Cytological and molecular characterization of BC1 progeny from two somatic hybrids between dihaploid Solanum acaule and tetraploid S. tuberosum

Abstract

Two hexaploid somatic hybrids, DA12-3 (2n = 68) and DA28 (2n = 74), derived from cell fusion between dihaploid Solanum acaule and tetraploid Solanum tuberosum, were crossed with S. tuberosum. Two BC1 families, DA12T and DA28T, were generated, each containing 25 plants. Although the average of somatic chromosome numbers fitted hypothetical numbers assuming equal separation, considerable variation was found: 2n = 54-62 in DA12T and 2n = 58-65 in DA28T. Fifty-two of 80 RFLP single-copy probes generated 108 marker bands specific 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 locus, which had to be heterozygous in dihaploid S. acaule and maintained in homozygous condition in homoeologous chromosomes of tetraploid S. acaule. On average, 73.7% of the chromosomes derived from S. acaule were detected as recombinants, suggesting that frequent homoeologous recombination occurred between S. acaule and S. tuberosum chromosomes. Therefore, S. acaule germplasm can be effectively transferred to the cultivated potato gene pool through backcrossing hexaploid somatic hybrids with S. tuberosum. In both BC1 families, 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 between S. acaule genomes.Key words: hexaploid somatic hybrids, Solanum acaule, homoeologous recombination, RFLP markers.