Abstract: A new kind of apetalous mutant male sterility line, AMS971, was discovered in apetalous oilseed rape AP197 (Brassica napus). The male-sterile trait was genetically controlled by four pairs of recessive nuclear genes. The AMS971 flower consists of four sepals, six carpelloid stamens without anthers and a normal carpel in the center of the flower. The top to base of the third-whorl carpelloid stamens showed stigmatic papillae-like inversed-U and semi-fusion carpels with 4~14 exposed ovules. Compared with the wild-type, AMS971 showed 0~4 smaller nectarines, which is similar to AP197. Moreover, the size and weight of the floral organ in AMS971 differs from that in AP197. It was deduced that the AMS971 mutant was caused largely by B-class mutation from genes such as Arabidopsis thaliana.

Key words: Brassica napus, Apetalous mutant sterile (AMS), Floral organ, Carpelloid stamens