Interspecific somatic hybrids between Solanum bulbocastanum and S. tuberosum and their haploidization for potato breeding.

Protoplast fusion between incongruent Solanum bulbocastanum and S. tuberosum haploids was accomplished to produce hybrids combining elite traits from both parents. We identified 11 somatic hybrids out of 42 regenerants analyzed through ISSR markers. Some hybrids had loss or gain of fragments compared to the parents, likely due to rearrangements and deletions of chromosome segments after fusion, and/or to somaclonal variation during hybrid regeneration. Increased heterotic vigor for some traits as well as high diversity was observed as the effect of both ploidy and fusion combination. Microsporogenesis analysis indicated the occurrence of multivalent configurations and several meiotic abnormalities, such as chromosomes bridges and various spindle orientations. Since all hybrids were sterile, in vitro anther culture was employed for haploidization as a possible strategy to overcome barriers to hybridizations. Haploids were obtained from all the tetraploid S. bulbocastanum (+) S. tuberosum somatic hybrids tested, although with differences in both the number of embryos per 100 anthers cultured and the number of differentiated green plantlets. This is the first report on the successful production of haploid plants from S. bulbocastanum (+) S. tuberosum hybrids.