Effects of cytoplasmic-nuclear male-sterility systems on Sorghum grain mold development

Hybrid cultivar development in sorghum [Sorghum bicolor (L.) Moench] became possible with the discovery of cytoplasmic-nuclear male-sterility (CMS) designated as A1 (milo) (Stephens and Holland 1954). Since then large numbers of CMS-based hybrids have been developed and commercialized in countries having a well-developed seed industry, including India and China. Commercial hybrids worldwide are currently based on the A1 CMS system. However, hybrids based on a single CMS system with narrow nuclear genetic diversity of both male-sterile (A-) lines and restorer (R-) lines often become vulnerable to insect pests and diseases as was evident from the outbreak of southern corn leaf blight on hybrids based on a Texas cytoplasm in 1970 (Tatum 1971). It has been shown that the A2 CMS system is a good alternative to the A1 system in terms of the agronomic performance of hybrids (Moran and Rooney 2003; Reddy et al. 2005). However, commercial utilization of non-miloCMS systems depends on several factors including their effects on agronomic traits, and their responses to major diseases and insect pests. In the present study, the effects of A2 cytoplasm on grain mold development are assessed in comparison to A1 and their implications for diversification of CMS-based hybrid parents and their hybrids are discussed