Genic Male Sterility in Cotton: Post-Meiotic Microspore Abortion as a Decisive Factor

Hybrid cotton can be effectively developed by exploiting genetic male sterility (GMS). Establishing male sterile (MS) lines is a significant challenge in plant breeding programmes for F1 hybrid development. A comprehensive look into the cellular mechanism behind GMS is important, since it is still unclear. To better understand the mechanisms of male sterility in a GMS line of Gossypium hirsutum (GMS 4), morphological, cytological and histological analyses of anthers were performed. The results indicate that phenotypic differences between fertile and sterile anthers were anther dehiscence and atrophy. Scanning Electron Microscope (SEM) observations indicate concave, atrophied anthers and immature microspores in the sterile anther’s pollen sacs. The histological study indicates that in the early uninucleate microspore stage, the microspores were degenerated, leading to no pollen formation. Pollen staining experiments showed that fertile pollens had active mitochondria, dense cytoplasm, high quantities of starch in the cytoplasm and callose in the pollen wall. The primary cause of sterility in the GMS line is post-meiotic delayed callose degradation and microspore degeneration. The cellular level understanding of the GMS presented in this study will be helpful in developing the MS lines for hybrid breeding.