The Early-Morning Flowering Trait of Rice Reduces Spikelet Sterility under Windy and Elevated Temperature Conditions at Anthesis

We previously demonstrated that heat-induced spikelet sterility at anthesis could be mitigated by using an early-morning flowering (EMF) line of Oryza sativa L cv. Koshihikari crossed with wild rice, O. officinalis. Another microclimate factor, high wind velocity, is known to increase the sterility induced by heat. In this study, we evaluated whether EM:F rice could mitigate sterility under the combined stresses of heat and wind. Rice plants were exposed to three levels of wind velocity (1.1, 2.2, 3.4 m s(-1)) from early-morning until 1500 in a glasshouse, where air temperature reached 30 degrees C at 0800, 34 degrees C at 1000 and 38 degrees C around noon. Under these conditions, sterility steadily increased in Koshihikari, ranging from 28.4 to 86.9% as wind velocity increased. However, in the EMF line, low levels of sterility were observed since most spikelets flowered before 1000 when air temperature reached 35 degrees C, the critical value for causing sterility. These results indicated that the increase in heat-induced spikelet sterility by wind can be potentially mitigated by using EMF rice.