Source of resistance against Ralstonia solanacearum in fertile somatic hybrids of eggplant (Solanum melongena L,) with Solanum aethiopicum L

Solanum aethiopicum is reported to carry resistance to bacterial wilt disea se caused by Ralstonia solanacearum which is one of the most important dise ases of eggplant (Solanum melangena). These two species can sexually be cro ssed but the fertility of their progeny is very low. In order to transfer t he resistance and improve the fertility, somatic hybrids between S. melonge na cv. Dourga and two groups of S. aethiopicum were produced by electrical fusion of mesophyll protoplasts. Thirty hybrid plants were regenerated. Whe n transferred to the greenhouse and transplanted in the field, they were vi gorous and showed intermediate morphological traits. Their ploidy level was determined by DNA analysis through flow cytometry, and their hybrid nature was confirmed by examining isozymes and RAPDs patterns. Chloroplast DNA mi crosatellite analysis revealed that 18 hybrids had the chloroplasts of the eggplant and 12 those of the wild species. The parents and 16 hybrids were evaluated in the field for their fertility and resistance to bacterial wilt using a race 1, biovar 3 strain of R. solanacearum. All hybrids were ferti le and set fruit with viable seeds. Their yield was either intermediate or as high as that of the cultivated eggplant. Both groups of S. aethiopicum w ere found tolerant to R. solanacearum, as about 50% of plants wilted after 8 weeks. The cultivated eggplant was susceptible with 100% of willed plants 2 weeks after inoculation. All somatic hybrids tested were as tolerant as the wild species, except six hybrids showing a better level of resistance. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.