Sterility and Poor Pollination Due to Early Flower Opening Induced by Methyl Jasmonate

Flower opening in the early morning helps avoid sterility induced by heat stress at anthesis in rice (Oryza saliva L.). A pot experiment was conducted to reveal the effects of methyl jasmonate (MeJA) on flower opening time (FOT), sterility, pollination, and anther dehiscence. Four mmol L-1 MeJA solution (3 mL per panicle) and water, as a control, was applied to the panicles of the japonica type rice cultivar ʹHinohikariʹ at 0900, 1000, or 1100. By photographing flowers at 4-min intervals, we determined the FOT. Flower sterility, pollination, and anther dehiscence were also examined. Application of MeJA solution at 0900 advanced FOT about 2 hr compared with that without application, and 1.5 hr compared with that after application of water. MeJA application at 1000 also advanced FOT, but that at 1100 did not. Application of MeJA solution significantly increased the numbers of flowers opening on the day of treatment and decreased that on the day after treatment. Application of MeJA solution at 0900 significantly increased flower sterility compared with that without treatment. More than 40% of the flowers that were treated with MeJA and opened on the day of treatment were those expected to open on the next day. These results suggest that sterility induced by application of MeJA is caused by the early opening of flowers expected to open the day after treatment.