Abstract: The interspecific hybridization was carried out with diploid , tetraploid , pentaploid , octoploid species in the genus Fragaria as materials. The percentage of fruit2setting was high when the ploidy level of both
parents was same , e. g. , 53. 3 % in the cross of F. viridis (2x) and F. mandschurica (2x) . While the ploidy of both parents was different , the fruit-setting depended to a great extent on whether the ploidy of the female parent was higher than that of the male. If the lower ploidy species was used as the female parent , the seeds would not or hardly be obtained. On the contrary , if the higher ploidy species was used as the female parent , the percentage of setting was relatively high , e. g. , 68. 4 % in the cross of cv. Yuhime (8x) and natural wild line Heilongjiang No. 7 ( 5x) . One nonaploid seedling was obtained from the corss of Yuhime and Heilongjiang No. 7. The
unreduced gamete was postulated according to its ploidy , meioses and the size of pollens of pollens of parents. The seedlings from interspecific hybridization varied greatly. Some maternal seedlings which were assumed to have resulted from apomixis occurred in several cross combinations. Diploid , tetraploid , pentaploid , hexaploid , heptaploid , octoploid , nonaploid seedlings were obtained from the interspecific hybridization , which was helpful to improve the quality , stress and disease resistance of the cultivated strawberry , and also valuable for research in strawberry genetics.

Key words: Fragaria, Strawberry, Interspecific hybridization, Ploidy, Unreduced gamete