Plant Breeding: Male Sterility in Higher Plants - Fundamentals and Applications

Abstract

Under normal conditions, plants undergo a life cycle that consits of an alternating vegetative sporophytic generation and a much-reduced sexual gametophytic generation. During these cycles, seeds germinate, the mature plant organs differentiate, and finally vegetative growth terminates in flower formation, which in principle leads to sepals, petals, anthers, and carpels. Male sterile mutants which cannot produce fertile pollen or functional anthers can often be observed in higher plant species. In this chapter we differentiate between nuclear and cytoplasmicnuclear male sterility (CMS); the latter is particularly useful for production of hybrid seed, which is the main application of CMS. To date, Fl hybrid varieties are produced in most agricultural and horticultural crops. The successful exploitation of heterosis requires a simple and reliable system to produce female parents and perform crosses for the production of hybrid seed. Without a CMS system, male floral organs must be removed mechanically, which is usually not economical nor practical. While nuclear male sterility is based solely on mutations which occur in nuclear genes, CMS is maternally inherited and based on changes in mitochondrial gene expression as influenced by nuclear genes. Importantly, the CMS phenotype may be corrected by nuclear fertility restoration (RF) genes. In the first section, we discuss anther and pollen development and present recent molecular data as well. In the second part, some of the most important CMS systems are presented. Finally, approaches to genetically engineering male sterility in higher plants are discussed. Genetically engineered male sterility may be applied to any crop, including those crops where CMS systems are not available or are unreliable. This area thus has a tremendous potential in plant breeding.