Use of Solanum stenotomum for introduction of resistance to bacterial wilt in somatic hybrids of potato

Abstract The wild tuber-bearing relative Solanum stenotomum was used as source of resistance to bacterial wilt caused by Ralstonia solanacearum . In order to transfer resistance, somatic hybrids between a dihaploid clone of potato ( S. tuberosum ) cv. BF15 and S. stenotomum were produced by electrofusion of mesophyll protoplasts. A total of thirty hybrid plants were regenerated. When transferred to the greenhouse, they exhibited a strong vigour and showed morphological intermediate traits, including leaf form, flowers and tuber characteristics. DNA analysis using flow cytometry revealed that 25 were tetraploids (4×; 48 chromosomes), three hexaploids (6×; 72) and two aneuploids ( S. stenotomum , and eight contained S. tuberosum ct-type. Six tetraploid hybrid clones were evaluated for resistance to bacterial wilt by using race 1 and 3 strains of R. solanacearum , originating from Reunion Island. Inoculations were performed by an in vitro root dipping method. The cultivated potato was susceptible to both bacterial strains and died within a few days. Interestingly, all somatic hybrids tested showed a resistance level as high as that of the wild species.