Development Of New Germplasms Resistant To Ralstonia Solanacearum By Protoplast Fusion Of Diploid Potato

Potato (Solanum tuberosum L.) is one of the most important food crops in the world with abundant wild species. Bacterial wilt caused by Ralstonia solanacearum is a devastating disease of potato. Currently, no resistant genes are found in cultivated species. Some wild or related cultivated species known to be resistant or highly tolerant to bacterial wilt cannot be hybridized with cultivated species due to cross incompatibility. Somatic hybridization provides a new approach to make use of these wild recourses. The study aims on incorporation of resistance against bacterial wilt from diploid wild species (S. chacoense) and diploid clone BW2 derived from a 2x hybridization population to dihaploid S. tuberosum (DH1, DH3 and DH4). The major results are as follows:1. Protoplast fusion with BW2 yielded 1432 calli but no plant differenciation wherease the fusion with S. chacoense formed 144 calli from which 20 plants were regenerated, indicating that the callus formation and plant regeneration is genotype-dependent.2. RAPD and ISSR analysis showed that 11 of the 20 regenerants were true somatic hybrids, and the other 9 were regenerated from S. chacoense. Further analysis of ploidy level using flow cytometry demonstrated that 8 of the 11 somatic hybrids were hexaploids, 1 tetraploid,1 heptaploid and 1 mixoploid.3. Analysis of chloroplast and mitochondrial genome indicated that cytoplasmic recombination occured in 7 somatic hybrids. There was preference to the wild parent S. chacoense for the chloroplast inheritance in 10 of the 11 somatic hybrids, wherease the mitochondrial inheritance varied with 6 cultivated type,3 wild type and 2 fused type.4. Proving by the inoculation of the pathogen in vitro, all the somatic hybrids displayed higher resistance level than cultivated parent. Three of them exhibited stronger resistance or tolerance against race 1 of R. solanacearum and 6 displayed no significant difference when compared with the resistance parent, S. chacoense, and the other 2 of the hybrids had moderate resistance level between the parents.