Creating interspecific hybrids with improved cold resistance in Fragaria

The 12 interspecific hybridization combinations in Fragaria were performed to select promising individuals with improved cold resistance. The interspecific hybrids were obtained from the six combinations of Chandler (8x) × F. viridis (2x), Toyonoka (8x) × F. viridis (2x), Chandler (8x) × F. orientalis (♂) (4x), YH15-10 (12x) × F. orientalis (♂) (4x), AY175 (10x) × F. moschata (♂) (6x) and F. moschata (♀) (6x) × YH15-10 (12x), while failed in their reciprocal crosses. The chromosome number, morphological character and cold resistance of the interspecific hybrids and their parents were investigated. Five ploidy hybrids, including pentaploid (2n = 5x = 35), hexaploid (2n = 6x = 42), octaploid (2n = 8x = 56), enneaploid (2n = 9x = 63) and decaploid (2n = 10x = 70) were obtained. Only one ploidy hybrid was observed in each combination, except for the combination of YH15-10 × F. orientalis (♂), in which two ploidy hybrids (8x and 10x) were obtained. The identified chromosome number indicated that all of the observed individuals were true hybrids. Compared with the parents, most of the hybrids showed intermediate phenotype. The strong aromatic individuals were obtained, although most hybrids were sterile. The fertility of the hybrids from YH15-10 × F. orientalis (♂) was better than that of the other five combinations. Majority of the hybrids exhibited stronger cold resistance than lower cold resistant parent. For instance, 80.00% and 83.33% hybrids respectively from Toyonoka × F. viridis and Chandler × F. orientalis (♂) revealed superior cold resistance than the lower cold resistant parents 'Toyonoka' and 'Chandler'. The five ploidy interspecific hybrids (5x, 6x, 8x, 9x and 10x) with strong cold resistance obtained in this study were valuable resources for strawberry cultivar improvement.