Expression of freezing tolerance in the interspecific F1 and somatic hybrids of potatoes

The expression of freezing tolerance was examined in interspecific F-1 and somatic hybrids of potatoes using 20 species and 34 different combinations between hardy and sensitive species. In the field, the frost tolerance of h ybrids resembled either that of the hardy parent, the sensitive parent, or the parental mean, depending on the species combination and the genomic rat io (ratio of the number of sets of chromosomes contributed from each parent ). Similar phenomena were observed when the non-acclimated freezing toleran ce (NA) and the acclimation capacity (ACC) (two independent genetic compone nts of freezing tolerance) were evaluated separately under controlled envir onments. In general, the expression level of freezing tolerance was higher in hybrids with more genomes contributed from the hardy parent than from th e sensitive parent. In addition, the effectiveness or combining ability of genes conferring freezing tolerance from the hardy species also showed some influence on the expression of freezing tolerance. All three parameters, n amely NA, ACC and acclimated freezing tolerance (AA) (NA plus ACC), were si gnificantly correlated to the frost tolerance exhibited in the field. This indicates that the controlled freezing test used in this study could provid e a good estimate of field performance. The implications of these results i n breeding for freezing tolerance in potatoes are discussed.