Analyses of a Dominant Male‐Sterile Character in Upland Cotton. I. Cytological Studies 1

Cytological observations of microsporogenesis breakdown were used to differentiate a new dominant malesterile character in Upland cotton, Gossypium hirsutum L., from the two known dominant male steriles, Ms 4 and Ms 7 . Unlike the Ms 4 genotype where breakdown is either premeiotic or occurs during early stages of meiosis, and unlike the Ms 7 genotype where the latest reported breakdown in microsporogenesis occurs at the onset of pollen wall formation, the pollen in the new male sterile aborted only after the entire pollen wall, both intine and exine, had been fully developed. Thus, breakdown was consistently postmeiotic although a few sporogenous cells may first degenerate. Compared to normal fertile pollen grains, the sterile grains had a significantly thicker and more intenscly staining intine. They also possessed plugs at germ‐pore regions that failed to stain with toluidine blue. Histochemistry revealed these plugs were composed of hemicellulose or some complex polysaccharide. Histochemical studies also disclosed a unique layer of insoluble carbohydrate located between the intine and exine walls in the sterile microspores. Cytoplasm disintegrated progressively during pollen development resulting in sterile pollen grains that were conspicuously shriveled and vacuolate at maturity.