Abstract: For understanding the mechanism of photoperiodic-sensitive male sterility in rice ( Oryza sativa L. ). The authors have studied the day-length effects on the rice panicle development after the initiation of the secondary branch primordia (SBP). It was found that the long-day illumination after the initiation of SBP not only delayed heading, but also affected the panicle morphology of late japonica rice lines. These effects were not seen in the early indica dee lines. The similarity of the day-length effects after SBP and before the panicle initiation, as well as the synchronization between the above-mentioned effects and the one caused male sterility of PGMR, supported the hypothesis that the photoperiodic-sensitive male sterility in PGMR is consequent upon the failure of male organ development response to the long-day stress by the mutation.

Key words: Rice, Panicle development, Photoperiodic effects