Isolation and characterisation of somatic hybrids of diploid Solanum tuberosum and Solanum brevidens and the use of amylose-free starch mutation for detection of introgression

Summary Somatic hybrids of diploid amylose-free (amf) Solanum tuberosum and diploid S. brevidens were made by Poly-Ethylene-Glycol (PEG) or electrofusion methods. For the isolation of interspecific hybrids the use of selection markers (kanamycin and hygromycin resistance) was useful but not essential. In this 2x+2x interspecific combination 4x and 6x somatic hybrids were obtained. Seed set was the best in 4x×4x (S. tuberosum) backcrosses, but seed germination was the best in 6x×4x combinations, using in vitro germination of unripe seeds harvested 25 days after pollination. A high degree of pollen stainability (30–40%) was observed in 7 tetraploid hybrids and very low in all hexaploids. After iodine staining, the recessive amf marker was expressed by a red colour instead of blue, visible in starch-containing cells like columella cells of root tips, (micro)tubers or microspores. As expected, complementation was observed in starch-containing cells of the fusion hybrids. Segregation of the amf marker was clearly observed in microspores of 4x and 6x hybrids. Segregation ratios in the 4x hybrids showed variable recombination frequencies. In the backcross progeny of hexaploid F12-5 with a tetraploid amf mutant one amylose-free recombinant among 67 plants was found, indicating the occurrence of meiotic recombination in the megaspore mother cells.