ABSTRACT
An effort to obtain a tomato cultivar that would adapt to high temperature and high humidity condition in the southern part of Nigeria in order to increase tomato yield in this part of the country has been in progress for the past nine years (2000-2008).The research was carried out at the Faculty of Agriculture Research Farm, University of Nigeria, Nsukka located in the derived savanna zone latitude 0.6o52, N, longitude 07o24, E, 447.26 m altitude. Three cultivated tomato varieties (Solanum lycopersicon) Roma VF, Tropica (Derica), Nsukka Local and a wild relative, Solanum pimpinellifolium and their progenies were used in the study for the development of a novel tomato cultivar for commercial production. The results of the frequency distributions of the parents and progenies showed continuous variation in fruit size thus suggesting fruit size in tomato as a polygenic trait that is controlled by multiplicative gene action. Genetic progress made over the generations equally revealed that highest genetic gain was obtained at the F11 generation over all the generations studied with a decline at the F12 generation. Correlation coefficients revealed positive associations between yield and all the yield components in all the generations. Path coefficient analysis showed that number of flowers per plant had the highest direct effect on yield. Principal component analysis had number of flowers per plant and fruits per plant as the highest weighting factors. Genotype by trait (GT) biplot analysis revealed that Roma x Wild out performed the other hybrids for the yield traits measured. The results of different statistical analyses performed rated Roma x Wild as the best genotype among the three cross combinations (Roma x Wild, Local x Wild and Tropica x Wild) that will replace the original parents for adaptability under high humidity environment. Among the agronomic traits studied, number of flowers per plant and number of fruits per plant were of considerable importance, thus selection based on these traits will enhance yield in tomato. The genotype (Roma x Wild) gave higher yield and was more tolerant to high humidity conditions.
TABLE OF CONTENTS
TITLE PAGE
LIST OF CO-AUTHORED PUBLICATIONS
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
ABSTRACT
INTRODUCTION
LITERATURE REVIEW
MATERIALS AND METHODS
Experiment I: Studies on the Inheritance of Fruit Size
Experiment II: Genetic Progress made from F1 to F12 Generation of the
Tomato Hybrids in Four Yield determining Components
Experiment III: Studies on the Relationships of the Advanced
Generations (F7 - F12) of the Three Tomato Hybrids
Experiment IV: Replicated Yield Trial of F12 Populations and the Parents
RESULTS
DISCUSSION
CONCLUSION
REFERENCES
INTRODUCTION
Tomato is one of the most widely grown vegetable crops in the world. Nutritionally, tomato is a significant dietary source of vitamin A and C. It is also a good source of protein. The fruits contain high levels and serve as an important dietary source of vitamin A, B, C, E and nicotinic acid ( Davis and Hobson, 1981). Lycopene in tomato is a powerful antioxidant and reduces the risk of prostrate cancer (Rick, 1980; Giovannucci, 1999). Hundred grams of tomato fruits can supply about 20 to 40 percent of the US recommended daily requirements of vitamins A and C, respectively for adults (Grierson and Kader, 1986).
Tomato is a warm season crop that is sensitive to high temperature and high humidity conditions. It thrives under the temperature range of 15 to 20oC for optimum growth and yield (Villareal, 1980). High humidity creates room for many tomato diseases like tomato leaf curl, damping off, Fusarium wilt, and leaf spot. These diseases cause considerable damage to tomato with serious implications on yield and quality. High temperature limits field production of tomatoes in the tropics. The most serious effect of high temperature is reduction or prevention of fruit set. Under high temperature, low assimilates are partitioned to the reproductive tissue (El Ahmadi and Stevens, 1979). Lack of viable pollen is a major cause of poor fruit set at high temperatures. Kidson and Stantion (1953) observed that high humidity increases the proportion of non- uniformity in fruit coloration in tomatoes. Rao (1986) indicated that high temperature and high rainfall during flowering and fruiting result in reduced leaf area per plant and consequent decrease in fruit yield. At high temperature and high humidity, foliage diseases are rampant and these often result in losses in terms of yield (Uguru and Igili, 2002). Charles and Harris (1972) reported decrease in flower production, reduced fruit size and low stigma receptivity under high temperature.
Tomato supply to consumers in Nigeria is grossly insufficient and the few tomato-canning industries depend mainly on import for processing. This was attributed to the low yield particularly in the region south of 10oN latitude. The production of tomato is largely restricted to the drier savanna ecological belt and fresh fruits produced in this belt are distributed to the other parts of the country.
Although, tomato breeding has undoubtedly been very successful in advanced economies a great deal of effort is needed in the underdeveloped countries in other to develop varieties that are adaptable to the local environmental conditions. Assessments of both local and exotic cultivars under field conditions during the rainy season show very poor performance and low fruit set due to excessive flower and premature fruit abortion (Uguru and Atugwu, 2000). The local tomato variety has poor quality and reduced acceptability in local market but has some level of adaptation. The exotic varieties that are highly cherished have narrow genetic base and yield very poorly in the high humidity environment(Uguru and Atugwu, 2000). They are therefore grown more in the drier parts of Nigeria where there is prolonged dry season and cultivation is supported with irrigation.
Wild species are known to be a source of useful genes, mainly for resistance to diseases, pests and abiotic stresses. Roy et al. (1977) reported that hybridization increases yields from 3.4 to 6.6kg per plant. Hybridization of individuals produced hybrids, which combine the characters from both parents. Recombination of genetic factors following hybridization do occasionally result in the production of new desirable characters, hidden in either of the parents. Cytological studies (Uguru and Atugwu, 2001) have shown that it is possible to produce hybrids between the cultivated tomatoes and the wild relatives by conventional breeding methods. Thus, the major challenge in any tomato breeding program for high humidity conditions is to broaden the genetic base of the acceptable cultivars through the utilization of available land races and wild relatives. The traits under focus include tolerance to high humidity diseases of forest ecology, prolific fruit yield during rainy season, low water content and improved fruit quality with these in mind, this research was set up with the following objectives....
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