Differences between hybrids of Solanum tuberosum L. and Solanum circaeifolium Bitt. obtained from symmetric and asymmetric fusion experiments

Potato plants obtained by symmetric and asymmetric protoplast fusion experi ments with Solanum tuberosum and Solanum circaeifolium were compared and th eir potential use for plant breeding was investigated. For asymmetric hybri disation wild species tissue was irradiated with X-rays. Irradiation enhanc ed regeneration frequency. RFLP analysis showed that both techniques gave a pprox. 95% hybrids among the regenerates. Asymmetric protoplast fusion gave 22% regenerates with a ploidy level between 2x and 4x or 4x and 6x. None o f the regenerates obtained from symmetric fusion had these ploidy levels. The tetraploid hybrids showed good male and female fertility. Male fertilit y was highest for the eutetraploid regenerates. With increasing asymmetry a nd with increasing ploidy level fertility decreased. Berry induction and se ed production were observed for the eutetraploid and, to a lesser degree, f or the hypotetraploid and hypohexaploid hybrids.