DEVELOPMENT OF FRESH MARKET TOMATO (Solanum lycopersicum L.) VARIETIES WITH IMPROVED YIELD, FRUIT QUALITY AND SHELF-LIFE
Tomato (Solanum lycopersicum L.) fruits are naturally perishable and have a short shelf life. Rapid ripening leads to post-harvest losses which is devastating along the tomato value chain. The objective of this study was to develop high yielding tomato varieties with improved fruit quality and shelf life. The study used participatory rural appraisal and surveys to identify preferences and perceptions of stakeholders in the tomato value chain, to develop product profile of fresh market tomato and to make proper breeding choices. The target population included tomato farmers, market players and consumers. Crosses were made between four CSIR/CRI tomato lines and three ripening mutant lines to develop populations with extended shelf life. The developed F1s were further assessed for their hybridity using SNP-based markers to detect the shelf life genes rin, nor, alc. The tomato line CSIR/CRI-AT06 was crossed with Alc-LA3134 to develop an F2 population for use in identifying a single nucleotide polymorphism (SNP) marker associated with the alc gene conferring extended shelf life in tomato. An assessment of the Sly10-14 SNP marker was completed by comparing SNP score against fruit shelf life of the 72 F2 entries. The pattern of segregation of SNP marker for the alc gene was tested for goodness of fit to a 1:2:1 ratio using Chi-square test (χ2) test. Additional cross was made between CSIR/CRI-P002 and Alc-LA3134 to develop six populations and determine the gene effects of the traits studied. These populations were later evaluated and subjected to generation mean analysis. Both heritability and heterosis were estimated for the traits studied. Using marker-assisted backcrossing (MABC), the shelf life gene (alc) was transferred into the genetic background of two elite tomato breeding lines; CSIR/CRI-P002 and CSIR/CRI-ATS06. The MABC derived lines at BC2F3 were further evaluated to confirm selections using molecular markers. Results from the participatory rural appraisal established tomato as the number one vegetable crop produced by the communities where the study was carried out. Over 77 percent (77.5%) of the consumers use tomatoes every day in their food preparation. Of the six important quality traits of tomato mentioned by stakeholders, fruit firmness and shelf life were the most preferred quality traits. Results from the survey validated the objective of the study to develop tomato varieties with extended shelf life. The SNP (Sly10-alc) tested for the alc gene was polymorphic within the seven parental lines, whereas the other SNPs for rin and nor were monomorphic and therefore not useful for the study. The results indicated only one SNP (Sly10-alc) as a functional SNP to detect a shelf life gene. The molecular analysis revealed two superior F1 hybrids (CSIR/CRI-P002 x Alc-LA3134; CSIR/CRI-ATS064 x Alc-LA3134) for the alc gene which were selected for evaluation as lines for improvement. The SNP marker (Sly10-14) segregated in the expected 1:2:1 Mendelian ratio. The 72 F2 population plants indicated that Sly10-14 had significant association with shelf life at 1% significance level. The marker has an effect of increasing shelf life by 22 days and explains 87% of the observed variation. The mean performance of F1 plants was higher than the mid-parent values for all traits studied except total soluble solids. The additive-dominance model was adequate for explaining the expression of shelf life. The rest of the traits studied showed epistasis. The generation mean analysis indicated that additive, dominance and epistatic gene effects were significant for most of the traits studied. The traits that exhibited epistasis generally showed duplicate epistasis type. A considerable increase in the shelf life value was observed among the MABC derived lines. MABC derived lines or individuals with extended shelf life and superior fruit quality were identified in the study. The introgression of the alc gene into cultivated tomatoes for extended shelf life could reduce post- harvest losses of tomato in Ghana. The high proportion of fixable and non-fixable gene effects exhibited by the traits can be improved through pure line breeding and heterosis respectively.