Possibility of a Positive Correlation between the Delay of the Meiosis Stage of Pollen Development and the Degree of Male Sterility among Three Alloplasmic Lines of Brassica rapa Containing Diprotaxis muralis Cytoplasm

Abstract

Three alloplasmic lines were established by combining the nucleus of Brassica rapa with the cytoplasm of Diplotaxis muralis. Two alloplasmic lines showing complete male sterile (MS) phenotypes were designated as MS-Yukina and MS-Kabu, whereas one alloplasmic line that releases some pollen grains was designated as partial male sterile (PMS)-Hakusai. To investigate differences in the MS phenotypes, relationship between the length of flower buds and development of young pollen grains was analysed. The length of flower buds containing pollen at the meiosis stage was 1.90-fold (in MS-Yukina), 1.31-fold (in MS-Kabu), and 1.27-fold (in PMS-Hakusai) that of the corresponding maintainer line (N-Yukina, N-Kabu, N-Hakusai). This value was 1.74-fold (in MS-Yukina), 1.48-fold (in MS-Kabu), and 1.22-fold (in PMS-Hakusai) that of D. muralis. These results indicate that the meiosis stage is delayed in all alloplasmic lines compared to their maintainer lines or their cytoplasmic donor. The delay in the meiosis stage was the least pronounced in PMS-Hakusai among the three alloplasmic lines examined. Thus, a positive correlation might exist between the delay of the meiosis stage of pollen development and the degree of male sterility in these alloplasmic lines. Delayed meiosis in pollen might contribute to male sterility in the three alloplasmic lines.