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 exploi tation of wild Solanum species in breeding for cold tolerance. In a st udy aimed at finding ways round these problems, we found that one acce ssion of the cold tolerant wild species S. sanctae-rosae gave progenie s segregating for male fertility in crosses with tuberosum haploids. M oreover, a source of male fertility restorer gene(s) was hypothesized in the (haploid x species) hybrid UP88-C80 (tbr x chc). A relatively h igh freezing tolerance was found in the progenies coming from tuberosu m haploid x sanctae-rosae crosses and some hybrids showed a freezing k illing temperature as low as -5.4 degrees C. Although the most toleran t clones did not shed pollen, at least one clone (Sr6, tbr x set) comb ined 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.