Molecular marker-assisted introgression of the wild Solanum commersonii genome into the cultivated S-tuberosum gene pool

A breeding scheme involving ploidy and EBN manipulations was set up to overcome the interspecific barriers existing between the cultivated Solanum tuberosum and the wild species S. commersonii. Three backcross generations were obtained that were analyzed by means of molecular markers in order to verify the occurrence of recombination between homeologous chromosomes, the extent of the wild genome carried in each backcross, and the efficiency of introgressing useful genes. Twenty commersonii-specific RFLPs provided evidence for recombination on 5 out of 12 chromosomes; for the others no more than 1 commersonii-specific marker was found. Thirty-four commersorzii-specific RAPDs and 61 commersonii-specific AFLPs were used to estimate the wild genome content in the BC,, BC,, and BC(3) generations. The mean value of commersonii-specific markers was 91% and 91% in the BC(1), 74% and 76% in the BC(2), and 31% and 26% in the BC(3) using RAPDs or AFLPs, respectively. Efficiency of the breeding scheme was evaluated by monitoring across these progenies the introgression of S. commersonii resistance to tuber soft rot caused by Erwinia carotovora. Eleven and five resistant genotypes were found among BC, and BC, hybrids, respectively The same progenies were also evaluated for chromosome number and tuber traits. For all analyzed traits except stolon length, all BC, and BC, hybrids resembled the tuberosum type. In order to choose the best genotypes to obtain the following backcrosses, we performed, in each generation, a negative molecular-assisted selection against the wild genome combined with selection for resistance to Erwinia spp. and other traits.