Male fertility and freezing tolerance of hybrids involving Solanum tuberosum haploids and diploid Solanum species

Male sterility of (haploid x species) hybrids often hampers the exploitation of wild Solanum species in breeding for cold tolerance. In a study aimed at finding ways round these problems, we found that one accession of the cold tolerant wild species S. sanctae-rosae gave progenies segregating for male fertility in crosses with tuberosum haploids. Moreover, a source of male fertility restorer gene(s) was hypothesized in the (haploid x species) hybrid UP88-C80 (tbr x chc). A relatively high freezing tolerance was found in the progenies coming from tuberosum haploid x sanctae-rosae crosses and some hybrids showed a freezing killing temperature as low as -5.4 degrees C. Although the most tolerant clones did not shed pollen, at least one clone (Sr6, tbr x set) combined male fertility, 2n pollen production and good freezing tolerance (-3.9 degrees C) and might be directly used in crosses with tetraploid S. tuberosum in order to introgress resistance to low temperature in tuberosum form.