Research On Spikelet Sterility Induced By High Temperature In Rice

Heat stress during reproductive stage was one of the prominent factors to reduce rice yield in China.Ⅱyou7954(heat sensitive variety) and Ⅱyou7(heat tolerant variety) were used to study sterilityinduced by high temperature at reproductive stage. The sensitive stage and time from booting toanthesis to high temperature were determined. The effect of high temperature on floweringcharacteristics was studied, and the cause of spikelet sterility was clear. Then effects of hightemperature in the pre-blooming and blooming periods on anther dehiscence, pollen dyeability, pollengrains diameter, pollen germination and tube growth were studied. Effects of water stress and humidityon heat stress were studied, and heat resistance among varieties and the effect of high temperaturesetting mode on evaluation of heat resisitance in rice were discussed. The main results in this study wereas follows:The sensitive stage of spikelets sterility to high temperure at reproductive stage was anthesis stage.The sensitive stage of spikelets sterility to high temperure at anthesis stage was the day at blooming, andthe sensitive time of spikelets sterility to high temperure at blooming was glume opening. Hightemperature setting mode affected the sensitive stage of spikelets sterility to high temperure at anthesisstage, which was the day before blooming when exposing to11:00-16:00heat treatment.High temperature advanced the flowering clock of Ⅱyou7andⅡyou7954, delayed that oflianjing6. Ⅱyou7had obvious flowering peak, yet Ⅱyou7954and lianjing6had low or indistinctflowering peaks. The flowering period of heat tolerant sensitive variety was shortened and the dailynumber of spikelet flowering was more than that of heat sensitive variety. Glume opening time affectedspikelet fertility. Early flowering raised the spikelet fertility both in indica and japonica rice, andflowering after the end of heat stress raised the spikelet fertility of indica rice, not japonica rice. Hightemperature setting mode affected flowering characteristics and spikelet fertility. In contrast with hightemperature during9:00-14:00, the flowering peak of high temperature during11:00-16:00occurredbefore heat stress, then sterility was induced by high temperature before blooming not by hightemperature occurring at blooming, and the sensitive temperature was higher. High temperatureinhibited glume opening for good at anthesis stage, which didn’t take a part in avoiding heat injury.High temperature before blooming didn’t affected the anther dehiscence of varieties whose antherstarting splitting up just after glume opening under moderate temperature, while the pollen sheddingwas still bad, and affected anther dehiscence of varieties whose anther dehiscence was late. Hightemperature at glume opening affected anther dehiscence most seriously, and the temperature beforeglume opening affected that less.Pollen dyeability closely related to the developmental stages. The starch in pollen grains subjectedto high temperature before blooming began to degcompose, and became very few when glume opening.The worse the anther dehiscence, the worse the pollen dyeabilitity was. Temperature at bloomingdestroyed the internal structure of pollen grains, the pollen grains were broke, and the pollen dyeability was bad. Under high temperature, the pollen diameter at one day before blooming began to expand,became largest just before glume opening, then the pollen grains shrived after glum opening. Hightemperature at blooming made pollen shrived, then the diameter of which reduced.High temperature before and at glume opening affected pollen shedding, pollen germination andtube growth. High temperature after glume opening affected tube growth. The earlier the hightemperature came, the lower the spikelet fertility was, and when pollen tube entered into micropyl40min after glume opening, high temperature had no significant effect on spikelet fertility. Hightemperature before blooming affected pollen viability greatly, the starch in pollen grains degraded, andthe length of pollen tube was short.When relative humidity and temperature was high, the VPD was low, stomatal conductancedecreased, transpiration rate decreased, the leaf temperature was high, floral organ suffered severely,pollen shedding was bad, the germinated pollen grains on the stigma were few, and the extension ofpollen tube was bad. When blooming under water and heat stress, stomatal conductance decreased, leaftemperature was high, and floral organ suffered severely. Besides, water stress induced poor heading,late flowering clock, poor proportion of spikelets anthesing, then when the filament elongated the glumedidn’t open, which induced anther shriveled and sterility.The anther of heat tolerant varieties began to split up just after glume opening under moderatetemperature, then the early dehiscence led to good pollen shedding. Early flowering, obvious floweringpeak, high flowering peak, high proportion of spikelets anthesing at the earlier stages during floweringperiod, high proportion of spikelets anthesing under high temperature were found in heat tolerantvarieties. The sterility of heat tolerant varieties occurred at later stages Heat tolerance of varieties wasrelated with their male parents and female parents.