Fertility Alteration Characteristics and Cytological Mechanisms of Pollen Abortion in Thermo-Photo-Sensitive Genic Male Sterile Wheat K64S

This study identified the fertility alteration characteristics and cytological mechanisms of the thermo-photo-sensitive genic male sterile (TPSGMS) wheat line K64S. The fertility-sensitive stage of K64S extends from pollen mother cell formation to the tetrad development stage, with critical fertility alteration thresholds of 14–14.5 °C for temperature and 9–9.5 h for daylength. Under low-temperature and short-day conditions, K64S exhibits complete male sterility, whereas it returns to fertility under high-temperature and long-day conditions. Cytological analysis shows that K64S undergoes normal meiosis and successfully forms normal uninucleate microspores. 4′,6-diamidino-2-phenylindole (DAPI) staining revealed the uninucleate microspores failed to form binucleate microspores, with abortion occurring during the late uninucleate stage. Transmission electron microscopy indicates the pollen abortion in sterile K64S arises primarily from premature tapetal degeneration (a form of programmed cell death, PCD), initiated at the pollen mother cell stage, which disrupts nutrient supply and leads to abnormal nuclear division during subsequent microspore development. These findings provide insights into the cytological mechanism of pollen abortion in TPSGMS wheat and may guide hybrid wheat breeding and application.