Male Sterility In Soybean-An Overview

The most common type of reproductive mutations observed in the soybean [Glycine max (L.) Merr.] are those that induce male sterility. The high frequency of occurrence of male-sterile mutations indicates that a number of genes influence the processes of microgametogenesis and microsporogenesis. The current knowledge of these mutations is summarized. The origins of male-sterile mutations, their inheritance patterns, and known linkage relationships are detailed. The phenotypic expression of male-sterile mutations, including their effects on both male and female reproduction, is discussed. The influence of environment on the expressivity of malesterile mutations, and the effects of male-sterile mutations on physiological processes (senescence and nitrogen fixation) are summarized. Male-sterile mutations have been useful in the study of soybean reproduction, genetic and cytogenetic investigations, and in evaluating the potential for commercial production of hybrid soybeans. These various applications of male-sterile mutations are presented. SEED PRODUCTION by self-pollinated crops is dependent upon concerted development of both male and female reproductive structures, and successful pollination and fertilization. Genetic mutations that inhibit developmental processes within either stamens or pistils can result in reproductive sterility. Sterility-inducing mutations of soybean [Glycine max (L.) Merr.] are of two types. Male-sterile, femalefertile (MS-FF) mutations selectively eliminate male reproductive function while female reproductive capacity either is unaffected or is only slightly reduced. Male-sterile, femalesterile (MS-FS) mutations virtually abolish both male and female reproduction. Such mutations are fundamentally different from Fl sterility observed in interspecific hybrids within the genus Glycine. Reproductive sterility in such hybrids arises through the failure of homologous chromosome pairing during meiosis and is not a consequence of single gene mutations (Newell and Hymowitz, 1983). MSFF and MS-FS mutations arise through mutations in single Mendelian loci. These mutations might induce the failure of homologous chromosome pairing during meiosis, but do so through the absence of a specific gene product. ' Received for publication 9 February 1987; revision accepted 26 August 1987. Joint contribution: Agricultural Research Service, U.S. Department of Agriculture, and Journal Paper No. J12771 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011. USDA Project 2763. Portions of this work were completed by RAG while employed by Monsanto Agricultural Company, St. Louis, MO. The authors thank an anonymous reviewer for helpful comments on the manuscript. Interspecific F l sterility in Glycine likely arises as a consequence of genome diversification between the contributing parents. More than 95 % of the seed produced by wildtype soybean plants is the result of autogamy, though the soybean flower has retained features that render it attractive to insect pollinators (Erickson, 1975; Erickson and Garment, 1979). In plants carrying MS-FF mutations, seed production is possible if insect vectors and pollen donors are available. In contrast, soybean plants carrying MS-FS mutations rarely set seed. Sterility in such plants either is due to abnormalities of floral organogenesis that prevent both autogamy and allogamy (Johns and Palmer, 1982) or to the interruption of homologous pairing of chromosomes during meiosis through asynapsis or desynapsis (Hadley and Starnes, 1964; Palmer, 1974a; Palmer and Kaul, 1983). Seed production by such plants may occur through the infrequent formation of eggs with a complete, or nearly complete, chromosome complement as a consequence of nuclear restitution. The absolute sterility of MS-FS types limits their potential for application to soybean breeding and genetics. However, the few viable ovules produced by these mutants often generate aneuploid or polyploid seedlings (Palmer 1974b; Palmer and Heer, 1976) useful in linkage analyses. MS-FF lines are of greater utility because the potential for the generation of seed via outcrossing is retained. Consequently, the intent of this discussion is to summarize the available knowledge regarding MS-FF soybean plants. It is hoped that this will allow researchers to select the mutation best suited to their