Studies on the reproductive biology of male-sterile mutants of soybean (Glycine max (L.) Merr.)
The phenotypic effects of three nuclear male-sterile mutants on reproductive biology in soybean (Glycine max (L.) Merr.) were observed by means of light and electron microscopy. The ms2 mutant interrupted microsporogenesis at the tetrad stage. Postmeiotic cytokinesis deliminated tetrads of microspores. Callose dissolution did not occur, and microspores degenerated after depositing primexine and probacullae. Male sterility was associated with, and perhaps induced by, aberrant ontogeny of the tapetal layer;The ms2 mutant also was shown to have a pleiotropic effect on female reproduction. Spontaneous trisomy occurred among progeny at a rate of 2.4%. Aneuploid lines isolated were evaluated for their stability and potential usefulness in the construction of a trisomic series in soybean;The ms4 mutant was shown to inhibit, or render abnormal, developmental processes related to the function of the postmeiotic MMC plasmalemma. The nature of postmeiotic cytokinesis was variable. Frequently, cytokinesis was omitted, or incomplete and/or irregular in orientation. Less often, cytokinesis was normal in orientation, which led to, but did not ensure, the formation of normal pollen. Postmeiotic (PM) cells varied in the degree of pollen wall organization achieved. Pollen-like walls ranged from only random and scattered sporopollenin deposits to stratified walls indistinguishable from normal pollen walls. Plants homozygous for the ms4 allele were able to generate pollen with features identical to those of normal pollen. Thus, the ms4 mutant was considered a partial male-sterile mutant;A spontaneous male-sterile mutant that arose in 'Wabash' soybean was analyzed both genetically and cytologically. The "Wabash male-sterile" mutant was shown to be an independent mutation at the ms3 locus. Despite diverse nuclear backgrounds, the Wabash ms3 (Wms3) and the 'Calland' x 'Cutler' (original) ms3 were characterized by similar phenotypes. Microspores were generated but produced abnormal walls and were not released from callose. Tapetal cells either degenerated prematurely, or accumulated a refractive material that was thought to be sporopollenin.