Department of Crop Science

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    Effect Of Shade On Ecophysiology Of Cocoa Under Stress Conditions
    (University Of Ghana, 2021-09) Mensah, E.O.
    Climate models predict increasing air temperature and decreasing rainfall patterns among cocoa growing regions around the world. Both heat and drought stress are known to affect physiology of cocoa plants through reduced rates of photosynthesis, lack of water and generally impaired physiological processes. This in turn leads to decreased yields and in severe cases, increased risks of mortality. Many studies have reported positive effects of shade on cocoa production; however, interest of full sun cocoa farming has been increasing over the last 20 – 40 years due to higher yields under full sun conditions with higher inputs of fertilizer. However, most of the cocoa farms in Ghana are owned by small households who cannot afford to invest into more fertilizer applications. Therefore, providing shade to buffer cocoa against erratic climatic conditions could help sustain the cocoa industry while protecting the environment. Notwithstanding, a strong debate on whether shade can buffer physiological performances of cocoa against climate change thus exists. Reports have indicated shade limiting the effects of bad weather on cocoa, but few on-farm studies have so far been done in tropical conditions to back this claim. The aim of this research was therefore to study the effects of drought and elevated temperature on performances of cocoa as a tropical understory plant and to ascertain whether shade can modify the effects. The research was carried out in two separate experiments. In experiment one, the aim was to evaluate shade on cocoa plants under different levels of water suppression. The study was conducted in a farmer’s field with 12-year-old cocoa plants. Water suppression was achieved using plastic sheets to reduce through fall to between 33% and 66%. Shade was provided with 40% black shade net raised 6.5 m over the cocoa plants. Data taken covered a period of 33 months with parameters such as chlorophyll fluorescence, water potential, photosynthesis, stem expansion and yield were monitored. In experiment two, effects of heat on physiological performances of cocoa were studied using 6- month-old cocoa seedlings. Shade was provided using 60% black shade net while air temperature 2 to 4 oC above ambient was achieved using infra-red heaters. The experiment took place in September/October 2019 wet months and was repeated in the March/April 2020 dry months. Results from experiment one confirmed the hypothesis that drought can alter physiological functions of cocoa plants and shade can be a promising strategy to modify the effects. Drought had direct effect on water status in the plant affecting plant water potential, stem expansion, chlorophyll fluorescence and photosynthesis. Cocoa plants do not efficiently regulate their stomata to conserve water under drought conditions indicating the need for a constant supply of water to the plants. Canopy density, flower production, cherelles and pods count were higher under shade conditions, however, cherelles and pod damage were a significant problem under shade. Yield in kilograms per hectare depended on season, water availability or shade varying between 90 to 1100 kg/ha/season among treatments. Shade increased yield to about 1100 kg/ha/season irrespective of the levels of water suppression while water suppression proportionally reduced dry weight yield of cocoa plants whatever the shade levels. The 2/3 water suppression plots under full sun conditions had the least yield of 286 kg/ha/season compared with same treatment under shade conditions with yield average of 431 kg/ha/season. In experiment two, shade and heat had additive effects on growth, and physiological performances of cocoa at the seedlings level. However, interactive effects of shade and heat were observed on the immediate climatic conditions of the plants; an indication that shade can modify the immediate harsh conditions around the plants. Shade increased chlorophyll fluorescence, leaf area, chlorophyll pigments of leaves and reduced leaf damage. Shaded plants revealed maximum efficient utilization of limited light available by recording lower light saturation in the range of 325 – 380 μmol m-2 s-1 and light compensation between 0 – 6 μmol m-2 s-1. Full sun plants on the other hand gave slightly higher light saturation between 427 – 520 μmol m-2 s-1 while light compensation ranged between 11 – 18 μmol m-2 s-1. Also, full sun conditions increased leaf density and stomata per unit area and rate of photosynthesis. Heat further reduced light saturation points and increased light compensation points under shade and full sun conditions. Heat affected chlorophyll fluorescence reflecting damages to photosystem II light harvesting complexes, slowing the rate of photosynthesis. Plants responded to raised heat with increased concentration of heat shock proteins (HSPs), lower light saturation points, reduced growth in height and a shift of optimal temperature for photosynthesis to higher levels to acclimate to or avoid the heat stress. Shade thus, can minimize negative effects of drought and heat on cocoa to improve yield of the plant.
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    Variability and Heterosis in Cowpea (Vigna Unguiculata (L ) Walp. ) Accessions from Four Regions of Ghana
    (University of Ghana, 1991-08) Bennett-Lartey, S.O.; Blay, E.T.; Ofori, I.; University of Ghana, College of Basic and Applied Sciences School of Agriculture Department of Crop Science
    Forty-five cowpea accessions, randomly selected from cowpea germplasm from four cowpea-growing regions of Ghana, namely, Upper East, Upper West, Northern and Eastern Regions, were characterized and evaluated at the Plant Genetic Resources Unit of the Crops Research Institute at Bunso with the objective to determine the range of variability in the samples with respect to vegetative, inflorescence and fruit characters. The variability in the samples was used to initiate hybridization among some selected accessions from the collection. Subsequently heterosis was determined for flowering and maturity dates and yield and yield components in four crosses among the selected accessions with the view to improving the yield. Large variability was observed in most of the qualitative characters, particularly growth habit, twining tendency, plant and pod pigmentation, raceme position, pod attachment to peduncle and flower colour of the germplasm. The accessions differed significantly in their days to flowering and maturity, peduncle length, number of peduncles per plant, number of pods per plant, pod length, number of seeds per plant, 100-se.ed weight and grain yield per plant. There were also significant between- aod withinregion differences I'n these characters. t Heterosis for pods per plant .and grain yield per plant in all the four crosses was positive and high. This was particularly so for grain yield per plant for the cross between accessions 87/27 and 87/157 in which heterosis was about 130%. The possibility of using accessions 87/27 and 87/157 for future improvement programmes of the crop is discussed based on their performance in this work.
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    Yield and Storability of Sweetpotato (Ipomoea Batatas (L.) Lam) As Influenced By Chicken Manure and Inorganic Fertilizer
    (University of Ghana, 2015-06) Essilfie, M. E.; Blay, E. T.; Norman, J. C.; Ofosu-Anim, J.; University of Ghana, College of Basic and Applied Sciences School of Agriculture Department of Crop Science
    Two field experiments were conducted at the Multipurpose Crop Nursery of the University of Education, Winneba, Mampong-Ashanti campus during the minor and major rainy seasons from September, 2011 to January, 2012 and April to August, 2012 respectively to verify the yield and storability of sweetpotato roots as influenced by chicken manure and inorganic fertilzer in the forest transitional agro-ecological zone of Ghana.. In both cropping seasons sweetpotato root tubers were stored for three (3) months after each harvest using three storage methods (Pit, Ash and Grass). The experimental design used for the field experiment was a 2 x 8 factorial arranged in randomized complete block design with four replicates in both studies. In the storability studies the experimental design used was a randomized complete block design with three replications. Sixteen (16) treatments were included in the field experiments. The factors under field study were two varieties of sweetpotato (i) Apomuden (Deep orange-fleshed colour with light orange skin), (ii) Okumkom (White-fleshed colour with light purple skin) and chicken manure and inorganic fertilizer (NPK) combination consisting of seven (7) organic manure and inorganic fertilizer rates and the control. In the storability studies the harvested tubers from the eight field treatments were sorted, cured and stored using the three storage methods (Grass, Ash and Pit). The results obtained revealed that the application of a combination of organic manure (chicken manure) and inorganic fertilizer for soil fertility enhancement in sweetpotato production is a better option than either organic or inorganic fertilizer applied alone. Apomuden grown on 15 – 30 – 30 kg/ha NPK + 5t/ha CM had the highest marketable and total tuber yield during the major cropping season, while Okumkom grown on 15-23-23 kg/ha NPK + 5t/ha CM and other amendments had the highest vegetative biomass (number of leaves per plant and vine fresh weight at harvest) in both seasons. Correlation analyses for both seasons showed that the vegetative growth was negatively correlated with tuber yield and market quality. However, tuber market quality was highly positively correlated with total yield of tuber. The vegetative characters were positively and significantly correlated with each other. The importance of using chicken manure and inorganic fertilizer either alone or preferably in combination as soil amendment to enhance tuber market quality at harvest, tuber nutritional composition with regard to beta-carotene, starch and sugar content over the control was clearly shown from both studies. The sweetpotato root tubers of both varieties with regard to beta- carotene, starch and sugar contents increased with manure application, especially, during the minor season. The results from both seasons clearly showed that for both varieties the pit method was the most effective storage method in terms of beta- carotene as well as starch and sugar contents over both ash and grass storage. Pit storage of Apomuden and Okumkom grown on amended and control plots resulted in improved beta-carotene, starch and sugar contents of root tuber and also stored better than ash and grass storage systems in both seasons. With regard to the cost benefit analysis Apomuden and Okumkom grown on 30-30-30 kg/ha NPK treatment dominated the other amended plots and the control in both growing seasons.
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    Genetic Analysis of Drought Tolerance in Cowpea [Vigna Unguiculata (L.) Walp]
    (University Of Ghana, 2015-12) Olubunmi, D.I.; Tongoona, T.; OFFEI, K .S Offei, S.; Blay, E.T.; Boukar, O.; University Of Ghana, College of Basic and Applied Sciences, School of Agriculture,Department of Crop Science
    Agriculture in Sub Saharan Africa (SSA) is under serious threat due to water shortage, population pressure and climate change. Cowpea, a protein-rich legume crop complements staple cereal and tuber crops in the diets of rural and urban people of the tropical and sub-tropical regions of the world. It therefore, plays a significant role in the sustainability of food and nutrition security in SSA. Cowpea, though reported to be inherently drought tolerant; but because it is mostly grown under rain-fed conditions towards the end of the rainy season in the drier parts of Nigeria, its productivity is still being adversely affected by the erratic pattern of rainfall which occurs frequently in these areas. Increasing the level of drought tolerance in existing cowpea varieties that will possess farmers’ preferred traits will increase farmers’ adoption of these varieties and ensure high and stable yield from farmers’ fields under the ever changing climatic conditions. The objectives of this study were therefore, to: (i) identify the impact of drought on cowpea production and farmers’ preferred traits in new cowpea varieties (ii) assess the diversity of cowpea germplasm for drought tolerance (iii) assess the combining ability of cowpea lines under drought and well-watered conditions and (iv) determine the gene action controlling drought tolerance in cowpea. The results of a Participatory Rural Appraisal (PRA) conducted in fifteen cowpea growing communities of Kano State, Nigeria established that drought, pests and diseases were major constraints to cowpea production. Drought reduced grain yield and fodder yield to about 62% and 56% of realizable yield under normal condition respectively. Fifty-eight percent of the farmers confirmed drought at the flowering / pod-filling stage was more devastating than drought occurring at the vegetative stage (32%) while 10% of the farmers confirmed that both growth stages were both growth stages are susceptible to University of Ghana http drought. Consumer-based traits such as large seed, short cooking time and dual-purpose varieties which increase farmers’ income were identified as important preferred traits as well as traits for biotic and abiotic tolerances in new cowpea varieties. Ninety-one cowpea varieties were screened for tolerance to drought using the wooden box screening technique with the aim to identify parents to be used for genetic analysis studies. Twenty lines were selected based on their responses to the screening and were mated in a North Carolina Design II to generate 100 single F1 crosses. The F1 progenies and their parents were evaluated under drought and well-watered conditions at two locations. Grain yield of the F1 progenies ranged between 2533 kg ha-1 for TVu6707 x TVu9797 and 18 kg ha-1 for TVu11986 x TVu2736 under drought stress, 3786 kg ha-1 for TVu6707 x TVu9797 and 45 kg ha-1 for TVu633 x TVu2736 under well-watered conditions. General Combining Ability (GCA) and Specific Combining Ability (SCA) mean squares were significant for grain yield and other traits across all research environments indicating that both additive and non-additive gene effects were important in the control of grain yield and other drought adaptive traits across all research environments. The contribution of GCA (71%) to the total sum of squares was higher than that of SCA (21%) for grain yield under drought stress indicating that additive gene action was more important in the inheritance of grain yield under drought stress. Similarly, the superior positive GCA (GCA-female and GCA-male) effects for 100-seed weight, number of seeds per pod, Normalized Difference Vegetation Index (NDVI) measured at three different growth stages, the number of pods and seeds per plant under drought stress indicated that additive gene action was more important in the inheritance of these yield related traits under drought stress. The lines TVu79, TVu6707, TVu9693 and TVu9707 were identified as general good combiners with outstanding. positive GCA effects for grain yield under drought stress. These can be used as parents to generate improved cowpea varieties for drought tolerance. Considering both mean yield and stability performance, TVu8670 x Sanzi, IT89D-288 x TVu8670, TVu6707 x TVu79 and TVu8670 x TVu79 can further be advanced for development of novel drought tolerant varieties.
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    Inheritance of Resistance to Striga Hermonthica (Del.) Benth. In An Open Pollinated Maize Population, Tzl Composite ! Cl.
    (University of Ghana, 1998-11) Akanvou, L. M. A. K.; Kling, J.; University of Ghana, College of Basic and Applied Sciences, School of Agriculture, Department of Crop Science
    The parasitic weed Striga hermonthica (Del.) Benth. of the Scrophulariaceae family constitutes one of the most economically important biological constraints in maize production in the sub-Saharan regions of Africa. The type of gene action involved in the inheritance of resistance to Striga hermonthica was investigated using the open-pollinated population, TZLComposite-1 Cl in a North Carolina design 1 scheme. Recombination were done among the best families and also the poorest performing families selected. Realized heritabilities were thus computed for important Striga related variables. This study also elucidated the rate and the extent at which resistance to Striga can be increased by using conventional population improvement methods. Comparison of the magnitude of the additive genetic variance (cr2a) and the dominance variance (a2d) showed that additive genetic variance was a major portion of the genotypic variance for characters like ear Striga rating (a2a = 0.41±0.15 and a 2d = - 0.20±0.23 ), yield of infested plants (a2a = 401564±172649 and a 2d= 571271315131), anthesis-silking interval of infested plants (a2a = 0.585±0.49 and a 2d = -0.38±0.93) and Striga rating at 8 weeks after planting (cr2a = 0.28+0.12 and c 2d= 0.03±0.21), whereas the number of Striga per host plants is controlled by non additive gene action (ci2a = 75.69±76.64 and a 2d = 211.47±134.48). Estimates of narrow-sense heritability (h2n) confirms the magnitude of the additive genetic variance in the total genetic variance for the traits ear Striga rating (h2n = 0.43+0.16), yield of infested plants (h2n = 0.31+0.13) and Striga rating (h2n = 0.33±0.15), which can be improved by selection. Estimates of realized heritability (h2 r) were highest for ear Striga rating (h2r = 0.34+0.37), yield of infested plants (h2r = 0.32±0.48) and for Striga rating (h2r = 0.27±0.57). Genetic correlations derived from the covariance of full-sib families (rg) and also genetic correlations obtained from correlated responses to selection (Rg) were estimated between the yield of infested plants and ear Striga rating (Rg = -0.50±0.38; rg = 0.88±1.28), Striga rating 1 (Rg = -0.52+0.43; rg = -0.92±0.93), Striga count 1 (Rg = -0.26±0.56; rg = - 0.22+0.46) and anthesis-silking interval (Rg = 1.76±0.09; rg = 1.05±1.30). Yield of infested plants was positively correlated to plant height of infested plants (rg = 0.61+0.54), and also to the number of ear harvested for infested plants (rg = 0.99+1.12). Anthesissilking interval of infested plants had a positive but low correlation with days to silk (rg = 0.45+0.85) and days to anthesis of infested plants (rg = 0.09+0.73). Anthesis-silking interval was negatively correlated to Striga rating at 8 weeks after planting (rg = 0.84+1.39). The results of this study indicate that resistance to Striga hermonthica in openpollinated maize varieties was shown to be controlled by polygenes . Recurrent selection (selection which involve recombination of superior genotypes to form a population for continued cyclic selection), using a selection index that includes the important traits with high level of additive genetic variance will lead to satisfactory results in selecting for Striga resistance in this open pollinated maize population.
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    Infestation of Phaseolus Vulgaris (L) By the Beanfly Ophiomyia Spp. (Diptera: Agromyzidae) and Its Management by Cultural Practices.
    (University of Ghana, 1993-04) Kayitare, J. S.; Ampong-Nyarko, K.; Ayertey, J. N.; University of Ghana, College of Basic and Applied Sciences, School of Agriculture, Department of Crop Science
    Cultural practices as management strategy for beanfly control were examined over four cropping seasons in 1991 and 1992 under farmer’s developed field conditions at Oyugis, in Homa Bay District of Western Kenya. In many parts of East and Central Africa, the beanfly is a major constraint to the production of the bean crop (Phaseolus vulgari s), its incidence causes yield losses averaging 47-87%, Control methods used against the pest are mostly insecticides based. Cultural control as a pest management strategy is a less considered area of research which needs to be studied, since it is the first line of defence against pest populations and results in little or no added cost ^ For this reason studies on five cultural practices (soil fertility, intercropping, weeding regimes, plant spacing and planting time) on beanfly infestation were undertaken as possible control methods, Increase in nitrogen levels increased beanfly infestation by 12-66%. Phosphorus served as catalyst for nitrogen assimilation. The fertilized plants were more succulent, tender and had more nutrients and therefore offered better conditions for beanfly penetration into bean stems, fecundity and development. However, the infested plants in fertilized soils were able to compensate for the damage caused to them and grew quickly to pass the critical stages. Thus the beanfly infestation had little effect on grain yield. The effect of beanfly infestation on yield when no nitrogen and phosphorus were applied, was a 48% reduction in yield, Therefore, the use of nitrogen and phosphorus fertilizers reduced the effect of beanfly damage and increased grain yield. Intercropping increased beanfly infestation compared to pure stands of beans. The microc 1imatic conditions (light intensity, temperature and relative humidity) created by intercropping of beans with maize increased beanfly infestation compared to that in the bean monocrop. Weeding regimes had no effect on beanfly infestation, however weed-free, and weeding three weeks after plant emergence, provided better grain yield, Plant spacing studies showed an increase of beanfly infestation in wider spacings. The optimal plant density of 222,222/ha (30x15 cm) seemed to give the least beanfly infestation and a high grain yield. Early planting with the first rains reduced beanfly infestation and gave better grain yield. Two species of beanfly, Ophi omyi a phaseoli Tryon and 0, spencerel1 a Greathead, were identified in Oyugis, where 0. Spencerel1 a was more predominant, Parasitoids regulated beanfly population in nature. Six species of parasitoids were identified, with Opi us phaseol i being the dominant species. They were host density-dependent and reduced beanfly population by 14-24%, The experimental results indicate that the use of nitrogen and phosphorus fertilizers, monocropping system, optimal plant density of 222,222 plants/ha and early planting time were good cultural practices that can form a part of an integrated pest management (IPM) strategy to reduce beanfly infestation with consequent increase in bean production.
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    Microsett and Slip Propagation of Dioscorea Rotundata Seed Yam
    (University of Ghana, 1987-08) Gyansa-Ameyaw, C.E.; Doku, E.V.; Hahn, S.K.; University of Ghana, College of Basic and Applied Sciences, School of Agriculture, Department of Crop Science
    The microsett technique involves the use of 2-10g setts comprising two size-ranges: a lower 2-5g and an upper 5.Ol-lOg. Preliminary experiments were undertaken to determine the ideal presprouting medium, moisture regime of the latter, presprouting environment, and sett size of the microsetts derived from the white yam variety, TDr 131. The upper 5.01-10g sett-class presprouted in open-air, raised beds covered with low palm-frond shade, using fresh sawdust at an initial moisture content of 76%, i.e. lOOOg of dry sawdust mixed with 31 of water was ideal. The acceleration and synchronisation of sprouting of the microsetts in the nursery prior to transplanting, by means of mineral nutrients were also investigated. The most practically feasible method of accelerating the sprouting of the microsetts was the tail removal technique. This involved plucking off the cormous structure bearing an apical bud from the head region of the tuber and separating the distal-1 / 3 region or tail from the head and middle portions of the tuber, herein also referred to as "head" at 3 weeks-after-harvest f (WAH). The resultant tuber parts were soaked in a nutrient mixture of 1500 parts per million (ppm) Urea, 50ppm Florel (ethephon) and lOppm Ferrous sulphate. The nutrient mixture elicited highly significant sprouting compared to the control such that at 17, 18 and 21 WAH there were no real differences between the heads and tails. The objective was to accelerate the sprouting of the tails so as to synchronize it with the heads. Consequently, microsetts from the tails could behave as heads when presprouted. The nutrient mixture application and the tail removal operation were undertaken at 3 WAH, i.e during TP I, on the bases of studies on changes in some macro- and micro-nutrient levels in the tuber with time-after-harvest. The trends in percent total nitrogen (% TN) were most spectacular : there was a decline between the 3rd and 5th weeks and a rise thereafter in the peripheral 1 .6 -1 .9cm portion of the tuber. The % TN values in the head and tail region microsetts were similar, whilst those of the middle were markedly low. These suggested a bipolar internal redistribution within the tuber. The head and tail regions of the the tuber were largely sinks, whilst the middle was largely a source. Furthermore, movement of total nitrogen was probably directed out of the peripheral 1.6 - 1.9 cm tissues into the inner ground tissues from 3 - 5 WAH and towards the periphery from the 5 WAH onwards. The nutrient mixture was thus supplied at 3 WAH on the assumption that the greatest demand for nitrogen must be at this period. The trends in % TN and hence crude protein, potassium and iron were similar. On the strength of this suggested nutrient redistribution, the tuber dormancy stage of yam ontogeny was considered as comprising a "true dormancy" sub-phase, followed by a "biochemically non-dormant tuber" sub-phase. The latter stage was assumedly indicated by the rise in % TN at 5 WAH. Consequently, the reported progressive development of the meristeiaatic layer probably starts at 5 WAH and continues till the bud on the cormous structure at the head of the tuber, becomes visibly active: the external indication that dormancy is naturally over. The slip propagation technique entails the use of the cormous structure at the head of the tuber and the associated shoot that arises from it after natural tuber dormancy release. The non-green, achlorophyllised slips derived from tubers of the white yam variety, TDr 603, stored in the dark, showed high morphogenetic ability. This was attributed to probably phytochrome-mediated responses. The direct field planting of the freshly plucked non-green slips is agroriomically ideal. A seed yam.production package based on microsetts and non-green slips is proposed.
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    The Use of Ionising Radiation from 60co Gamma Source in Controlling Mouldiness in Dried Cocoa Beans
    (University of Ghana, 2001-06) Appiah, V; Oduro, K.A; Darkwa, E.O; Yeboah, P.O; University of Ghana, College of Basic and Applied Sciences, School of Agriculture, Department of Crop Science
    Mouldiness in stored cocoa beans in Ghana and the production of aflatoxin have been studied. Based on actual weight of discarded beans, mouldy beans have been estimated to constitute 0.13 % and 0.00002 % of marketable beans at the farmers’ level and the buying agents’ depots respectively in the Tafo District. This is contrasted with an estimated value o f 0.16 % obtained in a questionnaire type study involving farmers. Estimated mouldy beans at the Tema port was 0.69 % per year (based on the cut test) representing a financial loss of $1,688,637.19 per year at S989/T should the mouldy beans be discarded. Fifty-eight (58) internally- and externally- borne fungal species were isolated from dried cocoa beans. Of these, forty-eight (48) were internally- borne and ten (10) were superficial. Twenty-nine (29) o f the internally occurring fungi have been recorded for the first time on cocoa beans in Ghana. Twenty-six (26) o f the fungi isolated belong to Aspergillus grou/?. They included A. parasiticus and A. fla vu s, which can produce aflatoxins. Five (5) belong to Penicillium, eight (8) to Fusarium and nineteen (19) to other species. Ionising radiation effectively controlled fungi associated with mouldiness in cocoa beans in a dose - dependent manner. A radiation dose o f 6 kGy completely inactivated the moulds. A. flavus and A. tamarii were the most radiation resistant moulds encountered. The moisture content o f the beans before, during and after irradiation influenced the effect of radiation. The relative humidity during storage and the type o f packaging also influenced the radiation effect. Conidia of-A fla vu s subjected to moist heat at temperatures 20 °C to 60 °C for 2.5, 5 and 10 min respectively were not significantly affected by heating up to 50 °C. Pleating an aqueous conidial suspension at 60 °C for at least 2.5 min reduced the number of fungal colonies by at least 5 log cycles when the suspension was assayed on agar plate media. Heating at 59 °C for 10 min completely inactivated the wet conidia of A. flams. When a combination o f moist heat and radiation was applied to A. flavus, in different media, the inactivation dose was different in each medium. In vitro studies on A. flavus in suspension showed that the fungus could be inactivated by applying a combination o f moist heat at 50°C for 10 min followed by 1.0 kGy radiation. A combination of moist heat at 80 °C and radiation at 3.5 kGy produced the same effect with cocoa beans. Storage o f beans for 28 days at 75% RH suppressed fungal growth while storage at 90% RH resulted in mouldiness o f beans previously inoculated with A. fla m s conidia and treated with heat and radiation. No aflatoxin was detected in cocoa beans after 4 weeks following inoculation with conidia of a toxigenic A. f la w s strain and irradiation at 10 kGy. Without irradiation, inoculated beans became mouldy and produced aflatoxin Bi. Irradiation at 10 kGy could not destroy the already formed aflatoxin. Radiation up to 6 kGy gave cocoa butter with free fatty acid, melting point, saponification value, and unsaponifiable matter levels comparable with factory standards. Exposure of beans to radiation did not have any effect on the rancidity o f the extracted cocoa butter. Exposure of beans to radiation only or to radiation after heat treatment also did not affect the rate at which cocoa butter solidified. No significant differences in taste, colour and flavour were detected in cocoa drink prepared from cocoa powder produced from irradiated beans.
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    Deployment of the cowpea aphid resistance gene for cowpea improvement in Ghana
    (University of Ghana, 2014-07) Kusi, F.; Asante, S.K; Padi, F.K; Obeng-Ofori, D.; University of Ghana, College of Basic and Applied Sciences, School of Agriculture, Department of Crop Science
    Resistance to the cowpea aphid is important component of integrated pest management of cowpea cropping systems most especially at the vegetative stage. The objective of this study was to demonstrate the effectiveness of the aphid resistance locus identified in advanced breeding line SARC 1-57-2 in reducing damage from the cowpea aphid in Ghana. Using an F2 population developed from Apagbaala x SARC 1-57-2, the resistance locus was tagged with the SSR marker CP 171F/172R with a recombination fraction of 5.91%. Based on the CP 171F/172R, recurrent marker assisted backcrossing was carried out to introduce the resistance locus into the susceptible cultivar, Zaayura. This led to the development of several BC4F3 lines that are isogenic except for the region of the resistance locus. In field tests under no insecticide protection, the BC4F3 lines carrying the dominant marker allele suffered 3% loss of biomass and 4% loss of grain yield compared with plots protected with recommended insecticides. The BC4F3 lines carrying the recessive marker allele recorded 12% loss of biomass and 33% reduction in grain yield compared with the sprayed plots. The resistance locus did not influence the number of days to flowering or maturity and no pleiotropic effects were observed in terms of plant morphology or seed characteristics. In all segregating populations analysed, the locus segregated as a single Mendelian gene. Stability of the resistance locus was conducted at 18 locations covering six important cowpea growing Regions in Ghana. The range of damage by the pest on resistant and susceptible progenies were consistent across locations, and did not support the hypothesis of existence biotypes of the insect (based on differences in feeding damage on different varieties) in Ghana. This stability in performance places a premium on the resistance locus in improving cowpea cultivars developed for different agro-climatic regions of the country for resistance to the pest. The study has demonstrated the effectiveness of an insect resistance locus in significantly reducing insect damage under typical cowpea production conditions in Ghana