LEANDER DEDE MELOMEY

DEVELOPMENT OF HIGH YIELDING TOMATO (Solanum lycopersicum L.) LINES WITH RESISTANCE TO TOMATO YELLOW LEAF CURL DISEASE (TYLCD)

 ABSTRACT

Tomato (Solanum lycopersicum L.) is the most important vegetable in Ghana in terms of area under cultivation and consumption, but production is challenged by lack of improved cultivars and the Tomato Yellow Leaf Curl Disease (TYLCD). In Ghana, tomato breeding programmes have focused on evaluation and screening of cultivars for fruit quality and resistance to the TYLCD but very little has been done to improve the crop through breeding. The objective of this study was to introgress TYLCD resistance genes into farmer-preferred tomato cultivars.Tomato farmers were involved in the breeding programme through a Participatory Rural  Appraisal in six tomato growing communities in the Ashanti, Brong Ahafo and Upper East Regions. Farmers identified TYLCD as the most important biotic stress and proposed that TYLCD resistance, high yield and long shelf life must be prioritized in tomato improvement. To identify tomato accessions with farmers’ preferred traits, diversity among 123 assembled germplasm was determined based on morphological traits valued by the fresh market and 348 SNP markers. The 123 accessions were evaluated in an augmented design with 11 accessions and two checks in each of the 11 blocks. However, 119 accessions were used for data analysis. The first five principal components explained 80% of the variation. Fruit shape, ribbing at peduncle end, fruit green shoulders, number of locules, growth type, shape at blossom end, fruits per plant, firmness, reproductive duration, yield and weight per fruit contributed to most of the variation. The accessions were grouped into two clusters with cluster I having 81 accessions and 37 accessions in cluster II. There was one outlier. A total of 338 SNP markers were polymorphic among 96 accessions. There was population overlap though major groupings were observed for PGRRI, UC Davis and improved accessions. The two most widely grown  cultivars; Power Rano and Peto Mech clustered with the improved accessions from Legon, Syngenta, Wienco and Technisem. To identify TYLCD resistant accessions, specific SCAR and SSR markers linked to the known TYLCD resistance genes were used to amplify the presence or absence of the genes in 21 tomato accessions. The accessions were thereafter screened in TYLCD hot spot in a randomized complete block design at Akumadan in the Ashanti Region and Vea in the Upper East Region. The genes ty-5 and Ty-6 were discovered in accession GH9233 (Pimplifolium) and the Ty-6 gene was found in Pimpinellifolium x Wosowoso. Pimplifolium expressed high level of resistance to TYLCD at both Akumadan and Vea. To identify lines with good general combining abilities and specific crosses that show good fruit quality and yield; crosses were made between 5 locally adapted cultivars on one hand with three exotic lines and Pimplifolium each carrying two of the six TYLCD resistance genes, following North Carolina II mating design. The generated 20 F1s were evaluated in the field in a randomized complete block design with three replications. GCA was significant for all traits studied. Peto Mech was a good combiner for fruit quality traits such as fruit length and fruit hardness. AVTO1311 x Peto Mech had positive SCA for fruit hardness. Pimplifolium x Power had the highest significant SCA estimate for fruits per plant. Lorry Tyre had the highest GCA effect for fresh tomato yield. Lorry Tyre x AVTO1311 had the highest yield per plant. Lorry x AVTO1429 had the highest fruit weight. AVTO1311 and AVTO1429 were good general combiners for fruit weight. The observed heterosis for yield and fruit quality together with the TYLCD resistance offer opportunities for the development of new hybrids. To confirm the presence of the TYLCD resistance genes, three primers genotyped 57%, 81% and 67% of Ty2, Ty-3 and ty-5 heterozygous alleles respectively in the F1 plants. F2 population from Power Rano and AVTO1429 were studied for segregation of Ty-2 and Ty3 genes. Seven and three homozygous resistant plants for Ty-2 and Ty-3 respectively genes were identified. This will enable the screening of F3 families in Tomato Yellow Leaf Curl Disease hotspot.