INFLUENCE OF TEMPERATURE ON THE YIELD AND QUALITY OF THREE STRAWBERRY ( Fragaria * anannasa Duch) CULTIVARS This Thesis is submitted to; Department of Crop Science College of Agriculture and Consumer Sciences University of Ghana By PATRICK MIREKU (10327810) In partial fulfillment of the Requirement for the Award of MASTER OF PHILOSOPHY DEGREE In CROP SCIENCE MARCH, 2012 University of Ghana http://ugspace.ug.edu.gh i University of Ghana http://ugspace.ug.edu.gh ii ABSTRACT The influence of temperature on yield and quality of three Japanese strawberry ( Fragaria x anannasa Duch) cultivars („Sachinoka‟, „Benihoppe‟ and „Tochiotome‟) were studied between March and August, 2011 in a screen house at Tokyo University of Agriculture and Technology, Japan. Completely Randomised Design was used with eight (8) replications each of the cultivars. One set of treatment comprising of the three cultivars were set as control and the other treatment was set under a thin film of shade. Yield parameters taken included fruit length, fruit weight, fruit width and number of fruit harvested per plant. Quality parameters taken were fruit colour and fruit firmness. Few vegetative growth parameters were also recorded and these included leaf length and leaf area. The optimum day/ night temperature for fruit development, fruit length, fruit width and fruit weight was 26/14 ºC, which occurred in the month May. However, the above parameters reduced as temperature increased throughout the study period. Further, fruit firmness decreased as the temperature increased throughout the study period. Fruit surface colour L, which indicates „lightness of colour‟ became darker and greater in pigment intensity as temperature increased to 34/23 ºC in July. Increasing growth temperatures resulted in smaller leaf area whiles leaf length increased. Chlorophyll content of leaves and light interception by plants in screen house also increased as the University of Ghana http://ugspace.ug.edu.gh iii growth temperature increased. Increasing growth temperatures of the environment resulted in decreased fruit quality including soluble solids. However, sugar-acid ratio, titratable acids and pH varied among the cultivars indicating that these qualities may be heritable traits as they were less influenced by the environment. University of Ghana http://ugspace.ug.edu.gh iv ACKNOWLEDGEMENT I am grateful to the almighty God for how far he has brought me. I also take this opportunity to thank Prof. Ogiwara for allowing me to use his laboratory whiles I was undertaking my research work in Japan. I am also grateful to the students of the Horticultural Laboratory, Tokyo University of Agriculture and Technology for their support and cooperation during my stay in their laboratory. I am deeply grateful to Prof. John Ofosu-Anim and Prof. Ogiwara Isao, my supervisors for their motivation, constructive criticisms and their guidance in the preparation of this work. Sincere gratitude is also extended to Doctor Onwuna Agyemang of the English Department, Tokyo University of Agriculture and Technology for his support whiles I was undertaking my research in Japan. My deepest appreciation also goes to my parents, four sisters, Vera, Mirander, Lydia and Doreen for their motivation and support during my study. I would like to also express my sincere thanks to all my course mates for the ir cooperation and advice. University of Ghana http://ugspace.ug.edu.gh v DEDICATION I dedicate this thesis to my parents who always supported me both financially and spiritually and helped me to climb up the academic ladder. University of Ghana http://ugspace.ug.edu.gh vi TABLE OF CONTENTS TITLE PAGE DECLARATION …………………………………………………………………………………..i ABSTRACT ................................ ................................ ................................ .................................... ii ACKNOWLEDGEMENT ................................................................ ................................ .............. iv DEDICATION ................................ ................................ ................................ ................................ v TABLE OF CONTENTS ................................................................ ................................ ............... vi LIST OF TABLES ................................ ................................ ................................ .......................... x LIST OF FIGURES ................................................................ ................................ ........................ xi LIST OF ACRONYMS ................................................................ ................................ ................ xiii CHAPTER ONE ................................ ................................ ................................ .............................. 1 1.0 INTRODUCTION ................................................................ ................................ ..................... 1 CHAPTER TWO ................................ ................................ ................................ ............................. 5 2.0 LITERATURE REVIEW ................................ ................................................................ .......... 5 2.1 Sachinoka ................................ ................................ ................................ .................................. 5 2.2 Tochiotome ................................ ................................ ................................ ................................ 6 2.3 Benihoppe ................................ ................................ ................................ .................................. 6 2.4 Light and temperature effects on the flower initiation and growth of strawberry ..................... 7 2.4.1 Photoperiod response of strawberry ................................ ................................ ....................... 7 2.4.2 Light intensity and quality ................................ ................................................................ ...... 8 2.5 Temperature ................................ ................................ ................................ ............................. 10 2.5.1 Temperature interaction with photoperiod ................................ ................................ ........... 11 University of Ghana http://ugspace.ug.edu.gh vii 2.5.2 Thermoperiod and flower induction ................................ ................................ ..................... 13 2.5.3 High temperature and flower induction ................................ ................................ ................ 14 2.5.4 Low temperature and flower induction ................................ ................................ ................ 14 CHAPTER THREE ................................................................ ................................ ....................... 17 3.0 MATERIALS AND METHODS ................................ ................................ ............................ 17 3.1 Plant material and treatments used ................................ ................................ .......................... 17 3.2 Mean fruit length, mean fruit weight, fruit width, petiole length (Leaf height), leaf width and leaf area ................................ ................................ ................................................................ ......... 20 3.3 Relative Chlorophyll content ................................ ................................................................ ... 20 3.4 Temperature, humidity and light intensity ................................ ................................ .............. 21 3.5 QUALITY MEASUREMENT ................................ ................................ ................................ 22 3.5.1 Fruit Firmness ................................................................ ................................ ....................... 22 3.5.2 Colour measurement ................................................................ ................................ ............. 23 3.5.3 Preparation of samples for chemical measurement ................................ .............................. 24 3.5.4 Soluble solids (SSC), pH and Titratable acids (TA) ................................ ............................ 25 CHAPTER FOUR ................................ ................................ ................................ ......................... 27 4.0 RESULTS ................................ ................................ ................................ ................................ 27 4.1 TOTAL NUMBER OF FRUITS HARVESTED DURING THE STUDY ............................. 27 4.2 Fruit weight ................................ ................................ ................................ ............................. 28 4.3 Fruit length ................................ ................................ ................................ .............................. 29 4.6 Leaf area ................................ ................................ ................................ .................................. 33 4.7 Chlorophyll content ................................................................ ................................ ................. 35 University of Ghana http://ugspace.ug.edu.gh viii 4.8 Light intensity ................................ ................................ ................................ .......................... 36 4.9 Temperature ................................ ................................ ................................ ............................. 37 4.10 Humidity ................................ ................................ ................................ ................................ 38 4.11.1 Fruit firmness ................................................................ ................................ ..................... 39 4.11.2 Fruit colour ................................ ................................ ................................ ......................... 40 4.11.3 Soluble solid content ................................ ................................................................ .......... 41 4.11.4 Titratable acidity ................................................................ ................................ ................. 42 4.11.5 Sugar:acid ratio ................................................................ ................................ ................... 43 4.11.6 Percentage acidity ................................................................ ................................ ............... 44 4.11.7 pH ................................ ................................ ................................................................ ....... 45 CHAPTER FIVE ................................ ................................ ................................ ........................... 46 5.0 DISCUSSION ................................ ................................ ................................ ......................... 46 5.1 Effect of temperature on total number of fruits/ plant ................................ ............................. 46 5.2 Effect of temperature on fresh fruit weight, fruit length and fruit width ................................. 47 5.3 Effect of temperature on leaf area and leaf height of strawberry cultivars used in the study .. 48 5.4 Light intensity ................................ ................................ ................................ .......................... 49 5.5 Chlorophyll ................................ ................................ ................................ .............................. 50 5.6 Fruit firmness ................................ ................................ ................................ .......................... 51 5.7 Fruit colour ................................ ................................ ................................ .............................. 52 5.8 Total soluble solids (TSS) and sugar: acid ratio ................................................................ ...... 53 5.9 Titratable acidity, percentage acidity and pH ................................................................ .......... 54 University of Ghana http://ugspace.ug.edu.gh ix 6.0 CONCLUSION AND RECOMMENDATIONS ................................................................ .... 56 6.1 CONCLUSION ................................................................ ................................ ....................... 56 6.2 RECOMMENDATIONS ................................ ................................................................ ........ 58 REFERENCES ................................ ................................ ................................ .............................. 59 APPENDIX ................................ ................................ ................................................................ ... 70 University of Ghana http://ugspace.ug.edu.gh x LIST OF TABLES Table 1 : Total number of fruits harvested . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7 Table 2 : E ffect of shade on mean fruit weight (mm) of the three ( 3 ) strawberry cultivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 8 Table 3 : E ffect of shade on mean fruit length (mm) of the three strawberry 2 9 Table 4 : E ffect of shade on mean fruit width of the strawberry cultivars . . . . . 3 1 Table 5 : E ffect of shade the mean leaf height (cm) of the three strawberry cultivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Table 6 : E ffect of shade on the mean leaf area (cm² ) of the three strawberry cultivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Table 7 : Variation in Chlorophyll content of the three strawberry cultivars . 3 5 Table 8 : E ffect of shade on the mean fruit firmness ( kg ) of the strawberry cultivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 9 Table 9 : Fruit colour measurement of the strawberry cultivars used in the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 0 Table 1 0 : E ffect of shade on the total Soluble Solid Content ( % ) of the three strawberry cultivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1 Table 1 1 : E ffect of shade on titratable acidity (mls ) of the strawberry cultivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 Table 1 2 : E ffect of shade on Sugar acid ratio of the three cultivars . . . . . . . . . . . . 4 3 Table 1 3 : E ffect of shade on the Percentage ( % ) acid content of the three strawberry cultivars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 Table 1 4 : E ffect of shade on pH of the strawberry cultivars used . . . . . . . . . . . . . . . . 4 5 University of Ghana http://ugspace.ug.edu.gh xi LIST OF FIGURES Figure 1 : Control plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 9 F igure 2 : P lants under shade treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 9 F igure 3 : Chlorophyll meter ( Model SPAD - 5 0 2 , M inolta, Japan ) used for measuring leaf chlorophyll during the experimental period . . . . . . . . . . . . . . . . . . . . . . . . 2 1 F igure 4 : Penetrometer ( Fudoh Rheometer RT - 3 0 0 5D ) used for measuring fruit firmness during the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 F igure 5 : Calorimeter ( M inolta, Model CR - 3 0 0 , Osa ka , Japan) used for measuring fruit colour during the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 F igure 6 : F ruit samples for chemical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 F igure 7 : Ground fruit samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 F igure 8 : Centrifuge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 F igure 9 : p H meter (p H - 5 2 6 ; WT W measurement systems, W issenschaftlich - Technische Wer kstatten GmbH , Wellhelm, Germany) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 5 F igure 1 0 : Refractometer ( Palette 1 0 0 PR - 1 0 0 , AT AGO -Spectrum Technologies , P lainfield,I L ) used for measuring bri x during the experimental period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 5 F igure 1 1 : Light intensity variation measured during bright days at two hour interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6 F igure 1 2 : Light intensity variation measured on sunny days at two hour interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6 F igure 1 3 : Temperature variation measurements during the experimental period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7 University of Ghana http://ugspace.ug.edu.gh xii Figure 1 4 : Humidity measurement during the experimental period . . . . . . . . . . . . . . 3 8 University of Ghana http://ugspace.ug.edu.gh xiii LIST OF ACRONYMS SYMBOL MEANING ºC Degree Celsuis          Micro mol Mole per meter square per second PAR Photo synthetically Active Radiation mls Milli litres % Percentage TSS Total Soluble Solids Kg Kilogram mm Mi llimeter cm Centimeter cm² Centimeter squared S.A.S Statistical Analysis System g gram SPAD Single Photoelectric Analysing Diode N Newton University of Ghana http://ugspace.ug.edu.gh 1 CHAPTER ONE 1.0 INTRODUCTION Strawberry (Fragaria x ananassa Duch.) belongs to the Rosaceae family. It is cultivated in at least 63 countries worldwide. The total world production and acreage are estimated at 2,700,000 MT and 200 , 000 ha, respectively. The United States is the largest strawberry producing country with almost 28% of total world production (FAO, 1997) . The cultivated strawberry, Fragaria x ananassa , fruits form a regular part of the diets of millions of people. Strawberries have been shown to be a rich source of phenolic compounds with antioxidant and anti-proliferation activities (Wang et al., 1996). The strawberry is widely considered as a high value crop because of the high demand. The fruits are rich in vitamin C, iron, potassium and fibre. Strawberries have also been credited with cancer-fighting compounds (Stoner et al ., 1999). For hundreds of years homeopathic practitioners have incorporated strawberry plants and fruits in the treatment of anaemia, diabetes, rheumatic gout, kidney and liver complaints. Fresh strawberry removes tarter and teeth stains, soothes sunburn and lightens freckles. Strawberry preserves and jellies are widely used worldwide (Broom et al ., 1987). Wang et al. (1996 ) and Eberhardt et al. (2000 ) have shown that the major antioxidant activity in fruits or vegetables may originate from the polyphenolic compounds and that total phenolic content (TPC) is the major contributor for their antioxidant activities. University of Ghana http://ugspace.ug.edu.gh 2 Polyphenolic compounds display important functions in plant defence mechanisms and external stresses (Tao et al., 2010) which helps in extending the shelf life and also enhancing the quality of preservation of fruits by delaying senescence induced by oxidative degradation ( Connor et al., 2002). Polyphenolic compounds also affect the quality, colour and taste of fruits (Robarbs et al., 1999). Tao et al. (2010 ), Hebert et al. (2002 ) and Khanizadeh et al. (2008 ) also observed from their respective studies that Strawberry cultivars, rich in proanthocyanidins, are more resistant to fungal attacks by Botrytis cinerea, even though no strawberry cultivar is completely resistant to that fungus. Herbert et al. (2002 ) also suggested that proanthocyanidin content can be used as an indicator of grey mold resistance, in order to screen strawberry selections and cultivars for improving shelf life and quality. Genetic factors affect strawberry plant growth and development as well as composition of the fruit. However, strawberry plants are also highly sensitive to variation in environmental conditions. Factors such as water availability, day and night time temperatures, and daylight intensities affect fruit size (Avigdori-Avidov, 1986). Strawberry cultivars grown in specific areas are often adapted to the growing conditions of that area. Nevertheless, temperature stress is one of the challenges facing strawberry production in the world. Field grown plants are often subjected to fluctuating temperature that has a profound effect on the plant metabolism ( Chaitanya et al., 2001). University of Ghana http://ugspace.ug.edu.gh 3 Reduction in plant growth by high temperatures is well established in horticultural crops such as tomato ( Solanum lycopersicum L.) (Adams et al., 2001), grape ( Vitis spp) (Chaumont et al., 1997), and strawberry (Renquist et al., 1983). Generally, exposure to high temperature (35ºC) results in reduced plant growth (Hellman and Travis, 1988) and lowers yields (Hellman and Travis, 1988) . High temperatures adversely affect vegetative growth and fruit quality of tomato ( Adams et al., 2001; Mulholland et al ., 2003) and reproductive systems of peanut ( Arachis hypogaea L. ) (Vara- Prasad et al., 1999). There have been several reports on the responses of strawberry to various temperature regimes. It was observed by Zang et al. (1997) that strawberry cells subjected to 30ºC grew slowly and failed to proliferate normally in suspension cultures. Strawberry vegetative growth (Hellman and Travis, 1998), root growth (Fukuda et al., 1988 ), fruit set (Nishiyama et al., 2003), pollen viability (Ledesma et al., 2005), fruit weight (Mori , 1998) and fruit quality (Polito et al., 2002) were all reported to be negatively affected by high temperatures. However, some strawberry plants resistant to high temperature have the ability to maintain high rate of photosynthesis, stabilize proteins and also synthesis new proteins (Gulen and Eris , 2004). Inspite of the negative effects temperature has on strawberry growth and development, strawberries are cultivated in all arable regions of the globe from the Arctic to the Tropics (Hancock, 1998 ). Pipattanawong (1996 ) reported that the June- bearing „Tioga‟ is adaptable to the high elevation environments in Thailands and produced appreciable marketable fruit sizes. Hellman and Travis (19 98 ) established that the critical range of University of Ghana http://ugspace.ug.edu.gh 4 strawberry growth inhibition is between 35 and 40 ºC and also development of runners is reduced significantly by a three ( 3) day exposure to 40 ºC of temperature. However, the mechanisms involved in heat stress as well as information related to strawberry varietal response to heat stress on the yield and quality of strawberry fruits is limited. An annual temperature fluctuation occurs in Japan from late spring to the end of summer; a period characterized by high temperature and long exposure to day light that severely impact negatively on the growth and productivity of strawberry. High temperature is anticipated to become a limiting factor to strawberry growth in the future as well as many plant species, as global warming increases. Therefore, research on the mechanism of high temperature stress in strawberry has importance for future advances. The objective of this study was to determine the effect of high temperatures and shade on yield and quality of three Japanese strawberry cultivars. University of Ghana http://ugspace.ug.edu.gh 5 CHAPTER TWO 2.0 LITERATURE REVIEW Growth characteristics, origi n and morphorlogical descrip tion of Sachinoka, Tochioto me and Benihoppe straw b erry cultivar s. 2.1 Sachinoka The cultivar „Sachinoka‟ was registered as Strawberry Norin No. 20 in 1996 and was developed as a variety for fresh market in forcing culture. The plant is moderately prostrate and the peduncle is slightly longer. Thus intensive management including manual positioning of leaves to expose fruits to light and spraying of gibberellic acid to elongate the flower stalk is not necessary to accelerate fruit colouring. The flower bud of the terminal cluster becomes differentiated in the middle of September under natural conditions. Under forcing conditions, lateral fruit clusters are formed continuously and the plants do not tend to become dwarf even in mid-winter. Early and total fruit yield in normal forcing culture is almost the same as in „Toyonoka‟ The yield until late December is with night cooling and short day treatment in summer before transplanting is 50 to 100% that of „Toyonoka‟, while the total yield until spring is almost the same. Average fruit size is slightly smaller but larger than that of „Nhoyo‟, the leading variety in forcing culture in Eastern Japan. The fruit skin is shiny scarlet and the shape of the fruit is uniformly conical. Since the fruit firmness is about 20% than that of „Toyonoka‟ and „Nyoho‟, handling efficiency after harvest and transportability over long distances is higher. The fruit contains a large amount of sugar and ascorbic acid and the flesh texture is suitable for fresh consumption. Sachinoka is susceptible to antracnose, fulsarium wilt University of Ghana http://ugspace.ug.edu.gh 6 and powdery mildew but symptom severity and spread of powdery mildew are apparently less severe than other strawberry cultivars. „Sachinoka‟ is adapted to forcing culture which is especially useful for large scale growers who need labour-saving practices and for production areas rather far from the market where long distance transportation is required. Source; Journal of the Japanese Society for Horticultural Science, 1994. 2.2 Tochiotome „Tochiotome‟ is a new strawberry cultivar released in Japan in 1996. It was selected from hybrid seedlings of a cross between „Kurume 49‟ (Toyonoka /Nyoho) and „Tochinomine‟ (Kei511/Nyoho) crossed in 1990 to obtain high performance cultivar for forcing culture in Tochigi prefecture, Japan. Tochiotme is vigorous and produces runners well. The leaves are large and dark green and the degree of dormancy is simi;lar to „Nyoho‟, the most popular cultivar for forcing culture. The number of flowers per inflorescence is fifteen on the average. The yield is higher than „Nhoho‟. The fruits are conical in shape and have very shining scarlet colour. They have firm peel and flesh so the storage quality is very high. They have strong aroma, week acidity and are also very juicy making the taste excellent. They are slightly resistant to powdery mildew. Source; Journal of the Japanese Society for Horticultural Science, 1994. 2.3 Benihoppe The cultivar „Benihoppe‟ was obtained by crossing „Akihime‟ and „Sachinoka‟. The time of flower bud initiation is later than „Akihime‟ but the secondary and tertiary fruit University of Ghana http://ugspace.ug.edu.gh 7 clusters are formed continuously. Plant growth is vigorous with successful runner production. The fruit texture is firm making it more suitable for transport and preservation. The fruits contain high sugar and moderate acid content corresponding to that of Sachinoka cultivar. These factors as well as its strong fragrance make the taste very excellent. Average fruit size is larger than other strawberry cultivars but the number of fruits per plant is very few as compared with the other cultivars. Benihoppe is susceptible to Antracnose and powdery mildew. Source; Journal of the Japanese Society for Horticultural Science, 1994. 2.4 Light and temp erature ef f ects on the flow er in itiation and grow th of straw b erry 2.4.1 Photoperiod resp on se of straw b erry Photoperiod is a primary environmental factor controlling the transition from vegetative to reproductive growth in strawberry. Commercial strawberry ( Fragaria x ananassa Duch.) cultivars are classified as short -day or day-neutral, depending upon plant response to photoperiod for flower induction (Durner et al. , 1984). There is a third group of cultivars known as long-day or everbearing that had relative importance in the past, but is not currently produced commercially. As reviewed by Darnell and Hancock (1996), in general terms short day genotypes initiate flowers when photoperiod is shorter than 14 hours. On the other hand, day-neutral genotypes seem to be independent of day length in initiating flowers. For example, studies done by Durner et al. (1984) on the day-neutral types „Hecker‟ and „Tristar‟ showed that the numbers of inflorescences per plant were not significantly different under photoperiods of 9 hours (short -day) or 16 hours (long-day ). University of Ghana http://ugspace.ug.edu.gh 8 Optimum photoperiod and number of inductive cycles necessary for most plants to flower are temperature and cultivar dependent. However, as other cultivars have progressively been included in flowering studies, the photoperiodic range for flower induction became even wider suggesting that the response to photoperiod is cultivar related. Temperature is another factor to be considered when studying photoperiodic responses in strawberry and will many times interact with photoperiod to induce the response. A third factor affecting photoperiodic response is the previous conditioning of the plant (i.e. chilling temperatures). Additionally, the age or size of the plant might condition the perception of light and temperature when photoperiods and/or temperatures are not optimum for flower induction. The older (or larger) the plant, the greater the sensitivity to photoperiod and temperature. Several literatures found that the exposure of only one leaf to light is enough to induce developmental responses in a plant grown under optimum floral inductive conditions. Generally, success in conditioning plants requires plants actively growing during the inductive treatment, as suggested by Nishizawa et al . (1997). 2.4.2 Light inten sity and quality Manipulation of flowering in strawberry by different light intensities and quality has been broadly reported in literature. In Belgium, when light from mercury lamps with an intensity of 300 mol was added to the natural winter light (to improve ligh t efficiency in the PAR region) a gain in earliness (10-15 days) of fruit production was achieved in Fragaria x ananassa Duch. „Primella‟ (Ceulemans et al. , 1986 ). Truss length, University of Ghana http://ugspace.ug.edu.gh 9 petiole length, and leaf area were also increased under this light treatment. Under high light intensity (650 mol ) provided by incandescent, improved mercury vapour and sodium vapour lamps, the wild strawberry Fragaria vesca produced significantly more flowers per plant than at lower light intensities (22 or 150  ) (Chabot, 1978). Dennis et al. (1970) reported that an intensity of ~430  fluorescent + incandescent light almost doubled the number of flower stalks per plant compared to ~220  in „Geneva,‟ a day neutral strawberry, under long photoperiod or continuous light, and at 24°/21°C. In the UK, Wright and Sandrang (199 5) observed a reduction in crown number in „Hapil‟ strawberries when the percentage of shading on the plant was increased from 0 to 70%. Although flowering and fruiting were not evaluated in that experiment, which was conducted from May to Sept., the authors suggested a potential decrease in yield in plants grown under >25 % shade as a consequence of decreased crown branching. Flower initiation in short -day strawberries may be regulated by light quality and the phytochrome (P) may be involved in the flowering process (Collins, 1966; Vince-Prue and Guttridge, 1973 ). Vince- Prue and Guttridge (1973) exposed „Cambridge Favourite‟ (short-day) plants to 8, 14, and 17 cycles of 8 hour photoperiod, and to 20 -21°/15 -16°C day/night temperatures. The 8-h our photoperiod was extended to 16.5 hours with red (fluorescent light), far red (incandescent light) or a 1:1 ratio of red and far red lights. After completion of the light treatments, the plants were grown under long day (24 - h photoperiod) for 2 weeks. Then the plants were dissected in order to examine floral primordia formation. Eighty percent control plants (grown under an 8-h photoperiod without light extension) flowered after 14 short-day (8 h) cycles. Photoperiod extension University of Ghana http://ugspace.ug.edu.gh 10 with far red retarded floral initiation (only 20% plants flowered after 17 short-day cycles). Photoperiod extension with red far red decreased floral initiation (40% plants flowered after 14 short-day cycles). Photoperiod extension with red light did not delay floral initiation (60% plants flowered after 14 short-day cycles). According to Vince-Prue and Guttridge (1973 ), photoperiod extension or night-break with a high red/far red ratio (which increases Pfr or far-red absorbing form of the phytochrome), given during the long dark period required for flowering in short-day plants, suppressed flowering in short -day species such as Perilla , and Xanthium. On the contrary, photoperiod extension with a high red/far red ratio did not inhibit flowering in short-day strawberries. Therefore, they suggested that rather than the phytochrome reactions, other mechanism, such as the production of a flower inhibitor in the leaves, might prevent flowering in short- day strawberry plants grown under long photoperiod. 2.5 Tempe rature Temperature is an important factor influencing seed germination, vegetative growth, flowering, fruit set and fruit ripening in horticultural crops (Sage and Kubien, 2007; Ledesma et al ., 2008; Kositsup et al ., 2009). Both high and low temperatures, be they temporary or constant, can induce morpho-anatomical, physiological and biochemical changes in plants, leading to profit reduction (Higuchi et al ., 1998; Wang et al ., 2003; Wahid et al ., 2007). Heat stress can be a concern in many regions of the tropics and subtropics, since high temperature can cause significant damage such as sunburns on University of Ghana http://ugspace.ug.edu.gh 11 leaves, branches and stems, anticipated leaf senescence and abscission, shoot and root growth inhibition and fruit discoloration and damage (Yamada et al ., 1996; Higuchi et al ., 1998; Almeida and Valle, 2007; Wahid et al ., 2007). Temperature conditions the response of Fragaria to photoperiod in short-day and day- neutral cultivars. Temperature is considered as important as photoperiod for flowering at high latitudes where long photoperiods prevail (Heide, 1977), and in tropical to equatorial latitudes, where photoperiod is short enough for flowering year round but where temperatures are too high. For this reason, in equatorial regions, strawberry can be commercially grown only in the highlands, where temperatures are lower. The development of cultivars adapted to both extremes of latitude has allowed the expansion of the cultivated species in these areas. 2.5.1 Tempe rature inter action w ith photoperiod Series of experiment have led to the conclusion that short-day strawberry cultivars are temperature related. Consequently, these plants have been classified as short day- qualitative or absolute plants at high temperature, and short day quantitative or facultative at low temperature (Salisbury and Ross, 1992). Darrrow (1966) exposed nine different strawberry cultivars to three photoperiods combined with three different temperature regimes. He found out that those photoperiods less than 14 hours combined with temperatures around 15°C produced the best flowering response. Thus , the longer the photoperiod, the lower the temperature needed to maximize flower number. Conversely, University of Ghana http://ugspace.ug.edu.gh 12 environments with long photoperiod and relatively high temperature minimized flower induction and promoted vegetative growth. Evidence supporting Darrow‟s results has been continuously produced by several scientists. Hartmann (1947a, b) exposed plants of several cultivars to two temperatures (15.5°C and 21°C) and two photoperiods (10 and 15 hours). All plants were induced to flower at 15.5°C, regardless of the photoperiod. Ito and Saito (1962) reported that „Robinson‟ was induced to flower at temperatures between 9°C and 24°C, and 8 h our photoperiods. Jonkers (1965) obtained mor e flowers at 15°C than at 21°C in „Talisman‟ in a short photoperiod, but failed to induce blossoms at 15° C. Heide (1977) compared the interactions of three temperatures (12°C, 18°C, and 24°C) and five photoperiods (10 hours, 12 hours, 14 hours, 16 hours and 24 hours) in five cultivars. At 12°C and 18°C, three cultivars flowered at all photoperiods, but they remained vegetative at 24°C under long photoperiod. In the other cultivars, critical temperatures were 12°C at 16 hours , 18°C at 14 hours, and 24°C at 13 h ours photoperiod. Went (1957) exposed the short day cultivar „Marshall‟ to four temperatures (6°C, 10°C, 14°C, and 20°C) and three photoperiods (8 hour, 16 hour, and 24 hours). Plants initiated flowers at all temperatures under an 8h photoperiod. Plants under a 16 h our photoperiod flowered only at 6°C or 10°C. Went therefore defined „Marshall‟ as a short day cultivar at temperatures above 10°C and day neutral cultivar at lower temperature since they flowered even under a 24 hour photoperiod. University of Ghana http://ugspace.ug.edu.gh 13 Sonsteby (1997) reported that at 9 Cor 15 C, the short day cultivars „Bounty‟ and Sengana‟ flowered under both 8 hour and 24 h our photoperiods. It was concluded that flowering in plants grown under 9 C-15 C was photoperiodically insensitive. Collins and Barker (1964 ) induced „Sparkle‟ to flower under relatively high temperatures (23 C /20 C) and continuous light, simply by changing light quality during the 20 C period. Thus, photoperiod/temperature interactions are likely to influence the flowering response at mid range temperatures (15 - 25 C), although the specific response is cultivar dependent (Sonsteby, 1997). The minimum number of inductive cycles is a measure of the efficiency of the photoperiod and temperature interaction to bring about flower induction. At a10 hour photoperiod and 21°C, „Missionary‟ required 4 to 7 inductive cycles to start flowering, although this cultivar expressed maximum flowering with 21 cycles (Hartmann, 1947b). Went (1990 ) found that at 17° C to 23°C, 9 to 15 short day cycles were needed to induce flowering in „Marshall.‟ Ito and Saito (1962) established that 10 cycles of 9°C with photoperiods between 8 hour and 12 hour brought about floral induction in a short day cultivar. „Sparkle‟ was induced in 12 to 15 days under an 8 -h photoperiod combined with 21° C /18°C day/night temperatures (Moore and Hough, 1962 ). 2.5.2 Thermop e riod and flow er in duction Hartmann (1947a) showed that „Missionary‟ plants conditioned with short photoperiods and fluctuating day (26. 7 C) and night (15.6 C) temperatures had earlier fruit set and ripening than those grown at a constant temperature of 21 C. No differences in the total number of flowers were observed. Okimura and Igarashi (1997), found no difference University of Ghana http://ugspace.ug.edu.gh 14 between 25 C/15 C (day/night) and 20 C constant in terms of flower induction the cultivar „Selva‟ grown under a 16 hour photoperiod. Fluctuating temperatures have been used in experiments designed to promote flower induction in the cultivated and wild strawberries (Reichart, 1973; Bish et al ., 1997; Durne r et al. , 1984; Chabot, 1978). 2.5.3 High temp e rature and flow er induction Durner and Poling (198 8) revealed that flowering is inhibited by high temperature in short-day genotypes and these genotypes are more sensitive than day-neutral genotypes. Regardless of the photoperiod, constant high temperatures in the range of 28°C to 30°C inhibited flower induction in short day and day neutral cultivars of F. x ananassa Duch., and in F. vesca (Okimura and Igarashi, 1997). Heide (1977) found that flower number decreased considerably when plants of „S. Sengana‟ and „Abundance‟ were exposed to 24°C under short photoperiods, compared to 18°C. „Sweet Charlie‟ plug transplants grown at a 25/15°C day/night temperature regime initiated flowers earlier and developed a more profuse root system than those held at 35/25°C under identical photoperiod and time of exposure (Bish et al. , 1996 ). Heide again stated that high temperature acts synergistically with long-days in promoting the biosynthesis of a flower inhibitor. 2.5.4 Low temp era ture and flow er induction Several reports have indicated that lower temperatures are very necessary for flower induction. Low temperature in strawberry is related to chilling; a variable period of University of Ghana http://ugspace.ug.edu.gh 15 exposure to temperatures below 10°C that breaks bud dormancy. Darnell and Hancock, (1996) reported that chilling in strawberry plants was reported to promote both reproductive and vegetative responses, and was an important factor in balancing reproductive and vegetative growth. Chilling enhances vegetative growth, reduces flower induction, does not affect flower initiation, but augments floral differentiation (Durner and Poling, 1987). Increases in petiole length, leaf size, leaf number, leaf area, and runner formation occur as chilling increases (Kahangi et al. , 1992; Lieten, 1997 ) . The chilling requirement is cultivar dependent in F. x ananassa Duch probably due to the contrasting sensitivity to chilling of their parents F. virginiana and F. chiloensis . The northern species, F. virginiana , has a longer chilling requirement than the southern species, F. chiloensis Generally for strawberries, it is known that as chilling time increases, flower induction also decreases. Thus Durner and Polling (1988) pointed out that chilling preceding the optimum digging date at the nursery was advantageous for early fruit production in warm regions, while extra chilling after the optimum digging date had a negative effect on flowering. However, exposure of plants to night temperatures of about 15°C and short photoperiods (conditioning for flowering treatment) resulted in higher early yield, at least for „Sweet Charlie‟ plug transplants in Florida (Bish et al ., 1996 ) and for „S. Sengana‟ in Germany (Reichart, 197 3). Plants exposed for two weeks to 15°C and 25°C during the dark and light periods, respectively, were more vigorous, and had improved stand establishment and capability to hold larger berries than plants grown at 35°C /25°C; however, there was no effect on flower induction. Lieten (1997) reported that chilled and University of Ghana http://ugspace.ug.edu.gh 16 non- chilled plants of „Elsanta‟ both produced flower trusses, but trusses of non -chilled plants were shorter. Additionally, early berry size was smaller and fruit quality was poorer in non-chilled versus chilled plants (Hamann and Poling, 1997) . University of Ghana http://ugspace.ug.edu.gh 17 CHAPTER THREE 3.0 MATERIALS AND METHODS 3.1 Plant mat erial and treat men ts used Six month old Japanese strawberry cultivars ( „Sachinoka ‟, „Tochiotome‟ and „Benihoppe‟) were used in this experiment in a completely randomized design. A completely randomized design was used. The treatments were set as control and shade. Three strawberry cultivars were used with eight (8) replications per cultivar. Two different sets of treatments were used. One set of treatment consisting of „Sachinoka ‟ , „Tochiotome „and „Benihoppe‟ were set as control and the same set of treatment were placed under shade in the screen house. The control had a total of twenty-four (24) plants and the shade treatment had a total of twenty-four (24) plants. The cultivars were propagated by runners in September, 2010 and were later transferred into plastic containers (14cm x 12 cm) containing a mixture of kanuma, vermiculite and peatmoss in the ratio 1:1:1 under plug fertigation system (N =7.2 : P=2.0: K=3.3: Ca=3.2: Mg=1.2: EC=1.0). The strawberry plants were treated with 150 mls of fertigated water five (5) times a day during the winter and later increased to seven (7 ) times a day in the summer because of high temperatures. The experiment was set up from March to August. Data collected during the period of the study included qualitative and qualitative parameters. The qualitative parameters included:  Fruit firmness  Fruit colour University of Ghana http://ugspace.ug.edu.gh 18  Titratable acidity  Total soluble solids  Percentage acidity  Sugar-acid ratio  pH Other plant parameters recorded included:  Number of fruits harvested  Fruit weight  Fruit length  Fruit width  Leaf area  Leaf length Environmental parameters were also recorded and these included:  Light intensity  Chlorophyll content  Temperature  Humidity University of Ghana http://ugspace.ug.edu.gh 19 Figure 1 : Contro l plants Figure 2 : Plants under shade tre a t me nt University of Ghana http://ugspace.ug.edu.gh 20 3.2 Mean fruit length, mean fruit weight, fruit wid th, petiole length (Leaf height), leaf wid th and leaf area The length (mm) of fruits was measured with a ruler from the tip of the fruit to the base of the pedicel. Fruit weight (kg) was measured using a weighing scale immediately after harvest. The diameter or width (mm) of fruits harvested was taken at the broadest part of the fruit with a venier caliper. Leaf height (cm), leaf area (cm²) and petiole length (cm) were all measured with a tape measure. 3.3 Relative Chlorophyll conten t An indirect index of chlorophyll content was measured with a leaf chlorophyll meter . Three SPAD measurements from locations between the veins were averaged to represent one observation. University of Ghana http://ugspace.ug.edu.gh 21 Figure 3 : Chloro phyll met er (Model SPAD-502, Minolta, Japa n) used for mea suring lea f chloro phyll during the experi me nta l per io d 3.4 Tempe rature, humidity and light inten sity Temperature and humidity were measured by use of data logger for the period of the experiment. Light intensity was measured at regular intervals with a photometer on a horizontal plane above the plant canopy. University of Ghana http://ugspace.ug.edu.gh 22 3.5 QUALITY MEASUREMENT 3.5.1 Fruit Firmn ess Fruit firmness was determined by using a universal testing machine (Fudoh Rheometer RT-3005D) and this was done immediately after harvesting. The machine was equipped with a load cell of 50 N for measuring the force that is required to push a cylindrical probe into the strawberries. The diameter of the plunger was 5 mm. The penetration depth was 5 mm and the speed at which the probe moved was 5 mm . These properties are most appropriate for measuring the firmness of small fruit such as strawberries (Hietaranta and Linna, 1999 ). Refer to figure 4 Figure 4 : Penet ro met er (Fudoh Rheomet er RT-3005D) used for mea suring fruit firmn es s during the study University of Ghana http://ugspace.ug.edu.gh 23 3.5.2 Colour measuremen t The surface color of each fruit was measured with a hand-held tristimulus reflectance colorimeter (Minolta, Model CR-300, Osaka, Japan ). Colour was recorded using the L*, a*, b* uniform colou r space (CIE Laboratories), where L * indicates lightness, a* indicates chromaticity on a green ( − ) to red (+) axis, and b* indicates chromaticity on a blue ( −) to yellow (+) axis. Numerical values of a * and b* were converted into hue angle ( Hue = b* /a * ) and chroma by the formula . (Refer to figure 5 ). Figure 5 : Calori met er (Minolta, Model CR-300, Osaka, Japa n) used for mea suring fruit colour during the study University of Ghana http://ugspace.ug.edu.gh 24 3.5.3 Preparation of samp les for chemical mea suremen t After firmness and color measurements, samples were kept in a refrigerator at -31ºC. Three fruits were chosen randomly from each month and chopped into small pieces with a knife. 1 g of sample was measured into 100ml/volume beaker and 4mls of distilled water was also added to the sample in the distilled water. The samples were then loaded into ependorf tubes and centrifuged at 13000rpm for 10 minutes (Figure 6 - figure 8 ). Figure 8: Centrifuge Figure 6: Fruit sa mple s fo r chemical ana ly sis Figure 7: Ground fruit sa mp les University of Ghana http://ugspace.ug.edu.gh 25 3.5.4 Soluble soli d s (SSC), pH and Titratab le acids (TA) The soluble solid content (SSC) of the juice samples was determined with a hand held refractometer and was expressed in terms of percentage. The pH of the juice samples was determined using a pH meter that had previously been standardized to pH 4 and 7. For total titratable acidity (TTA) measurement, aliquots (6.00 g) of juice were diluted with 5ml of distilled water and the titratable acidity determined by titration with 0 .1molL −1 NaOH to an end point (that is when a pink colour was obtained). The results were converted to percentage acidity by the formula (Titre value * acid factor *1.0283*0.25* 100) /1 ml juice Figure 10: Refractomet er (Palet t e 100 PR-100, AT AGO- Spectrum Technolog ies,Plainfield,IL) used for mea suring brix during the experi me nta l per io d Figure 9: pH meter (pH - 526; WTW measure ment sy st e ms, Wisse nschaftlich - Technische Werkst a t t en GmbH, Wellhel m, Ger ma ny) University of Ghana http://ugspace.ug.edu.gh 26 3.6 STATISTICAL ANALYSIS The Statistical Analysis System computer package was used for the analysis. Data were analyzed by analysis of variance (ANOVA) and significant differences were detected by Tukey- Kramer test at P < 0.05. University of Ghana http://ugspace.ug.edu.gh 27 CHAPTER FOUR 4.0 RESULTS 4.1 TOTAL NUMBER OF FRUITS HARVESTED DURING THE STUDY Table 1 : Total number of fruits harvested MONTH CULTIVAR MAY JUNE JULY A(CONTROL) SACHINOKA 7 27 6 TOCHIOTOME 13 17 13 BENIHOPP E 11 14 14 B (SHADED) SACHINOKA 15 16 2 TOCHIOTOME 22 7 11 BENIHOPP E 24 7 3 Total number of fruits (yield) harvested (Table 1) were different for all the cultivars. „Tochiotome‟ recorded the highest number of fruits for the control plants followed by „Sachinoka ‟ and „Benihoppe‟. For the shaded cultivars, „Tochiotome‟ had the highest number of fruits followed by „Benihoppe‟ and „Sachinoka ‟. University of Ghana http://ugspace.ug.edu.gh 28 4.2 Fruit weight Table 2 : Effect of shade on mean fruit weight (g ) of the three (3) straw b erry cultivars MONTHS CULTIVAR MAY JUNE JULY MEAN A (CONTROL) SACHINOKA 10.5 0 12.89 9.75 11.05 TOCHIOTOME 16. 4 0 12.69 12.37 13.82 BENIHOPP E 17.7 0 16.52 9.79 14.67 NS NS NS LSD ( 0.05) 0.12 0 0.05 0 0.46 0 B ( SHADED) SACHINOKA 15.1 0 11.04 9.2 0 11.78 TOCHIOTOME 18.09 12.6 0 10 .00 13.56 BENIHOPP E 16.93 12.2 0 7.2 0 12.11 NS NS NS LSD ( 0.05) 0.482 0.809 0.638 For the control, the average weight/ plant (Table 2 ) showed no significant difference among the three cultivars. However, the highest mean weight was recorded for „Benihoppe‟ (14.67g/plant) which is known to be a high yielding cultivar and the lowest was recorded for Sachinoka (11.05g/plant). With the shaded treatment (Table 2 ), mean fruit weight decreased from May to July . However there were no significant differences observed. The highest mean fruit weight University of Ghana http://ugspace.ug.edu.gh 29 was recorded in „Tohiotome‟ (13.56g/plant) and the lowest for „Sachinoka ‟ (11.78g/plant). 4.3 Fruit length Table 3 : Effect of shade on mean fruit length (mm) of the three straw b erry cultivars MONTHS CULTIVAR A (CONTROL) MAY JUNE JULY MEAN SACHINOKA 32.30 a 34.31 a 30.68 32.4 3 TOCHIOTOME 38.60 a 33.55 a 31.21 51.68 BENIHOPP E 42.90 a 39.89 a 29.89 37.56 NS LSD ( 0.05) 0.014 0.014 0.765 B ( SHADED) SACHINOKA 35.23 29.20 33.35 32.59 TOCHIOTOME 39.52 33.10 32.16 34.93 BENIHOPP E 38.55 34.70 26.80 33.35 NS NS NS LSD ( 0.05) 0.17 0 0.112 0.098 Means followed by the same letter are not significantly different Fruit length (mm) decreased steadily from May to July in both treatments. There were no significant differences among the unshaded plants. The highest mean fruit length was University of Ghana http://ugspace.ug.edu.gh 30 recorded from „Tochiotome‟ (34.93mm) and the lowest was recorded from „Sachinoka ‟ (32.59mm). The shade plants showed significant differences in fruit length. In May after separation by Turkeys, the differences were not significant. The trend was similar in June. However, in July no significant differences were recorded among the cultivars. However, the highest mean fruit length was recorded from Tochiotome (51.67mm) and the lowest for Sachinoka (32.43mm). University of Ghana http://ugspace.ug.edu.gh 31 4.4 Fruit wid th Table 4 : Effect of shade on mean fruit wid th (cm) of the straw b erry cultivars MONTHS CULTIVAR A (CONTROL) MAY JUNE JULY MEAN SACHINOKA 27.47 28.93 26.52 27.64 TOCHIOTOME 31.89 32.19 28.23 30.77 BENIHOPP E 32.34 28.95 26.59 29.29 NS NS NS LSD ( 0.05) 0.134 0.087 0.572 B(SHADED) SACHINOKA 31.17 27.44 27.7 0 28.77 TOCHIOTOME 32.21 29.53 26.48 29.41 BENIHOPP E 30.15 27.59 23.43 27.06 NS NS NS LSD ( 0.05) 0.390 0.649 0.382 Fruit width for unshaded plants (Table 4 ) increased steadily from May to July . Tochiotome recorded the highest mean fruit width (30.77) and the lowest for „Sachinoka ‟ (27.64). The differences which occurred were not significant. With the shaded plants, „Tochiotome‟ recorded the highest mean fruit width (29.41 ) and the lowest mean fruit University of Ghana http://ugspace.ug.edu.gh 32 width was recorded by „Benihoppe‟ (27.06). However, there were no significant differences in the values obtained. 4.5 Leaf height Table 5 : Effect of shade the mean leaf height (cm) of the three straw b erry cultiva rs MONTHS CULTIVAR MAY JUNE JULY MEAN A (CONTROL) SACHINOKA 20.56 b 26.36 27.25 24.72 TOCHIOTOME 19.12b c 27.84 29.44 25.47 BENIHOPP E 28.06 a 28.19 29.62 28.62 NS NS LSD ( 0.05) 0.001 0.498 0.28 0 B ( SHADED) SACHINOKA 19.57 bc 26 .00 25.81bc 23.79 TOCHIOTOME 21.75b 27.74 28.25b 25.91 BENIHOPP E 30.56a 30.46 34.08a 31.7 0 NS LSD ( 0.05) 0.001 0.088 0.001 Means followed by the same letter are not significantly different Table 5 shows the leaf area measurement for the three strawberry cultivars used in the study. Leaf height increased from May to July with increase in temperature. With the University of Ghana http://ugspace.ug.edu.gh 33 unshaded plants, significant differences were observed in May. However, no significant differences were observed in June and July. „Benihoppe‟ recorded the highest mean leaf height (28.62cm) and the lowest for „Sachinoka‟ (24.72cm ). With the shaded cultivars, May and July recorded significant differences in the mean leaf area values obtained. However, „Benihoppe‟ recorded the highest mean leaf height (31.70cm) and the lowest mean leaf height for „Sachinoka ‟ (23.79cm). 4.6 Leaf area Table 6 : Effect of shade on the mean leaf area (cm²) of the three straw b erry cultivars MONTHS CULTIVAR MAY JUNE JULY MEAN A (CONTROL) SACHIN OKA 54.40 b 57.80c 52.40 c 54.87 TOCHIOTOME 190.90 a 114.6 a 111.6 a 139.03 BENIHOPP E 97.50 a 84.20 b 76.60 b 129.15 LSD ( 0.05) 0.006 0.001 0.001 B ( SHADED) SACHINOKA 80.30 c 67.80 a 76.80 112.45 TOCHIOTOME 109.10 b 104.9 a 92.60 102.2 BENIHOPP E 136.40a 87.90 a 89.60 104.63 NS LSD ( 0.05) 0.001 0.012 0.345 University of Ghana http://ugspace.ug.edu.gh 34 Means followed by the same letter are not significantly different Leaf area (cm² ) decreased steadily from May to July for both the control and shade plants. However with the contro l, significant differences were observed from May to July. However, Tochiotome recorded the highest mean leaf area (139.0 3 cm²) and the lowest leaf area was recorded from Sachinoka (54. 87 cm²). The shaded plants also showed a decline in leaf area from May to July. There were significant differences in the strawberry cultivars. However, the highest mean leaf area was recorded from Benihoppe (104.63 cm²) and the lowest leaf area was also recorded from Tochiotome (102.2 0 cm²). University of Ghana http://ugspace.ug.edu.gh 35 4.7 Chlorophyll conten t Table 7 : Variation in Chlorophyll conten t of the three straw b erry culti vars MONTHS CULTIVAR MAY JUNE JULY MEAN A (CONTROL) SACHINOKA 38.40 40.10 42.80 40.43 TOCHIOTOME 39.08 41.20 49.90 43.39 BENIHOPP E 37.59 35.80 44.10 39.16 NS NS NS LSD ( 0.05) 0.769 0.279 0.079 B (SHADED) SACHINOKA 39.26 40.60 45.00 42.80 TOCHIOTOME 43.64 42.10 45.70 43.90 BENIHOPP E 38.51 38.00 34.60 36.30 NS NS NS LSD ( 0.05) 0.026 0.292 0.178 * Means follow ed by the same letter are not significantly different Relative chlorophyll content (Table 7) increased steadily from May to July for the control plants with Tochiotome recording the highest chlorophyll content followed by Sachinoka and then Benihoppe. However, the differences that occurred were not significant. Relative chlorophyll content also showed an increased trend for the shaded plants from May to July with Tochiotome recording the highest chlorophyll content followed by University of Ghana http://ugspace.ug.edu.gh 36 Sachinoka and then Benihoppe. In May significant differences was observed among the cultivars but the differences were not statistically significant. 4.8 Light inten sity Light intensity( BRIGHT DAY) 0.00 200.00 400.00 600.00 800.00 1000.00 1200.00 1400.00 8 a.m 10 a.m 12 p. m 2 p.m 4 p.m Time( hrs) A m o u n t o f l i g h t shade control Figure 11: Light inte nsit y varia t io n mea sure d during bri ght day s at two hour interv al Light intensity( cloudy day) 0.00 200.00 400.00 600.00 800.00 10 . 12 8 a.m 10 a.m 12 p. m 2 p.m 4 p.m Time( hrs) A m o u n t o f l i g h t shade control Figure 12: Light inte nsit y varia t io n mea sure d on sunny day s at two hour interv a l University of Ghana http://ugspace.ug.edu.gh 37 Light intensity measured with a photometer on both sunny and bright day‟s showed similar trends. It was observed that the amount of light received by the strawberry cultivars was very low in the mornings. The highest light intensity was always recorded around mid-day and then declined steadily towards the evening. 4.9 Tempe rature The highest temperature occurred in July with an average temperature of about 25ºC. Maximum average temperature was 34 ºC and minimum average was around 22 ºC. In June, average temperature was around 24 ºC with maximum and minimum averages of 31 ºC and 17 ºC respectively. The month May had the lowest average temperature of 20 ºC with maximum and minimum average temperatures at 14 ºC and 26 ºC, respectively. Temperature 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 MAY JUNE JULY T e m p e r a t u r e ( C ) control shade Figure 13: Tempera ture varia t io n mea sure ment s during the experi me nta l per io d University of Ghana http://ugspace.ug.edu.gh 38 4.10 Humidity The highest average humidity occurred in June (78 %) which was followed by May (71%) and then July recorded the least humidity of 70%. Humidity 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 MAY JUNE JULY H u m i d i t y ( % ) control shade Figure 14: Humidit y mea sure me nt duri ng the experi men t a l per io d University of Ghana http://ugspace.ug.edu.gh 39 4.11 QUALITY ANALYSIS 4.11.1 Fruit fir mn ess Table 8 : Effect of shade on the mean fruit firmn ess (kg /N ) of the straw b erry cultivars FRUIT FIRMNESS (Kg/N) MONTHS CULTIVAR MAY JUNE JULY MEAN A(CONTROL) SACHINOKA 0.0459 0.0426 0.0379a 0.1264 TOCHIOTOME 0.048 0.0407 0.0282a 0.0389 BENIHOPP E 0.0 62 0.0427 0.0270a 0.0439 NS NS LSD ( 0.05) 0.567 0.9 00 0.016 B ( SHADED) SACHINOKA 0.0457 0.044 0.0404 0.04337 TOCHIOTOME 0.0478 0.037 0.0372 0.04067 BENIHOPP E 0.0384 0.0527 0.0440 0.04503 NS NS NS LSD ( 0.05) 0.299 0.474 0.513 Means follow ed by the same letter are not significantly different Fruit firmness analysis (Table 8) showed no significant differences among the three strawberry cultivars used in this study in May and June for the control plants. However, University of Ghana http://ugspace.ug.edu.gh 40 differences were observed in July among the cultivars but these were not statistically significant at P<0.05. 4.11.2 Fruit colour Table 9: Fruit colour measuremen t of the stra w b erry cultivars used in the study FRUIT COLOUR MONTH CULTIVAR MAY JUNE JULY A(CONTROL) L Hue Chroma L Hue Chroma L Hue Chroma Sachinoka 41. 31 35. 18 18. 27 37. 38 29. 94 16. 17 32. 29 26. 96 21. 35 38. 21 33. 71 14. 13 40. 33 38. 88 23. 43 33. 94 26. 98 29. 40 Tochiotome 39. 44 37. 49 52. 19 34. 88 32. 40 16. 95 13. 86 45. 50 43. 95 40. 19 33. 88 39. 55 39. 36 33. 81 71. 39 16. 20 40. 49 94. 84 Beni op pe 30. 46 30. 12 19. 58 18. 28 42. 85 32. 78 39. 50 38. 61 65. 51 40. 19 33. 88 18. 25 38. 38 38. 16 54. 15 39. 50 37. 33 93. 03 B(SHADE) Sachinoka 30. 00 27. 00 16. 30 27. 30 19. 90 20. 20 20. 20 12. 00 28. 00 Tochiotome 29. 20 16. 50 17. 60 26. 40 15. 10 21. 70 20. 80 12. 50 25. 60 Benihoppe 24. 00 12. 00 25. 50 22. 50 13. 00 25. 50 36. 80 14. 90 38. 70 Table 9 shows the colour of fruits of the three strawberry cultivars used in the study. L indicates lightness, hue indicates chromaticity on a green (−) to red (+) axis, and chroma indicates chromaticity on a blue (−) to yellow (+) axis . University of Ghana http://ugspace.ug.edu.gh 41 4.11.3 Soluble soli d conten t Table 10 : Effect of shade on the total Soluble Solid Conten t (% ) of the three straw b erry cultivars Soluble Solid Conten t (%) MONTHS CULTIVAR MAY JUNE JULY MEAN A(CONTROL) Sachinoka 8.40 9.00 9.20 8.87 Tochiotome 4.80 7.00 8.40 6.73 Benihoppe 11.20 8.60 9.20 9.67 B(SHADED) Sachinoka 6.00 4.60 6.40 5.67 Tochiotome 14.40 8.00 7.20 9.87 Benihoppe 7.20 9.20 8.00 8.13 Soluble solid content (Table 10 ) increased in some of the cultivars towards July due to high temperature. Among the unshaded plants, Benihoppe recorded the highest mean soluble content, which was followed by Sachinoka and Tochiotome. The shaded cultivars also showed differences in soluble solid content. All the three varieties showed a decline in soluble solid content from May to July with Tochiotome recording the highest soluble content followed by Benihoppe and then Sachinoka. University of Ghana http://ugspace.ug.edu.gh 42 4.11.4 Titratab le acidity Table 1 1: Effect of shade on titratab le acidity (mls) of the straw b erry cultivars Titratab le Acidity (mls) MONTHS CULTIVAR MAY JUNE JULY MEAN A(CONTROL) Sachinoka 2.95 4.13 3.65 3.58 Tochiotome 3.00 3.18 3.93 3.37 Benihoppe 5.70 3.55 3.45 4.23 B(SHADED) Sachinoka 2.75 3.28 3.50 3.18 Tochiotome 4.00 2.90 3.88 3.59 Benihoppe 2.60 3.05 3.40 3.02 Acidity (Table 11) measurement for the unshaded cultivars showed that Benihoppe recorded the highest mean acidity followed by Sachinoka and then Tochiotome. With the shaded plants, Tochiotome recorded the highest acidity followed by Sachinoka and then Benihoppe. University of Ghana http://ugspace.ug.edu.gh 43 4.11.5 Sugar:acid ratio Table 1 2: Effect of shade on Sugar:acid ratio of the three cultivars Sugar:Acid ratio MONTHS CULTIVAR MAY JUNE JULY MEAN A(CONTROL) Sachinoka 2.84 2.18 2.52 2.51 Tochiotome 1.60 2.20 2.14 1.98 Benihoppe 1.96 2.42 2.67 2.35 B(SHADE) Sachinoka 2.18 1.40 1.83 1.80 Tochiotome 3.60 2.76 1.86 2.74 Benihoppe 2.77 3.02 2.35 2.71 Sugar -acid ratio (Table 12) varied among the cultivars used in the study. For the unshaded plants, Sachinoka recorded the highest mean soluble content which was followed by Benihoppe and then Tochiotome. Under shade, Benihoppe recorded the highest mean soluble content followed by Tochiotome and Sachinoka. University of Ghana http://ugspace.ug.edu.gh 44 4.11.6 Percentage acidity Table 1 3: Effect of shade on the Percentage (% ) acid conten t of the three straw b erry cultivars Acid Conten t (%) MONTHS CULTIVAR MAY JUNE JULY MEAN A(CONTROL) Sachinoka 0.4854 0.6795 0.6005 0.5885 Tochiotome 0.4936 0.5232 0.6466 0.5545 Benihoppe 0.9378 0.5841 0.5676 0.6965 B(SHADED) Sachinoka 0.4525 0.5397 0.5758 0.5227 Tochiotome 0.6581 0.4771 0.6384 0.5912 Benihoppe 0.4278 0.5018 0.5594 0.4963 Percentage acidity of fruits reduced in all the treatments both control and shade (Table 13). For the unshaded plants, Benihoppe recorded the highest mean percentage acid for the control cultivars followed by Sachinoka and Tochiotome. When plants were shaded, fruits of Tochiotome recorded the highest percentage acid followed by Sachinoka and then Benihoppe. University of Ghana http://ugspace.ug.edu.gh 45 4.11.7 pH Table 1 4 : Effect of shade on pH of the straw b erry cultivars used Fruit pH MONTHS CULTIVAR MAY JUNE JULY MEAN A(CONTROL) Sachinoka 3.70 3.70 3.70 3.70 Tochiotome 4.00 3.70 3.70 3.80 Benihoppe 3.70 3.70 3.50 3.63 B(SHADED) Sachinoka 3.70 3.70 3.50 3.63 Tochiotome 3.70 3.70 3.50 3.63 Benihoppe 3.80 3.70 3.70 3.73 pH values did not show much differences among the cultivars used in the study.With the unshaded plants, Tochiotome recorded the highest mean pH (3.80) followed by Sachinoka (3.70 ) and then Benihoppe (3.63 ). With the shaded plants, Benihoppe recorded the highest mean pH (3.7 3) but Sachinoka and Tochiotome had the same mean pH values (3.70). University of Ghana http://ugspace.ug.edu.gh 46 CHAPTER FIVE 5.0 DISCUSSION 5.1 Effect of temp erature on tota l number of fruits / plan t The number of strawberry flowers and fruits are related to number and diameter of crowns, which can be used to predict plant yield potential (Hancock, 1999 ). Himelrick et al. (1990 ) reported that genetic and environmental variations are not the only factors that affect strawberry fruit production. Temperature and climatic factors like humidity could also influence strawberry fruit production. Temperature increased steadily throughout the study period. Temperature range for this study was between 20 to 34 ºC . In this study, while temperature increased from May to July, fruit numbers reduced significantly. With the unshaded plants, Sachinoka recorded the highest fruit number (27.0 0 ) followed by Tochiotome (17.00) and then Benihoppe (14.00) which occurred in June with maximum and minimum temperature of 31/17 ºC. However, the average temperature recorded in June was 2 4 ºC. With the shaded plants, Tochiotome recorded the highest number of fruits (22.00) and this occurred in May with maximum and minimum temperature of 2 6/14 ºC. However, average temperature recorded in May was 20 ºC. Burke (1990 ) observed that as maximum and minimum average temperatures increased , plant growth decreased which may have been due to the tendency for high temperature to enhance dark respiration, inhibit cellular metabolism and chloroplast biogenesis, reduce chloroplast photoreductive activity, and cause disruption of protein lipid interactions and decreased photosynthetic capacity. Hellman and Travis (1988) also showed that higher temperatures (35-40 º C) inhibit ed growth of June bearing strawberries. The least number University of Ghana http://ugspace.ug.edu.gh 47 of fruits were produced in July which had the maximum and minimum temperature of 34/23 º C and average temperature of 26 º C. This study also revealed similar results. A t higher growth temperatures of 34/23 º C which occurred in July, Benihoppe recorded a total of 14 fruits followed by Tochiotome with 13 fruits and Sachinoka with only 6 fruits for the control. With the shaded plants where temperature wa s higher, „Tochiotome‟ recorded 11 fruits which were followed by „Benihoppe‟ with 6 fruits and then „Sachinoka ‟ with 6 fruits. 5.2 Effect of temp erature on fresh fruit weight, fruit length and fruit width Fresh fruit weight, fruit width and fruit length are important factors in strawberry quality, which depend on water content in plant (Saied et al ., 2005). In addition, there are direct correlation between sugar concentration and nitrogen content of fruits (Lasertosa et al ., 1999). In this study, fresh fruit weight, fruit length and fruit width decreased as temperature increased from May to July. Fresh fruit weight measured during the study did not show any significant differences in both the control and the shaded plants. However, the heaviest fruit weight for the control was recorded from Benihoppe (17.70g) in May with maximum and minimum temperature of 2 6/14 ºC and the lightest fruit weight was recorded for Sachinoka (9.75g) in July. For the shaded plants, the heaviest fruit weight was recorded from Tochiotome (18.0 9g) in May and the lightest fruit weight was recorded from Benihoppe (7.20g). Mori (1998) showed that yield and fresh fruit weight of strawberry were negatively affected by increase in temperature which was very evident in this experiment University of Ghana http://ugspace.ug.edu.gh 48 Fruit length measured for the control plants showed no significant difference. However, the longest fruit length was recorded from Tochiotome (39.52mm) which occurred in May and the smallest fruit length was recorded from Benihoppe (26.80mm) in July. For the shade plants, significant differences were observed in May and June. However, the differences were not significant after separation. Benihoppe recorded both the longest and smallest fruit lengths. In May, Benihoppe recorded the longest fruit length (42.90mm) and also recorded the smallest fruit length (29.89mm) in July. Fruit width did not show any significant differences among the cultivars. However for the control, Benihoppe recorded both the longest and smallest fruit widths. The longest width (32.34mm) was recorded in May and the smallest fruit width (26.59mm) was also recorded in July. For the shaded plants, Tochiotome recorded the longest fruit width (32.21mm) whereas Benihoppe recorded the smallest fruit width (23.43mm). 5.3 Effect of temp erature on l eaf area and leaf height of strawberry cultivars used in the study The ability of the plant to photosynthesize leading to subsequent fruit production depends largely on the leaf area. The leaf surface serves as a point of interception of light and entry point of chlorophyll which are both important inputs for the growth and development of all plants. However, strawberry plants grown at higher temperatures have smaller leaf size and leaf area (Wang et al., 2000). Le Mière et al. (1998) also found that the canopy development in strawberry was more limited at warmer temperatures leading to lower rate of photosynthesis and subsequent lower fruit yield. Plants exposed University of Ghana http://ugspace.ug.edu.gh 49 to higher temperature regimes appear to develop faster vegetatively as compared to reproductive growth (Wahid et al ., 2007). In this study, leaf area also decreased as temperature increased, while petiole length increased. Jiao et al. (199 8) reported that carbohydrate export rate of expanded leaves on the flowering shoot was reduced by 80% under high temperature (40°C) and suggested that temperature influences export and partitioning of assimilates. The unshaded plants recorded relatively smaller leaf areas and higher petiole lengths as compared to the shaded plants. Therefore at higher temperatures, more assimilates are directed towards the development of shoots as compared to fruit development (fruit weight, fruit width and fruit length). For this reason, leaf sizes and for that matter leaf area were compromised leading to increasing shoot system which was evident in this study. 5.4 Light inten sity Sunlight is not the only source of energy for photosynthesis, but also the most important factor affecting productivity in horticultural crops (Papadopoulos and Pararajasingham, 1997; Gregoriu et al ., 2007). Carbon exchange rate (CER) is strongly dependent on irradiance, absorption, and utilization of photon energy (Gregoriu et al ., 2007). Low irradiance, in as much as it determines insufficient light penetration into the canopy, influences CER directly by reducing photon energy utilization, thus decreasing productivity (Hampson et al . , 1996 ). Light intensity measurement in this study increased from the mornings to about 12 mid-day and then declined towards the evenings. Light intensity for both the unshaded and shaded cultivars recorded the same pattern. Relatively, the amount of light intensities received on bright and cloudy days was higher University of Ghana http://ugspace.ug.edu.gh 50 for the shaded plants than the unshaded plants. This is because the shade material might have absorbed heat leading to the increase in temperature around fruits under the shade which negatively affected fruit production. At high light intensities, the rate of transpiration and chlorophyll uptake by leaves of plants tend to be higher. This is particularly important for horticultural crops like strawberry which are mostly cultivated in the temperate zones. 5.5 Chlorophyll Gulen et al. (2003 ) suggested that longer exposure of strawberry plants to temperature increased chlorophyll content. It is known that at higher temperatures, the amount of chlorophyll also increases. Chlorophyll content is usually higher when the rate of transpiration is high and plant leaves are fully exposed. In this study there was an increase of chlorophyll content with increasing temperatures which was in agreement with an increase in chlorophyll content of grapevines grown in controlled environment (Fukuda et al., 1988) and in mulberry ( Morus Spp.L.) plants exposed to high temperature. In this study, there were no significant differences in the leaf chlorophyll of the control plants. Tochiotome recorded the highest chlorophyll content (49.90) in July and the lowest chlorophyll content (35.80) was recorded by Benihoppe in June. For the shade plants, significant differences were observed in May. Upon separation, the differences were not significant. However, the highest chlorophyll (45.70) content was recorded from Tochiotome in July and the lowest chlorophyll (38.00) content was recorded from Benihoppe in June. Gulen et al., (2003 ) concluded that variations in the amount of University of Ghana http://ugspace.ug.edu.gh 51 chlorophyll synthesised by plants could be attributed to the length of exposure and difference in plant species, prominence and source of stress (Dekov et al., 2000) or an increase in leaf thickness which leads to concentration of higher chlorophyll content (Abdelrahman, 1984). 5.6 Fruit fir mn ess Strawberries show a continuous decrease of cell wall content during ripening (Perkins- Veazie, 1995; Rosli et al. , 2004). Moreover, there are multiple chemical changes that involve pectins and the cellulose-xyloglucan framework resulting in solubilization of polyuronides and hemicelluloses (Knee et al. , 19 77) and loss of neutral sugars (Rosli et al. , 2004). Huber (1984) stated that strawberry softening may be caused by the action of several enzymes, and may be accompanied by a loss of calcium. At higher temperatures, softening of strawberry fruit, either during ripening in the field or during storage is paramount and this is mainly due to loss of cell wall material, which is more pronounced in the cortical tissue (Koh and Melton, 2004). This study revealed that overall fruit firmness of strawberry fruits reduced as temperature increased from May to July . For the unshaded plants, significant differences were observed in July. However, differences were not statistically significant. The highest fruit firmness (0.0620 kg) was recorded from Benihoppe in May and the lowest fruit firmness (0.0282 kg) was recorded for Tochiotome in July. For the shaded plants, where temperatures were higher, Tochiotome recorded both the highest and lowest fruit firmness. The highest fruit University of Ghana http://ugspace.ug.edu.gh 52 firmness (0.0478kg) was recorded in May and the lowest (0.0370kg) was also recorded in June. However, there were no significant differences observed. Texture changes were more evident in the shaded plants than the un shaded plants. Soft texture would shorten the shelf- life since it will become prone to mechanical injury and mould contamination. The better firmness values recorded for the unshaded plants make them most suitable for cold storage and also handling since they are more resistant to physical injuries and abrasions. 5.7 Fruit colour Among the different physical quality parameters of fruits, fruit colou r is a special character which appeals the customer and is also one of the important maturity indices of fruits and vegetables. In the case of strawberries, two anthocyanidin glycosides, pelargonidin 3-glucoside and cyanidin 3-glucoside, are almost exclusively responsible for the red color of strawberries (Kalt et al . , 1993; Gil et al ., 1997 ). The loss of a good characteristic colour in strawberries has been attributed to many factors including maturity, genotype or cultivar, methods of harvesting and handling, cultural practices, and environmental factors (Sistrunk and Morris, 1985). Many researches including Furney et al., (1998 ) indicate d that higher temperatures results in development of red colour in strawberry fruits. Similar observations were made in this study. In this study, when the day/ night temperature increased, the L*(Luminance) value and hue angle generally decreased while the chroma value generally increased. These indicated that as the day or night temperature became warmer, the fruit surface colour in University of Ghana http://ugspace.ug.edu.gh 53 both the control and shaded plants became darker (L*value decreased), redder (hue angle decreased), and greater in pigment intensity (chroma value increased) for the three cultivars. 5.8 Total soluble solid s (TSS) and sugar: acid ratio Soluble sugar content and sugar:acid ratio acidity may vary depending on the cultivar. Shaw (1990) showed that soluble solids content was more dependent on environmental conditions than genetic inheritance, while Kader (1991) found that fruit from summer- planted strawberries were higher in soluble solids and titratable acidity than those of winter-planted fruit. The results showed that changes in TSS during storage time vigorously depend on cultivar. The total soluble solid of mature strawberries has been reported to decrease under cold storage as a result of respiration (Garcia et al. , 1998). When the plants were not shaded, Sachinoka recorded the highest sugar content (9.20) in July and the lowest sugar content (4.40) was recorded for Tochiotome in May. With the shaded plants, Tochiotme recorded the highest soluble sugar content (14.4 0) in May and the lowest sugar content (6.00) was recorded from Sachinoka in May. Hellman and Travis (1988) found that when high temperature treatments (25/15, 30/20, 35/25, and 40/30 ºC day/night temperature) were imposed on plants with approximately 50% of primary fruits just beginning to colour, soluble solid content of the fruit showed a significant negative relationship with temperature within the range of 25-40 ºC. Sucrose is the primary source of glucose and fructose therefore, the increased amount of these monossacharides could account for the decrease in sucrose level. However, the TSS increase indicates that sucrose synthesis had taken place during cold-storage. University of Ghana http://ugspace.ug.edu.gh 54 5.9 Titratab le acidity, percentage acidity and pH Shaw (1990) concluded that titratable acidity and for that matter percentage acidity was a heritable trait, less influenced by environment than soluble solids content. However, application of nitrogen fertilizer or pre-harvest shading of strawberry fruit could decrease titratable acidity (Saxena and Locascio, 1968; Osman and Dodd, 1992). In this study, titratable acidity measurements also varied depending on the cultivar. For the unshaded plants, Benihoppe recorded the highest mean acidity (4.23mls) followed by Tochiotome (3.37mls). For the shaded cultivars, Tochiotome recorded the highest mean acidity (3.59mls) followed by Sachinoka (3.18mls) and then Benihoppe (3.02mls). Percentage acidity increased throughout the study period. For the control plants, Benihoppee recorded the highest mean percentage acidity (0.6965 ) which was followed by Sachinoka (0.5885 ) and then Tochiotme (0.5545). The shaded cultivars also recorded the highest mean percentage acidity in Tochiotome (0.5912) which was followed by Sachinoka (0.5227) and then Benihoppe (0.4963). Organic, non-volatile acids are the second most important component of strawberry flavour, after soluble sugars. The main compound accounting for titratable acid (TA) is citric acid, which is predominant (over 90%) in strawberry. These acids regulate the cellular pH and may influence the anthocyanin stability and, as a consequence, the colour of the fruit. However, there is little published information about changes of pH and TA content in strawberry fruit grown under high temperatures. University of Ghana http://ugspace.ug.edu.gh 55 pH of both shaded and unshaded plants ranged between 3.50 and 4.00, values that are above the average for ripe strawberry, pH of 3.30 ( Green, 1971) . With the unshaded plants, Tochiotome recorded the highest mean pH (3.80) which was followed by Sachinoka (3.70) and then Benihoppe (3.62). However, Benihoppe recorded the highest mean pH (3.73) in the shaded cultivars which was followed by Tochiotome (3.63) and then Sachinoka (3.63). University of Ghana http://ugspace.ug.edu.gh 56 CHAPTER SIX 6.0 CONCLUSION AND RECOMMENDATIONS 6.1 CONCLUSI ON This study revealed that increase in temperature greatly reduced the total number of fruits harvested. The least number of fruits were produced in July with maximum and minimum temperature of 34/23 º C. Maximum fruit numbers were recorded by three cultivars used in the study in May with maximum and minimum temperatures of 26/14 ºC. Therefore, this study revealed that the optimum temperatures for maximum development of strawberry fruits are 26 /1 4 ºC. Fresh fruit weight, fruit length and fruit width reduced as temperature increased throughout the study. Inspite of increasing temperatures, Benihoppe produced bigger fruits at higher temperatures. Sachinoka on the other hand, at higher temperatures, produced smaller fruits. However, under shade, Tochiotome produced appreciable fruit weight. Benihoppe produced the least fruit weight under shade. Tochiotome produced longer fruit length even under high temperatures whereas Benihoppe produced smaller fruit length under high temperatures when grown without shade. However, Benihoppe produced longer and wider fruits under shade treatment. Increasing temperatures from May to July greatly reduced leaf area. On the contrary, leaf height increased with increasing temperatures. Tochiotome produced larger leaf area in University of Ghana http://ugspace.ug.edu.gh 57 this study. Increased in temperature greatly reduced the leaf area of Sachinoka. Benihoppe showed an increased in leaf height as growth temperatures increased from May to July. As temperature increased, the chlorophyll content also increased considerably. At higher temperatures, Tochiotome produced relatively higher chlorophyll content in leaves. However, Benhihoppe produced low levels of chlorophyll in plant leaves which subsequently led to lower fruit production. Increase in growth temperatures greatly reduced the firmness of the strawberry fruits used in this study. At high temperatures, Benihoppe produced firmer fruits for the control plants. However under shade treatment, Tochiotome produced relatively firm fruits than the other cultivars. Higher temperatures induced darker fruit colour in all the three cultivars used in this study. As temperature increased, chemical composition of fruits also varied among the cultivars used in this study. Higher temperatures increased soluble solid content of cultivars used in the study. Sugar-acid ratio and acidity measurements also varied depending on the cultivar. pH values declined as temperature increased from May to July. University of Ghana http://ugspace.ug.edu.gh 58 6.2 RECOMMENDATIONS 1. Further studies should be carried out in the open field under high temperatures for further analysis of yield and quality parameters of the three strawberry cultivars used in this study. 2. Similar experiment should also be carried out to confirm the results of this study. 3. Tochiotome and Benihoppe cultivars appear to be high yielding under high temperature and therefore further studies on these two cultivars should be done under tropical conditions to also determine the level of productivity and quality. 4. Similar expe riments should be carried out using different growth media to observe the growth characteristics of the cultivars used in this study. University of Ghana http://ugspace.ug.edu.gh 59 REFERENCES Adams, S.R., K.E Cockshull and C.R.J Cave. (2001 ). Effect of temperature on the growth and development of tomato fruits. Annu. Bot. 88: 869 -877. Abdelrahman, M.H. (198 4 ). Growth and productivity of strawberry cultivars at high temperatures. PhD thesis, Kans. State Univ., Manhattan. Almeida, A.A.F. and R.R. Valle. (2007 ). Ecophysiology of cacao tree. Braz. J. Plant Physiol. 19(4), 425 -448. Avigdori-Avidov, H. (19 86 ). Strawberry. In: Monselise, S.P. 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Effect of temperature and its shift on growth and anthocyanin production in suspension cultures of strawberry cells. Plant Sci. 127: 207-214. University of Ghana http://ugspace.ug.edu.gh 70 APPENDIX ANOVA USED FOR ANALYSIS CHLOROPHYLL CONTENT Chlorophyll content for May Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 8.88 4.44 0.27 0.769 Residual 21 350.84 16.71 Total 23 359.72 Chlorophyll content for June Source of variation d.f. s.s. m.s. v.r. F pr. Variety 2 129.22 64.61 1.36 0.279 Residual 21 1000.12 47.62 Total 23 1129.34 Variate: Chlorophyll content July Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 230.03 115.02 2.87 0.079 Residual 21 840.12 40.01 Total 23 1070.15 University of Ghana http://ugspace.ug.edu.gh 71 Shade Chlorophyll content for M ay Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 122.58 61.29 4.34 0.026 Residual 21 296.65 14.13 Total 23 419.23 Variate:Chlorophyll content june Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 69.61 34.81 1.31 0.292 Residual 21 559.60 26.65 Total 23 629 .21 Variate:Chlorophyll content July Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 627.6 313.8 1.88 0.178 Residual 21 3512.3 167.3 Total 23 4139.9 University of Ghana http://ugspace.ug.edu.gh 72 Fruit wid th Control Variate: Fruit width May Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 111.61 55.81 2.18 0.134 Residual 25 639.82 25.59 Total 27 751.43 Variate: Fruit width June Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 93.08 46.54 2.56 0.087 Residual 52 945.79 18.19 Total 54 1038.87 Variate: Fruit width July Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 21.88 10.94 0.57 0.572 Residual 30 576.35 19.21 Total 32 598.24 University of Ghana http://ugspace.ug.edu.gh 73 Shade Variate:Fruit width May Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 48.70 24.35 0.96 0.390 Residual 58 1475.75 25.44 Total 60 1524.45 Variate: Fruit width June Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 22.57 11.29 0.44 0.649 Residual 27 694.36 25.72 Total 29 716.93 Variate: Fruit width July Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 28.03 14.02 1.04 0.382 Residual 13 175.46 13.50 Total 15 203.50 University of Ghana http://ugspace.ug.edu.gh 74 FRUIT WEIGHT Control Variate: fruit weight May Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 238.84 119.42 2.31 0.118 Residual 28 1450.21 51.79 Total 30 1689.05 Variate: Fruit weight june Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 146.24 73.12 3.16 0.050 Residual 55 1273.69 23.16 Total 57 1419.93 variate: Weight july Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 47.07 23.54 0.70 0.505 Residual 29 974.59 33.61 Total 31 1021.66 University of Ghana http://ugspace.ug.edu.gh 75 Shade Variate: Fruit weight may Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 79.83 39.91 0.74 0.482 Residual 58 3130.87 53.98 Total 60 3210.70 Variate:Fruit weight june Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 13.80 6.90 0.21 0.809 Residual 27 870.57 32.24 Total 29 884.37 Variate: Fruit weight july Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 18.77 9.38 0.46 0.638 Residual 13 262.46 20.19 Total 15 281.23 University of Ghana http://ugspace.ug.edu.gh 76 FRUIT LENGTH Control Variate: Fruit length may Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 429.20 214.60 5.11 0.014 Residual 25 1050.93 42.04 Total 27 1480.13 variate: Fruit length june Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 310.00 155.00 4.67 0.014 Residual 52 1725.31 33.18 Total 54 2035.31 Variate: Fruit length july Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 11.77 5.89 0.28 0.756 Residual 30 625.87 20.86 Total 32 637.64 University of Ghana http://ugspace.ug.edu.gh 77 SHADE Variate: Fruit length May Source of variation d.f. s.s. m.s. v.r. F pr. cultivar 2 172.26 86.13 1.83 0.170 Residual 58 2735.29 47.16 Total 60 2907.55 Variate: Fruit length june Source of variation d.f. s.s. m.s. v.r. F pr. cultivar 2 174.90 87.45 2.38 0.112 Residual 27 991.64 36.73 Total 29 1166.55 Variate: Fruit length july Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 75.51 37.75 2.80 0.098 Residual 13 175.53 13.50 Total 15 251.04 University of Ghana http://ugspace.ug.edu.gh 78 LEAF AREA control Variate: Leaf area May Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 8608.5 4304.3 6.50 0.006 Residual 21 13897.3 661.8 Total 23 22505.8 Variate: Leaf area June Source of variation d.f. s.s. m.s. v. r. F pr. Cultivar 2 12931.3 6465.7 13.92 <.001 Residual 21 9754.9 464.5 Total 23 22686.3 Variate: Leaf area July Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 14196.3 7098.2 22.58 <.001 Residual 21 6601.6 314.4 Total 23 20798.0 University of Ghana http://ugspace.ug.edu.gh 79 shade Variate: Leaf area may Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 12561.8 6280.9 22.83 <.001 Residual 21 5776.6 275.1 Total 23 18338.4 Variate: Leaf area June Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 5474.4 2737.2 5.53 0.012 Residual 20 9900.6 495.0 Total 22 15375.0 Variate: Leaf area july Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 1095.5 547.8 1.13 0.345 Residual 19 9235.6 486.1 Total 21 10331.1 University of Ghana http://ugspace.ug.edu.gh 80 LEAF HEIGHT Control Variate: leaf height May Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 368.52 184.26 14.70 <.001 Residual 21 263.31 12.54 Total 23 631.83 Variate: leaf height June Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 15.01 7.51 0.72 0.498 Residual 21 218.51 10.41 Total 23 233.52 Variate: leaf height July Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 27.90 13.95 1.35 0.280 Residual 21 216.59 10.31 Total 23 244.49 University of Ghana http://ugspace.ug.edu.gh 81 Shade Variate: leaf height May Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 541.64 270.82 26.04 <.001 Residual 21 218.37 10.40 Total 23 760.02 Variate: leaf height June Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 74.78 37.39 2.75 0.088 Residual 20 272.12 13.61 Total 22 346.89 Variate: leaf height July Source of variation d.f. s.s. m.s. v.r. F pr. Cultivar 2 240.777 120.389 13.97 <.001 Residual 19 163.677 8.615 Total 21 404.455 University of Ghana http://ugspace.ug.edu.gh