A Set of Molecular Markers to Accelerate Breeding and Determine Seed Purity of CMS Three-Line Hybrids in Brassica napus

Cytoplasmic male sterility (CMS) is the main mechanism employed to utilize the heterosis of Brassica napus. CMS three-line rapeseed hybrids have dramatically enhanced yield and brought about the global revolution of hybrid varieties, replacing conventional crop varieties. Over the last half century, China has led the development of hybrid Brassica napus varieties. Two sterile lines, polima (pol) and shaan 2A, were of particular importance for the establishment of three-line hybrid systems in rapeseed, which has opened up a new era of heterosis utilization. However, in current breeding practices, it takes up to three years to identify the restorer or maintainer relationship and the cytoplasmic type of any inbred material. This greatly affects the breeding speed of new varieties and inhibits the rapid development of the rapeseed industry. To address this problem, we developed a set of molecular markers for the identification of fertile cytoplasmic gene N and sterile cytoplasmic gene S, as well as for the fertile nucleus gene R and sterile nucleus gene r, based on differences in the gene sequences between the CMS line, maintainer line and restorer line of Brassica napus. Combining these markers can accurately identify the CMS line, maintainer and restorer of both the pol and shaan systems, as well as their hybrids. These markers can not only be used to identify of the maintainer and restorer relationship of inbred materials; they can also be used as general molecular markers to identify the CMS-type hybrid purity of pol and shaan systems.