Inheritance of bacterial wilt (ralstonia solanacearum) resistance among wild tomato (solanum pimpinellifolium) and cultivated tomato (solanum lycopersicon l.) germplasm in Kenya

Abstract

Tomato (Solanum lycopersicon L.) is the second most important vegetable crop after potato in the world. In Kenya, the crop is ranked high as the most important in the horticultural industry. Tomato production is adversely affected by both abiotic and biotic stresses. Among the biotic stresses, bacterial wilt caused by Ralstonia solanacearum is a major disease of tomato causing high reduction in yield and income to farmers in Kenya. The objectives of this study were (i) to identify novel sources of resistance to bacterial wilt from wild tomato germplasm (ii) to determine the mode of gene action controlling bacterial wilt resistance and heritability of the disease in tomato. Two experiments were carried out in the greenhouse at Egerton University in the Department of Horticulture and Soils. In the first experiment, thirty-six tomato genotypes were evaluated for resistance to bacterial wilt in an alpha lattice design of four blocks with ten experimental units per block in two replications for two cropping cycles. In the second experiment, eight parents were crossed in North Carolina II mating design to generate sixteen F1 hybrids. The F1 hybrids were evaluated alongside the eight parents for bacterial wilt in an alpha lattice design of four blocks with six experimental units per block in two replications for cropping two cycles. In the first experiment, significant (p ≤ 0.001) main effects and interactions were found for all traits measured at 30, 45 and 60 days after inoculation (DAI) except cycle effects for plant survival at 30 DAI and genotype × cropping cycle interaction effects for disease incidence at 45 DAI which were significant at (p ≤ 0.05) and (p ≤ 0.01) respectively. Among the genotypes tested for bacterial wilt, KK acc I, NRB, KK acc II, KISII, BRNG acc II and KLF acc III out of thirty-six were resistant with AUDPC value of 0. Cultivar superiority measure based on AUDPC ranked genotypes KK Acc I, NRB, KK Acc II, KISII, BRNG Acc II and KLF Acc III. In the second experiment, testers main effects were significant (p ≤ 0.01) for AUDPC, disease incidence and plant survival. Lines × testers interaction were significant (p ≤ 0.001) for AUDPC and disease incidence. Narrow sense heritability estimates of 0.14, 0.16 and 0.20 obtained for AUDPC, disease incidence and plant survival signified that the expression of disease resistance for the traits was dependent on dominance gene action. General predictability ratio of 0.27, 0.29 and 0.50 for AUDPC, disease incidence and plant survival signified the predominance of non-additive genetic variance compared to additive variance in controlling bacterial wilt resistance. The sources of resistance obtained from this study will be deployed in the breeding programmes aimed at developing resistant tomato varieties.