S^sup h^ and S^sub c^-Two Complementary Dominant Genes that Control Self-Compatibility in Buckwheat

Fagopyrum homotropicum Ohnishi, a wild diploid (2n = 2x = 16) species with self-compatibility expressed by homostylic flowers, has been used for improving cultivated buckwheat, F. esculentum Moench, a self-incompatible diploid (2n = 2x = 16) species with heterostylic pin and thrum flowers. Four crosses were made between F. homotropicum and F. esculentum pin flowers, assisted by ovule rescue in vitro, to study the inheritance and interaction of the two breeding systems in the genus Fagopyrum. The presence of homostylic or pin flowers was used to determine the expression of self-compatibility or self-incompatibility, respectively. The segregation ratios of the F^sub 2^ progeny derived from F^sub 1^ single plants, the BC^sub 1^F^sub 1^ generation and the F^sub 3^ progeny derived from homostylic plants were used to study the inheritance of self-compatibility. Five F^sub 2^ populations fit a one-gene 3:1 segregation ratio and did not fit a 9:7 ratio, while the other three F^sub 2^ populations fit a two-gene 9:7 ratio and did not fit a 3:1 ratio. The BC^sub 1^F^sub 1^ and F^sub 3^ progeny segregation confirmed these observations. These results support a two-gene model with three alleles at the first locus S and two alleles at the second locus S^sub c^. The proposed model has S for self-incompatible thrum, S^sup h^ for self-compatible homostyly, and s for self-incompatible pin, with the intrallelic interaction S > S^sup h^ > s at the first locus and S^sub c^ for homostyly and s^sub c^ for pin (S^sub c^ > s^sub c^) at the second locus. The two complementary dominant genes S^sup h^ and S^sub c^ control self-compatibility (homostyly) in F. homotropicum. The one gene or two gene segregation patterns are the result of interspecific crosses with different F. esculentum genotypes. [PUBLICATION ABSTRACT]