Development of Durable Resistance in Eggplant to Manage Multiple Strains of the Ralstonia solanacearum Complex for Rootstock Breeding

Bacterial wilt (BW), caused by soil-borne bacteria of the Ralstonia solanacearum species complex (RSSC), is a serious disease affecting eggplant (Solanum melongena) in tropical and subtropical regions. Resistance to BW in eggplant has been identified in several accessions and wild relatives, but no source has shown broad and stable resistance across diverse strains and environmental conditions. In the first screening trial, six eggplant genotypes, including five previously identified as resistant to RSSC, were evaluated along with two tomato checks against eight BW strains representing two phylotypes (I and II) and three biovars (2, 3, and 4). In the second screening trial, 26 hybrids developed from seven parental eggplant genotypes (including the six evaluated genotypes in the first screening plus an additional one) were evaluated, together with the parents, against three BW strains (Pss97, Pss2016, and Pss4). The results showed that the parental line EG048 was highly susceptible, whereas EG44 was resistant to the three strains, with a disease index (DI) of ≤20%. Furthermore, fourteen hybrids were classified as resistant or moderately resistant to the three strains. Among them, hybrid EG27 was categorized as highly resistant to all three strains with a disease index of 5.6–7.3%. In addition, three hybrids (EG8, EG20, and EG29) were highly resistant or resistant to all three strains, with a disease index of 3.8–15.8%. A strong positive correlation was observed between wilting percentage and disease index in the eggplant hybrids across the tested strains. Our results provide valuable support for eggplant breeding programs aimed at developing hybrid rootstocks with broader and potentially broad-spectrum resistance to RSSC in tomato and eggplant.