Resistance to bacterial wilt in somatic hybrids between Solanum tuberosum and Solanum phureja

Somatic hybrid plants were produced after protoplast electrofusion between a dihaploid potato, cv. BF15, and a wild tuber-bearing relative, Solanum ph ureja, with a view to transferring bacterial wilt resistance into potato li nes. A total of ten putative hybrids were selected. DNA analysis using flow cytometry revealed that six were tetraploids, two mixoploids, one amphiplo id and one octoploid. In the greenhouse, the putative hybrids exhibited str ong vigor and were morphologically intermediate, including leaf form, flowe rs and tuber characteristics. The hybrid nature of the ten selected plants was confirmed by examining isoenzyme patterns for esterases and peroxidases , and analysis of RAPD and SSR markers. Analysis of chloroplast genome reve aled that eight hybrids possessed chloroplast (ct) DNA of the wild species, S. phureja, and only two contained Solanum tuberosum ct type. Six hybrid c lones, including five tetraploids and one amphiploid, were evaluated for re sistance to bacterial wilt by using race 1 and race 3 strains of Ralstonia solanacearum, originating from Reunion Island. Inoculations were performed by an in vitro root dipping method. The cultivated potato was susceptible t o both bacterial strains tested. All somatic hybrids except two were tolera nt to race 1 strain, and susceptible to race 3 strain. Interestingly, the a mphiploid hybrid clone showed a good tolerance to both strains. (C) 2000 El sevier Science Ireland Ltd. All rights reserved.