0.05) as were the interaction effects of the cultivars and the time o f initiation o f vine multiplication. Sauti at 0 weeks before field planting produced the highest mean leaf dry weight followed by 10 weeks, 6 and 8 weeks. 14 and 4 weeks produced about the least mean leaf Similarly, Okumkom at 0 weeks before field planting produced the highest mean leaf dry weight 79 followed by 6 weeks and then 10 weeks. 8 weeks and 10 weeks produced about the same mean leaf dry weight and 4 weeks produced the least mean leaf dry weight. The interaction effect between the cultivars and time o f initiation o f vine multiplication was significant only at 0 weeks when Sauti yielded a significantly higher mean leaf dry weight than Okumkom. Table 41. Effect of time of initiation of vine multiplication on final mean leaf dry _______________ matter production in sweet potato cultivars __________ Time of initiation o f vine multiplication (weeks before field planting) Mean leaf dry weight (g) Sauti Okumkom LSD(o.os) 0 7.8 3.0 1.3 4 1.2 0.8 6 3.1 3.0 8 2.4 1.0 10 3.4 1.4 14 1.2 1.0 LSD(o.os) 0.7 4.3.3.2. Effect o f early initiation o f vine multiplication on the final mean stem dry weight of vines of sweet potato cultivars nurtured in nursery Regarding final mean stem dry weight as shown in Table 42, Sauti produced a significantly (P=0.05) higher mean stem dry weight than Okumkom The variations between the different times o f initiation o f multiplication o f planting material were also highly significant (P=0.05) as were the interaction effects o f the cultivars and the time o f initiation o f vine multiplication. Sauti at 0 weeks before field planting produced the highest mean stem dry weight followed by 10 weeks, 8, 6 and 14 weeks and 4 weeks. As in the case o f Sauti, Okumkom at 0 weeks yielded the highest mean stem dry weight and this varied significantly from the other times studied. Delaying initiation o f vine 80 multiplication resulted in Sauti producing a higher stem dry weight when compared to Okumkom. Table 42.Eeffect of time of initiation of vine multiplication on final mean stem dry _______________ matter production in sweet potato cultivars __________ Ti me of initiation of vine multiplication (weeks before field planting) Mean stem dry weight (g) Sauti Okumkom LSD(o.os) 0 21.6 6.2 2.9 4 2.1 0.9 6 4.3 2.8 8 4.9 1.3 10 7.0 2.2 14 2.7 0.9 LSD(o.os) 1.7 4.3.3.3. Effect o f early initiation o f vine multiplication on the final mean total dry weight of vines of sweet potato cultivars nurtured in nurseiy Table 43 represents the mean total dry weight at final harvest. Among the cultivars, Sauti produced a significantly (P=0.05) higher mean total dry weight than Okumkom. The variations between the different times o f initiation o f multiplication o f planting material were also highly significant (P=0.05). An interaction effect was also observed at 0 weeks of initiation o f vine multiplication as shown in the figure. Sauti at 0 weeks before field planting produced the highest mean total dry weight followed by 10, 6 and 8 weeks. 14 and 4 weeks produced the least mean total weight. Similarly, Okumkom at 0 weeks before field planting produced the highest mean total dry weight and 4 weeks produced the least. The interaction effect showed that delaying initiation o f vine multiplication resulted in Sauti producing a higher mean total dry weight when compared to Okumkom). 81 Table 43. Effect of time of initiation of vine multiplication on final mean total dry matter production in sweet potato cultivars Time of initiation of vine multiplication (weeks before field planting) Sauti Okumkom LSD(o.os) 0 29.4 9.2 4.0 4 3.3 1.7 6 7.4 5.8 8 7.3 2.4 10 10.4 2.5 14 3.9 1.9 LSD(o.os) 2.3 82 CHAPTER FIVE 5.0 DISCUSSION 5.1 Storage of small unmarketable sweet potato tubers. The bam used in the study consisted o f a wooden frame and 5mm mesh expanded metal. It was constructed as such so as to offer the maximum ventilation possible. It was roofed with thatch extending sufficiently over the sides to exclude direct sunshine from shelf area, Plates 1 and 2. Temperature and relative humidity values recorded during the period of study were 28.9 - 29.8°C and 68.5 - 79.8%RH (taken at 1:00pm). The tubers did not store well in this bam although these conditions fit the description o f rural storage structures, made by Bani and Josiah, (1995). Sixty percent o f Sauti and 26% of Okumkom were lost by the end o f the fifth week o f storage. This increased to 66% and 69% for Sauti and Okumkom respectively by the tenth week; and by the end o f the experiment fifteen weeks after storage, 72% o f Sauti and 89.3% o f Okumkom were lost (Table 9, Figure 2). The optimum conditions for sweet potato storage have been reported by Data et al. (1989) and Onwueme and Sinha (1991), as 15°C and 85-90% RH. Under these conditions certain cultivars like the Jewel have been stored for up to nine months (Wilson et al., 1992). However, they all agreed that the attainment o f such conditions was not economically feasible for most parts o f the tropics. For storage o f produce under tropical conditions, Kamalam, et al., (1998), recommended the use o f bam, pit, clamp storage, and storage in wooden boxes, baskets, sawdust, and sand. Other studies also indicated 83 that sweet potatoes can be stored for between one and four months under these conditions (MOA, 1988; Data et al., 1989; Kamalam, et al., 1998; Satish et al., 1999; Sowley, 1999). The high percentage losses recorded in the present study can be attributed to the high temperature and low relative humidity that led to high respiratory activity. Another reason may be due to the fact that the tubers were too small, and so were adversely affected by factors such as weight loss, shriveling, rotting, and insect damage. The high percentage tuber losses obtained during storage in the dry season from October to January, and the resultant low 30cm vine yields obtained from tubers planted at the end of the experiment (in April at the beginning o f the rainy season) is an indication that storing tubers in the bam for a period before planting them in the field to produce vines for field planting may not be advisable since a high proportion o f the tubers could be lost during storage. 5.1.1. Weight loss and shriveling in stored sweet potato tubers. The weight o f the tubers studied ranged from 20g to 200g, with majority o f them weighing between 80g to 120g. The percentage weight loss and shriveling increased significantly with increase in period o f storage. By the end o f fifteen weeks, weight loss in Sauti was 27.7% and 40.4% in Okumkom. Similarly 84% of Sauti and 88.9% of Okumkom tubers were shriveled (Tables 5 & 6). During the study, it was observed that more o f the smaller sized tubers shriveled than the larger sized ones. As small objects have wider surface areas, and the rate o f transpiration increases with increased surface 84 area, the small sizes o f the tubers could have resulted in an increase in the rate of transpiration and contributed to the high percent shriveling. Further studies would be necessary to determine the most reasonable sizes o f tubers that could be stored for later generation o f planting material without compromising on marketability. Nair (2000), recommended the use o f tubers o f 125 to 150g weight for vine production. Storage o f fresh tubers in moist sawdust, sand, and under ambient conditions have been studied, and results have shown weight losses o f 11.4%, 9.88% and 40.71% respectively after 6 weeks o f storage (Data et al., 1989). Sowley (1999) reported fresh weight losses o f up to 22.69% in sweet potatoes stored for 8 weeks in storage bam. Satish et al. (1999) observed shrinkage in tubers after 7 to 12 weeks o f storage. Although Data et al., (1989) had reported that weight loss and shriveling could adversely affect table quality no such effect had been reported in the case o f tubers being stored for planting material production at a later date. Some of the tubers under this study were however not suitable for planting because they were completely shriveled. 5.1.2. Rotting in stored sweet potato tubers. In this study, the percentage tuber rot increased with storage period. In Sauti rotting increased from 26.7% in the 5th week to 34.8 by the 15th week (Table 7 & Plates 3, 4, 5 & 6), whereas in Okumkom, it increased from 22.2% in the 5th week to 58.3% in the 15th week. This indicates that rotting is a serious problem in sweet potato storage. Kamalam et al. (1998) reported that in storage, sweet potatoes are subjected to several types o f post 85 harvest losses including pathological decay, and losses due to diseases particularly soft rots could be very substantial. Sowley (1999) also observed a general increase in the severity o f rot in tubers stored and concluded that the maximum storage period for sweet potatoes is one month. This study shows that to avoid a total loss o f material, it may be advisable not to store tubers beyond 5 weeks, especially for Okumkom. On the other hand other forms o f pre storage treatments like hormone treatment, fungicide application and irradiation could be studied and if possible recommended for the extension o f storage life. It is possible to control tuber rots in storage by the application o f irradiation. [Avakyan et al., (1974); Adesiyan; (1977); Maghrabi and El-Sayed (1988); Gasiorowska and Zarzecka (2000) and USEPA (2002)]. Botryodiplodia theobromae was identified as the pathogen that caused the rot in the tubers stored in the present study, a confirmation o f observations by Edmond (1971b) and Sowley (1999). 5.1.3. Dormancy and sprouting in stored sweet potato tubers. The results o f Experiment 1 showed that, sprouting had occurred in both cultivars by the 5th week o f storage and increased with further increases in period o f storage. In Sauti 13.5% o f the tubers had sprouted by the 5th week and increased to 62.8% by the 15th week. In Okumkom 20% of tubers had sprouted by the 5th week. This increased to 60.6% in the 15th week (Table 8; Plates 7a, 7b, 8 and 9). Once steps are taken to control shriveling, rotting and insect damage, storing tubers could provide a convenient means of 86 conserving planting material so long as sprouted tubers are kept under such conditions that prevent deterioration. At the end o f his study, Sowley (1999) proposed that sweet potato tubers stored could be used to generate planting material when necessary. Tubers not stored at all before field planting yielded the most vines. The possibility o f irradiating tubers, and/or the use of sprout inhibiting chemicals like isopropyl-N- chlorophynylcarbamate to delay sprouting and thus extend storage life could be explored so that nursery activities could be initiated by the fifteenth to twentieth week after storage. If this is done nursery activities could be further delayed and labour could be employed elsewhere (Avakyan et al., 1974; Adesiyan, 1997; Diop, 1998; USEPA, 2002). Sweet potato is said to have no state o f dormancy, that is, it can sprout in spite o f an unfavourable environment (Sowley, 1999). Satish et al. (1999) observed sprouting between 3 to 8 weeks o f storage. Sowley (1999) reported that the rate o f sprouting increased with increase in the period o f storage and observed that up to 40% of the tubers stored sprouted within the first week and up to 98.1% o f tubers had sprouted by the eighth week o f storage. Although his results were higher than those obtained in this study the trend in sprouting was similar as sprouting in tubers o f Sauti increased from 13.5% in the fifth week to 62.8% in the fifteenth week. Sprouting in tubers o f Okumkom increased from 20% in the fifth week to 60.6% in the fifteenth week. 87 With respect to insect damage, significant differences were observed between the varieties with Suati being more susceptible to insect damage than Okumkom in storage. The main pest was identified to be the sweet potato weevil (Cylas puncticollis). The percent infestation in Sauti (42.8%) and Okumkom (12.2%) 15 weeks after storage were quite high, and is similar to that reported by Otoo (1998). Cylas infestation normally occurs in the field prior to storage (Theberge 1985; Missah and Kissiedu, 1994; Capinera, 1998). It is therefore possible that the tubers studied had been infected in the field prior to storage because the bam had been rehabilitated and disinfected before tubers were introduced and so could not have been the source o f infestation. The differences could also have resulted from the sorting o f the tubers prior to storage. Sowley (1999) demonstrated that the sweet potato weevil, Cylas sp. was the most important pest associated with sweet potato storage in Ghana. Indeed attack by sweet potato weevil is a major constraint associated with sweet potato production (Theberge 1985; Missah and Kissiedue? al 1994; Capinera, 1998; and Sowley, 1999). Practising farm hygiene, removal o f alternate hosts, early harvesting and stringently sorting before storage could prevent infestation in storage (Onwueme and Sinha, 1991; Missah & Kissiedu, 1994; Diop, 1998). Irradiating tubers prior to storage could also destroy eggs and larvae already laid inside tubers and prevent tuber damage during storage (Avakyan et al., 1974; Adesiyan, 1997; USEPA, 2002). 5.1.4. Insect damage in stored sweet potato tubers. Generally, no significant variations were observed among the cultivars tested in relation to percentage weight loss, shrinkage, percentage sprouting and percentage rotting in storage. This implies that the cultivars were similarly affected by the storage conditions. These results are in disagreement with those of Data et al (1989), and Wilson et al. (1992) who reported that different sweet potato varieties behaved differently even under optimum conditions with some storing for longer periods than others. 5.2. Conservation of sweet potato tubers and vines in the nursery. Results obtained from the experiments all show that planting material o f Sauti and Okumkom can be obtained at the time o f field planting if small unmarketable tubers or vines are raised in the nursery during the dry season. The higher number o f 30cm vines and dry matter contents obtained for Sauti when compared to Okumkom confirm the fact that some sweet potato cultivars are more tolerant to drought than others (Hahn, 1977). For almost all the experiments in this study, Sauti produced a significantly higher number of 30cm vines and a higher percentage o f apical vines than Okumkom, suggesting that Sauti branched more and was more tolerant to drought. Between January and March, when the temperatures increased slightly (Appendix lb&c), some vine multiplication was done on both varieties. It was observed that vines o f Sauti had better establishment and were more vigorous than those of Okumkom. The cumulative effects o f these reflected 5.1.5. Behaviour of tubers of sweet potato cultivars in storage. 89 in the final vine yields obtained. These findings agree with Otoo et al., (1998) who indicated that apart from the higher mean tuber yields obtained by Okumkom in almost all the agroecologies in the country, Sauti had a better plant establishment, fresh vine production and a higher biomass production than Okumkom On the whole, vine yields obtained for both cultivars were low when compared to the number of vines required per hectare. For Experiment 1, the highest yields o f 409 vines obtained from an initial number o f 50 unmarketable tubers planted at 10cm intervals on an area o f 0.5m2 implies that 4,900 o f these tubers would have to be planted on an initial area of 49m2 to be able to produce an equivalent o f 40,000 vines necessary to establish one hectare o f sweet potato. This number o f unmarketable tubers could still represent quite a volume and using these to generate planting material may not look attractive to a prospective farmer. A probable alternative could be to further explore the use of tissue culture techniques on a commercial basis to conserve planting material during the dry season, and multiplying them to provide adequate number o f vines at the onset o f the rains. This technique is already being employed successfully in other countries including China (Fuglie et. al., (1999) For Experiment 3, planting vines at 40cm x 40cm on a plot o f 3m x 0.6m and initiating multiplication o f planting material 14 weeks before field planting yielded the highest number of 966 vines. By extrapolation, initially planting vines at 40cm x 40cm on a plot of 33.2m2, and initiating vine multiplication 14 weeks before field planting would yield 90 about 40,000 vines, enough to plant one hectare. When compared to delaying harvesting to 10, 8, 6 or 4 weeks before field planting, this yield may be significant. However, the total number o f 7 harvests made for the treatment in which vine multiplication was initiated at 14 weeks before field planting as against 3 harvests for the others raises the question of labour and other input costs. Although this study did not consider the cost of production, it may seem more suitable to increase the initial area planted, raise the vines for the early part o f the dry season and initiate vine multiplication 10 to 8 weeks before field planting in order to reduce the number o f harvests and save on labour. Further studies could be done to determine the possibility o f reducing the initial number of unmarketable tubers stored and increasing the number o f sprouts per tuber, in order to further increase the planting material yields. The effect o f fertilizer application and/or organic manuring and possibly the effect o f shading o f sweet potato vines in the dry season could also be evaluated as Ravi (2000) indicated that shading has some effect on vine production and tuber yields in sweet potato. The results obtained from these studies are relevant because, they suggest an alternate way of conserving and multiplying planting material for the rainy season. This is because whereas some crop yield may be obtained under harsh growing conditions, conservation of planting material over a long dry season is necessary if material is to be available for planting at the onset o f the rains (Onwueme and Sinha, 1991; Otoo, 1998; Kakraba, 2000). Sweet potato vines do not store for more than seven days hence, specific 91 arrangements to provide material for the crop that is harvested at a time when a new crop is not being planted must be made, and techniques for producing large quantities o f the planting material must be developed (Okoli, 1988). It has been proposed that where the non-growing season is either too long or too severe for vines to survive, apart from maintaining a small, well-watered plot o f sweet potatoes, tubers could be stored for some time( Onwueme and Sinha, 1991; and Yankey, 2001). A few weeks before the start o f the growing season, they could be buried in moist soil, and sprouts from the tubers harvested at intervals and planted on the field. Rapid establishment and superior maintenance o f top growth under extreme stress are vital characteristics to ensure availability o f planting materials during the short rainy periods that occur in the dry lands o f Africa (CIP, 1995). Sprouting in the two cultivars under the different planting distances showed significant variations at the initial stages with Okumkom having more sprouts than Sauti, but the variations were no longer significant by the twentieth day after planting. Beyond this period, results showed no significant variations among the cultivars and planting distances tested, although both cultivars planted at 25cm x 10cm produced the highest number of sprouts and gave the highest 30cm vine yields as well as apical, middle and basal vines produced. Carey et al. (1997) reported that in a study undertaken to examine differences in sprouting ability among CIP-bred clones significant variations were 92 observed in the sprouting ability o f the different cultivars. In addition, clones found to produce the highest number o f sprouts sprouted earliest. Missah and Kissiedu, (1994) observed that the weight o f vines decreased with time probably due to age and drying environmental conditions. Although the variations between the different times o f initiation o f vine multiplication which correspond to the age o f vines in nursery beds was highly significant, it did not follow the same trend. The highest total dry weight for both cultivars was obtained at 8 weeks before field planting whereas 10 weeks and 0 weeks before field planting yielded the lowest dry matter. Having spent 5 months in the field, dry matter yields o f vines obtained at 0 weeks would have been expected to be low, since a major portion o f the vine dry mater would have been partitioned to the roots for tuber formation (Ravi, 2000). 5.3. Vine yield resulting from early initiation of vine multiplication. Further to conservation o f tubers and vines during the dry season, this study explored the possibility of initiating vine multiplication early in order to obtain a higher number of vines for field planting. Results obtained from Experiment 3 showed that early initiation of vine multiplication increased number o f vines available for field planting. Initiation of vine multiplication at 14 weeks before field planting gave the highest vine yield. As the time of initiation o f vine multiplication was delayed, the number o f vines obtained decreased consistently until the time when no multiplication was done. This could be due to the fact that whereas the vines harvested 14 weeks before field planting had the 93 opportunity to rejuvenate after being cut and replanted, partitioning o f photosynthate from source to sink, and senescence o f the older vines could have begun for those treatments in which vine multiplication was further delayed resulting in the lower planting material yields observed. Rapid establishment and superior maintenance o f top growth under extreme stress are vital characteristics to ensure availability o f planting materials during the short rainy periods that occur in the dry lands o f Africa (CIP, 1995). For almost all the experiments in this study, Sauti produced a significantly higher number o f 30 cm vines than Okumkom, suggesting that Sauti was more tolerant to drought. These findings agree with Otoo et al., (1998) who indicated that apart from the higher mean tuber yield obtained by Okumkom in almost all the agroecologies in Ghana, Sauti had a better plant establishment, fresh vine production and a higher biomass production than Okumkom. 5.3.1. Vine parts For vines conserved in the field the highest apical, middle, basal and hence total vine yields for both cultivars were obtained when multiplication was initiated fourteen weeks before field planting. The percentage apical vines were highest for all the treatments studied. There was a consistent decrease in the respective numbers o f 30 cm vines harvested in the subsequent treatments except for harvests made six weeks before field planting This implies that instead of simply maintaining vines in a nursery during the dry season, the number o f planting material available for field planting could be increased 94 further by early initiation o f multiplication. Furthermore, a higher number o f apical vines could be obtained with this practice and as reported by other workers (Du Plooy et al., 1988; Nair et al., 1989; Onwueme and Sinha, 1991; Hossain and Mondal, 1994; and Hoa, 1998), the higher number o f apical vines when planted would result in higher yields than when stem vines were planted thus, tuber yields could be increased if multiplication of planting materials is initiated early. 95 CHAPTER SIX 6.0. CONCLUSIONS Judging from the number o f tubers remaining after each set period o f storage, it appears that there is no advantage in storing small unmarketable sweet potato tubers after harvest during the early part o f the dry season, i.e., from October to January, to be used later in the season from November to January for planting material production unless adequate measures are taken to prevent or control Cylas infestation, rotting and excessive shriveling. Although weight loss per se may not result in tuber damage, excessive shriveling, rotting and insect damage could result in tubers losing viability and becoming unacceptable for planting after five, ten and fifteen weeks o f storage. With respect to planting material production from tubers, the vine yield obtained after multiplication in the field suggests that planting the tubers at 25cm x 15cm immediately after curing and watering them regularly to ensure that they do not dry out under the harsh conditions of the dry season could give the most vines for field planting. Results obtained from Experiments 1, 2 and 3 all show that planting material o f Sauti and Okumkom can be obtained at the time o f field planting if small unmarketable tubers or vines are raised in the nursery during the dry season. However, to obtain a higher number of vines and especially a higher number o f apical vines which when planted would result in higher yields, vine multiplication could be initiated as early as fourteen weeks before field planting. 96 4,900 (four thousand, nine hundred) o f these tubers would be required to produce an equivalent o f 40,000 vines necessary to establish one hectare o f sweet potato on an initial area o f 49 m2. On the other hand, planting vines at 40 cm x 40 cm on a plot o f 33.2 m2, and initiating vine multiplication 14 weeks before field planting would yield about 40,000 vines, enough to plant one hectare. The following recommendations are being made based on this study 1. To conserve sweet potato planting material during the dry season, small unmarketable tubers could be planted at 0.25m x 0.15m immediately after curing and watered regularly to ensure that they do not dry out under the harsh conditions o f the dry season. 2. To increase the number of planting materials, especially the number o f apical vines available for field planting, multiplication o f vines should be initiated between fourteen and six weeks before planting. 3. For further improvement, studies should be done to determine the most suitable tuber weights to be stored for planting material production. The possibility of reducing the initial number o f unmarketable tubers to be stored, the effect of irradiation, the application of sprout inhibiting chemicals like CIPC (isopropyl-N- chlorophenylcarbamate) and fungicides on the extension of storage life o f the 97 tubers and the use o f tissue culture to conserve and multiply planting materials could also be studied. 4. In the field, the effect o f fertilizer application and/or organic manuring and possibly the effect o f shading o f sweet potato vines in the dry season could be investigated. 98 REFERENCES Adesiyan, S. O. (1977). 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MEAN TOTAL RAINFALL FIGURES (MM) AND RAIN DA VS (IN BRACKETS) FOR 1997-2002 YEAR September October November December January February March April 1996-97 27.9(7) 9.9(2) 7.2(2) 22.1(2) 1.8(1) 0(0) 138.9(11) 76.4(9) 1997-98 72.9(1) 83.3(10) 41(3) 74.6(4) 0(0) 42.9(1) 6.9(1) 24.5(2) 1998-99 23.5(6) 130(7) 6.9(3) 9.1(3) 39.4(3) 46.4(4) 17.2(2) 50.8(5) 1999-00 25.7(8) 69.3(8) 6.9(4) 12.7(4) 11.7(2) 0(0) 60.2(3) 21.4(4) 2000-01 5.5(3) 50.2(2) 28.2(2) 25.2(4) 0(0) 0.5(1) 57.1(8) 141(6) 2001-02 54.3(8) 43.3(4) 14.1(4) 9.7(3) 125.2(1) 29.8(3) 45(4) 136.8(7) Source: Ghana Meteorological Services. APPENDIX lb. MEAN MONTHLY MAXIMUM TEMPERATURE (°C) FOR 1997-2002 YEAR September October November December January February March April 1996-97 28.9 31.4 32.8 32 32.7 34.3 32.3 31.5 1997-98 31.1 31.6 32.4 32.1 33.5 34.6 35 35.1 1998-99 30.7 31.4 32.9 33.3 32.6 33.7 33.9 33.4 1999-00 29.1 30.8 32.5 32.9 32.9 34.5 34.1 33.2 2000-01 30.4 32.3 32.7 32.8 33 34.3 38.2 32.7 2001-02 28.9 31.4 32.1 32.8 32.2 33.7 33.1 32.9 Source: Ghana Meteorological Services. 120 APPENDIX lc. MEAN MONTHLY MINIMUM TEMPERATURE (°C) FOR 1997-2002 YEAR September October November December January February March April 1996-97 22.7 23.2 24 24 24.3 24.4 24.2 24.1 1997-98 23.5 23.8 24.1 23.9 22.1 25.4 26.3 25.4 1998-99 23.3 23.8 24.6 24.3 24.3 23.9 24.5 24.4 1999-00 22.8 23.3 23.9 24.3 24 23.8 25.4 24.8 2000-01 22.9 23.5 24.2 24.1 23.8 23.8 24.1 24.2 2001-02 22.3 23.4 24.1 24.7 23.1 24.1 24.5 24.4 Source: Ghana Meteorological Services. APPENDIX .Id. MEAN MONTHLY RELATIVE HUMIDITY (%) AT 6:00 HOURS FOR 1997-2002 YEAR September October November December January February March April 1996-97 94 92 94 94 93 88 92 92 1997-98 92 94 94 92 88 92 91 90 1998-99 92 94 94 93 93 91 92 90 1999-00 95 93 94 93 91 87 91 90 2000-01 92 92 93 92 91 87 90 90 2001-02 93 93 93 95 90 88 91 91 Source: Ghana Meteorological Services. 121 APPENDIX le. MEAN MONTHLY RELATIVE HUMIDITY (%) AT 15:00 HOURS FOR 1997-2002 YEAR September October November December January February March April 1996-97 74 68 66 68 66 58 66 70 1997-98 69 68 68 70 54 62 64 63 1998-99 68 70 73 64 67 62 64 62 1999-00 73 71 67 60 62 48 59 61 2000-01 69 66 68 65 63 55 63 64 2001-02 74 70 67 67 59 61 64 67 Source: Ghana Meteorological Services. APPENDIX 2: EXPERIMENT 1 (BARN STORAGE) EFFECTS OF STORAGE PERIOD ON TUBERS ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES Tuber Loss Tuber Wt Loss Tuber Cuts Tuber Breakages Tuber Sprouts Tuber Rots Tubers Shrivel Insect Damage Variety (A) 1 0.0003 156.1 312.48** 7.48 326.3 186.5 82.1 380.81** Storage (B) 3 1.0384** 126.8** 26.42 44.44 4757.4** 2375.1** 7930.9** 945.76** A x B 3 0.1201** 78.8 36.43 71.43 231 238.9 447.7 342.05** Error 16 0.0064 359.9 29.59 80.14 366.3 179.7 250.5 43.55 ** Significant at both 1% and 5% levels of probability 122 APPENDIX 3: EXPERIMENT I (FIELD) EFFECTS OF PERIOD OF TUBER STORAGE ON VINE PRODUCTION - FIRST HARVEST ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES # Of days to 50% sprouting %Of tubers stored # Of tubers planted # Of days to first harvest Total # of 30cm vines # Of vines longer than 30cm + 2 nodes Number of plants at harvest Variety (A) 1 15.042 60.167 15.042 222.042 4873.500** 770.67** 1426.042* Storage (B) 3 142.931** 7559.278** 1889.819** 1876.042** 10564.111** 899.39** 3649.486** A x B 3 6.931 691.278** 172.819** 56.153 3142.278** 163.67 637.042 Error 16 6.583 48.500 12.125 101.458 540.417 56.99 227.625 * Significant at 5% level of probability ** Significant at both 1% and 5% levels of probability APPENDIX 4: EXPERIMENT 1 (FIELD) EFFECTS OF PERIOD OF TUBER STORAGE ON DRY MATTER PRODUCTION - FIRST HARVEST ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES Leaf dry weight Shoot dry weight Total dry matter Variety (A) 1 2.137 143.298* 180.431* Storage (B) 3 18.062* 40.039 108.277 A x B 3 5.619 19.371 41.131 Error 16 4.821 17.653 37.304 * Significant at 5% level of probability 123 APPENDIX 5: EXPERIMENT 1 (FIELD) EFFECTS OF PERIOD OF TUBER STORAGE ON VINE PRODUCTION - FINAL HARVEST ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES # Of harvests # Of 30cm apical vines # Of 30cm middle vines # Of 30cm basal vines Total ft of 30cm vines Variety (A) 1 0.167 93987.650** 2296.148* 25.73 129286.760** Storage (B) 3 13.500** 17825.851** 10581.750* 205.739 57476.734** A x B 3 0.167 8179.461* 2080.480 100.430 18527.126 Error 16 0.167 2782.163 2545.780 64.805 11774.015 * Significant at 5% level of probability ** Significant at both 1% and 5% levels of probability APPENDIX 6: EXPERIMENT 1 (FIELD) EFFECTS OF PERIOD OF TUBER STORAGE ON VINE PRODUCTION - FINAL HARVEST ANALYSIS OF VARIANCE TABLE Sources of MEAN SQUARES Variation Df % Apical vines % Middle vines % Basal vines Variety (A) 1 3845.916** 2202.276** 227.619** Storage (B) 3 799.131** 718.059** 4.970 A x B 3 38.066 8.894 18.693 Error 16 94.793 65.834 8.583 Significant at 5% evel of probability ** Significant at both 1% and 5% levels of probability 124 APPENDIX 7: EXPERIMENT 1 (FIELD) EFFECTS OF PERIOD OF TUBER STORAGE ON DRY MATTER PRODUCTION - FINAL HARVEST ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES Leaf dry weight Shoot dry weight Total dry matter Variety (A) 1 14.815* 82.981* 167.919** Storage (B) 3 7.172 54.663* 99.422* A x B 3 3.741 13.502 30.574 Error 16 2.305 13.304 26.030 * Significant at 5% level of probability APPENDIX 8: EXPERIMENT 2 (FIELD) EFFECT OF SPACING ON THE NUMBER OF SPROUTS PRODUCED ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES # Of tubers planted 5 DAP 12 DAP 15 DAP 20 DAP 26 DAP 33 DAP 38 DAP 47 DAP Variety (A) 1 1.500 0.375 1148.167* 1040.167* 513.375 322.667 228.167 216.000 192.667 Spacing (B) 2 451.500** 0.125 497.792 642.792 827.542* 1229.292* 1012.875* 1287.875* 1250.042* A x B 2 1.500 0.125 280.292 206.792 99.125 113.042 82.542 90.125 72.042 Error 18 1.500 0.208 177.528 230.778 214.625 230.917 200.500 250.472 248.917 * Significant at 5% level of probability ** Significant at both 1% and 5% levels of probability 125 APPENDIX 9: EXPERIMENT 2 (FIELD) EFFECT OF SPACING ON THE NUMBER OF SPROUTS LONGER THAN 30CM ANALYSIS OF VARIANCE MEAN SQUARES Sources of Variation Df 47DAP 62DAP 70DAP 77DAP Variety (A) 1 135.375* 108.375 104.167 60.167 Spacing (B) 2 72.667* 81.500 94.792 150.125 A x B 2 6.000 0.500 37.042 58.042 Error 18 19.958 23.681 37.750 56.556 * Significant at 5% leve o f probability APPENDIX 10: EXPERIMENT 2 (FIELD) EFFECT OF SPACING ON THE NUMBER OF VINES PRODUCED ANALYSIS OF VARIANCE Sources of Variation Df MEAN SQUARES Total plant harvest Total vines produced Apical 30cm vines Middle 30cm vines Basal 30cm vines Variety (A) 1 15.042 79120.167** 31901.042** 6834.375** 442.042** Spacing (B) 2 162.375 3969.042 147.042 2222.167* 16.625 A x B 2 31.792 998.292 302.792 435.500 10.042 Error 18 82.347 2015.278 342.069 582.736 37.014 * Significant at 5% level of probability ** Significant at both 1% and 5% levels of probability 126 APPENDIX 11: EXPERIMENT 2 (FIELD) EFFECT OF SPACING ON THE % APICAL, MIDDLE, AND BASAL VINE PRPDUCTION ANALYSIS OF VARIANCE TABLE Sources of MEAN SQUARES Variation Df % Apical vines % Middle vines %Basal vines Variety (A) 1 4671.716** 2716.392** 245.818** Spacing (B) 2 157.036 242.174* 10.920 A xB 2 27.798 78.203 19.328 Error 18 73.971 64.170 12.009 ** Significant at both 1% anc 5% levels of probability APPENDIX 12: EXPERIMENT 2 (FIELD) EFFECT OF SPACING ON THE DRY MATTER PRPDUCTION ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES Mean leaf dry weight Mean stem dry weight Mean total dry weight Variety (A) 1 90.04** 546.501** 1080.203** Spacing (B) 2 1.320 18.899 22.211 A x B 2 0.962 15.046 22.949 Error 18 3.564 19.682 35.181 ** Significant at both 1% anc 5% levels of probability 127 APPENDIX 13: EXPERIMENT 3 - INITIAL HARVEST EFFECT OF TIME OF INITIATION OF MULTIPLICATION OF PLANTING MATERIAL ON VINE PRODUCTION ANALYSIS OF VARIANCE TABLE Sources of Variation Df MEAN SQUARES Number of plants harvested Total harvest Number of 30 cm vines Mean leaf dry weight Stem dry weight Total dry weight Variety A) 1 182.250** 182.25** 69696.00** 168.39** 1974.143** 3295.602** Storage B) 5 8.361 8.361 11022.044* 79.69** 232.685** 529.642** A x B 5 3.383 3.383 10268.00* 32.48** 99.803 209.724 Error 24 4.306 4.306 3483.139 9.606 60.619 110.462 * Significant at 5% level of probability ** Significant at both 1% and 5% levels of probability APPENDIX 14: EXPERIMENT 3 - FINAL HARVEST EFFECT OF TIME OF INITIATION OF MULTIPLICATION OF PLANTING MATERIAL ON VINE PRODUCTION ANALYSIS OF VARIANCE Sources of Variation Df MEAN SQUARES Total vines produced Apical 30 cm vines Middle 30 cm vines Basal 30 cm vines Variety (A) 1 508351.095** 494954.559** 48.215* 6.318* Harvest (B) 5 338148.061** 166869.063** 42319** 746.238 A x B 5 21635.744 17045.524 4575 169.139 Error 24 26065.438 10189.701 4757 265.886 * Significant at 5% level o f pro ^ability ** Significant at both 1% and 5% levels of probability 128 APPENDIX 15: EXPERIMENT 3 - FINAL HARVEST EFFECT OF TIME OF INITIATION OF MULTIPLICATION OF PLANTING MATERIAL ON VINE PRODUCTION ANALYSIS OF VARIANCE Sources of Variation Df MEAN SQUARES Percent apical vines Percent middle vines Percent basal vines Variety (A) 1 4431.50** 2879.293** 166.681** Harvest (B) 5 1917.285** 1078.980** 196.069** A x B 5 58.379 52.506 6.529 Error 24 65.665 47.020 12.269 * Significant at 5% level o f probability ** Significant at both 1% and 5% levels of probability APPENDIX 16: EXPERIMENT 3 FINAL HARVEST EFFECT OF TIME OF INITIATION OF MULTIPLICATION OF PLANTING MATERIAL ON THE DRY MATTER PRPDUCTION ANALYSIS OF VARIANCE Sources of Variation Df MEAN SQUARES Mean leaf dry weight Mean stem dry weight Mean total dry weight Variety (A) 1 19.817** 199.713** 345.353** Harvest (B) 5 16.112** 129.421** 232.502** A x B 5 4.770** 44.349** 77.641** Error 24 1.160 5.892 11.415 * Significant at 5% level of probability ** Significant at both 1% and 5% levels of probability 129