Genetic Basis of Bacterial Wilt Resistance in Tomato (Solanum lycopersicum L.)

Abstract

Bacterial wilt, caused by the Ralstonia solanacearum species complex, is a major constraint to tomato (Solanum lycopersicum L.) production, particularly in warm and humid environments such as Karnataka. The development of resistant cultivars represents an effective, sustainable, and economical strategy for disease management; however, the genetic basis of resistance must be understood to facilitate efficient selection and resistance breeding. The present study was undertaken to investigate the inheritance of bacterial wilt resistance in tomato using the resistant inbred NBT-01 crossed with two susceptible inbreds, NBT-05 and NBT-06. The two crosses, NBT-01 × NBT-05 (Cross-1) and NBT-01 × NBT-06 (Cross-2), were generated, and their parental lines, F₁, F₂, and backcross generations were evaluated for disease reaction under sick-plot conditions. Segregation patterns in the F₂ populations were analysed for conformity with expected Mendelian ratios using chi-square tests. The F₁ plants of both crosses showed a predominantly resistant phenotype, with a PDI of 6.66%, indicating strong expression of resistance from NBT-01. Resistance was dominant over susceptibility in both crosses in the F₂ generation. In NBT-01 × NBT-05, 265 resistant and 15 susceptible plants were recorded among 280 plants, compared with expected frequencies of 262.5 and 17.5 under a 15:1 ratio. The corresponding chi-square value was 0.381 (df = 1; P = 0.537). Similarly, NBT-01 × NBT-06 produced 252 resistant and 13 susceptible plants among 265 plants, compared with expected frequencies of 248.44 and 16.56, giving a chi-square value of 0.817 (df = 1; P = 0.366). Thus, F₂ segregation in both crosses was consistent with a 15:1 resistant:susceptible ratio, suggesting that resistance is governed by the interaction of two dominant genes or loci under the conditions evaluated. These findings provide genetic evidence for a complementary gene action model for bacterial wilt resistance in NBT-01, and the identified inheritance pattern can assist in designing selection strategies for incorporating bacterial wilt resistance into susceptible tomato breeding lines. Nevertheless, the segregation pattern represents the genetic model observed for the specific crosses, pathogen population, and screening environment and does not, by itself, establish the molecular identity of the underlying resistance loci.