Cytological and genetic characterisation of dominant GMS line Shaan-GMS in Brassica napus L.

Genic male sterility (GMS) is an effective pollination control system applied in the hybrid breeding of Brassica napus L. Shaan-GMS is a spontaneous mutant of dominant GMS in B. napus. In this research, anther abortion in the homozygous two-type line 9A15AB derived from Shaan-GMS was characterised with the combined use of light microscopy and transmission electron microscopy. Results indicated that the most striking differences between the fertile and sterile plants occurred in the tapetum in the early microsporocyte stage. In sterile plants, the tapetal cells were irregularly arranged, multi-layered and occupied the growing space of microsporocytes. When entering into meiosis, the tapetum cells degraded and the cytoplasm fused. Some oval monolayer or bilayer membrane organelles existed in the tapetal cells in sterile anthers. Mitochondria in the tapetal cells were abnormal, and middle layer cells degraded early. Pollen mother cells of Shaan-GMS degenerated at the start of meiosis and ceased at the anaphase I stage, with no dyads or tetrads formed. The combined effects of the abnormal development of the tapetum, the middle layer cells and meiosis lead to male sterility in Shaan-GMS. Inheritance of male sterility of Shaan-GMS is controlled by a monogenically multiallelic locus with three different alleles (Ms, ms and Mf), with a relationship expressed as Mf > Ms and Ms > ms. The findings help lay the foundation for illustrating the mechanism of male sterility and the utilisation of Shaan-GMS in rapeseed.