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

The wild tuber-bearing relative Solanum stenotomum was used as source of re sistance to bacterial wilt caused by Ralstonia solanacearum. In order to tr ansfer resistance, somatic hybrids between a dihaploid clone of potato (S. tuberosum) cv. BF15 and S. stenotomum were produced by electrofusion of mes ophyll protoplasts. A total of thirty hybrid plants were regenerated. When transferred to the greenhouse, they exhibited a strong vigour and showed mo rphological intermediate traits, including leaf form, flowers and tuber cha racteristics. DNA analysis using flow cytometry revealed that 25 were tetra ploids (4x; 48 chromosomes), three hexaploids (6x; 72) and two aneuploids ( < 4x; 48). Their hybrid nature was confirmed by examining isoenzyme pattern s for esterases, and analysis of DNA simple sequence repeat (SSR) markers. Analysis of chloroplast (ct) DNA microsatellites of fourteen somatic hybrid s revealed that six hybrids possessed ctDNA of S. stenotomum, and eight con tained S. tuberosum ct-type. Six tetraploid hybrid clones were evaluated fo r resistance to bacterial wilt by using race 1 and 3 strains of R. solanace arum, originating from Reunion Island. Inoculations were performed by an in vitro root dipping method. The cultivated potato was susceptible to both b acterial strains and died within a few days. Interestingly, all somatic hyb rids tested showed a resistance level as high as that of the wild species. (C) 2001 Editions scientifiques et medicales Elsevier SAS.