Summary

There has been long-term interest in cytoplasmic male sterility (CMS) in plants because it provides, at least in theory, a means to produce commercial quantities of hybrid seed for plants where this would otherwise be difficult or impossible. CMS has been observed in at least 150 different plant species. CMS systems have traditionally been characterized by the restorer genes required to overcome the CMS and to provide male-fertile progeny in the male-sterile cytoplasm. More recently, CMS systems have been characterized by DNA analysis techniques applied to cytoplasmic organelles that are able to distinguish genetic differences between normal and male-sterile cytoplasms. CMS systems of pollination control have been developed in several major field and horticultural crops. These CMS systems consist of a malesterile female “A-line,” a male-fertile maintainer “B-line,” and a male-fertility restorer “R-line.” There are a number of limitations associated with the use of CMS in the development of hybrid cultivars. Even with these limitations, CMS is the predominant method of pollination control for hybrid seed production for hybrid cultivars throughout the world. Current research is aimed at enhancing our understanding of the molecular basis of CMS and, through this, enhancing our understanding of improving and extending CMS as a pollination control mechanism. Research on future uses of CMS is focused on the development of cytoplasmic gene transformation systems using CMS components.

Introduction

Plants that do not produce viable, functional pollen grains are male sterile. If such male sterility is exclusively maternally inherited, it is described as cytoplasmic male sterility (CMS). Since the first reference to CMS (Bateson and Gairdner 1921), there have been more than seven hundred papers published on CMS in plants.