Cytological and molecular characterization of BC1 progeny from two somatichybrids between dihaploid Solanum acaule and tetraploid S-tuberosum

Two hexaploid somatic hybrids, DA12-3 (2n = 68) and DA28 (2n = 74), derived from cell fusion between dihaploid Solanum acaule and tetraploid Solanum t uberosum, were crossed with S. tuberosum. Two BC1 families, DA12T and DA28T , were generated, each containing 25 plants. Although the average of somati c chromosome numbers Fitted hypothetical numbers assuming equal separation, considerable variation was found: 2n = 54-62 in DA12T and Zn = 58-65 in DA 28T. Fifty-two of 80 RFLP single-copy probes generated 108 marker bands spe cific for S. acaule, by which BC1 progeny were analyzed. The segregation of marker bands from at least 44 probes was explained by two alleles per locu s, which had to be heterozygous in dihaploid S. acaule and maintained in ho mozygous condition in homoeologous chromosomes of tetraploid S. acaule. On average, 73.7% of the chromosomes derived from S. acaule were detected as r ecombinants, suggesting that frequent homoeologous recombination occurred b etween S. acaule and S. tuberosum chromosomes. Therefore, S. acaule germpla sm can be effectively transferred to the cultivated potato gene pool throug h backcrossing hexaploid somatic hybrids with S. tuberosum. In both BC1 fam ilies, S. acaule chromosomes 3, 4, 6, and 11 were detected as recombinants with higher frequencies (84-98%) than those of chromosomes 9 and 10 (60 and 58%, respectively), suggesting that chromosomal differentiation exists bet ween S. acaule genomes.