Male sterility systems for hybrid seed production in Brassica crops.

Abstract Brassica crops are important sources of edible oil, leafy vegetables and renewable energy. In addition, some Brassica crops inhibit potato pests and have the potential to become cash crops from the potato rotation land for potato growers, if these crops yield well. One effective approach to increase Brassica crop productivity per unit land is through the use of the heterosis in hybrids prepared with male sterility systems. In Brassica crops, various male sterility systems have been identified or developed, including endogenous nuclear male sterility (NMS: recessive NMS, dominant NMS, interactive NMS), cytoplasmic male sterility (CMS: endogenous CMS, alloplasmic CMS) and transgenic male sterility. Both environmentally stable and sensitive male sterility systems are available and in use. The chlorosis associated with allochloroplasts in several alloplasmic CMS systems has been largely eliminated by organelle-selective protoplast fusion. Several mitochondrial CMS genes and a CMS fertility restorer gene ( Rfo ) have been identified and sequenced. The cloning of NMS genes and additional CMS fertility restorer genes is underway. The difficulty in maintaining NMS uniformity in populations has been partly solved by the interactive NMS (INMS)-based approach (epistatic suppressors for either recessive or dominant male sterility genes). INMS has become one of the most useful MS systems. This critical review focuses on the types, genetic analysis and technological breakthroughs of Brassica plant male sterility systems for their use in the large-scale hybrid-seed production.