The Use of Cytoplasmic Male Sterility for Hybrid Seed Production

Cytoplasmically inherited male sterility (CMS) results from an interaction between the organellar and nuclear genomes that conditions the failure to produce functional pollen. CMS provides an expedient mechanism to produce large populations of male-sterile plants for commercial F1 hybrid seed production. In cases where the F1 hybrid crop must produce pollen and set seed, male sterility can be reversed by nuclear-encoded restorer-of-fertility alleles. Although the unfortunate epidemic of Southern Corn Leaf Blight on T-cytoplasmic maize revealed the dangers of hybrid-seed production using a single source of CMS, no other genetic vulnerability to disease or stress has been attributed directly to a CMS gene, in spite of the worldwide use of CMS. In some cases, mitochondrial-encoded CMS genes have been linked to undesirable, plastid-encoded traits, and nuclear restorer-of-fertility alleles have been linked to undesirable nuclear-encoded traits, but these linkages were successfully broken by somatic cell genetics and conventional plant breeding, respectively. The use of CMS to produce hybrid seed is very cost effective and has been widely exploited in a plethora of agronomic and horticultural crops. The purpose of this chapter is to list and review the major sources of CMS used commercially to produce hybrid seed.