Responses of spikelet fertility to air, spikelet, and panicle temperatures and vapor pressure deficit in rice

Abstract

Along with the rapid temperature rise anticipated in the future, high temperature-induced spikelet sterility is expected to expose a serious problem in rice production. High relative humidity (RH) or small vapor pressure deficit (VPD) that suppresses transpirational cooling of rice panicle is reported to increase high temperature-induced spikelet sterility. For delineating the responses of spikelet sterility to those environmental variables and panicle/spikelet temperature, a series of experiments were conducted in four plastic houses that were controlled to the target temperatures of ambient (AT), AT+1.5℃, AT+3.0℃ and AT+5.0℃ at the experimental farm of Seoul National University (37.27˚N, 126.99˚E), Korea in 2013 and 2014. Three rice (oriza sativa L.) cultivars differing in maturity were grown under ambient temperature plastic house until transferred to different temperature-controlled plastic houses at initial heading stage of each cultivar. Air temperature, solar radiation, VPD, internal temperature of spikelet, and surface temperature of panicle were monitored at an interval of one minute and, for subsequent analysis, averaged over flowering time (09:00-14:00) during seven days after initial heading of panicle. The spikelet fertility showed wide range of variation from 97.3% to 4.6% depending on temperature treatments, years, and cultivars. The standardized partial ridge regression revealed that not only air temperature but also VPD was negatively associated with spikelet fertility. The spikelet fertility was well fitted to logistic equations not only of air temperature, internal temperature of spikelet, and surface temperature of panicle but also of VPD. The model performances showed no clear differences among temperatures employed to the model equations, while the bi-logistic equation model employing air temperature and VPD as independent variables showed the best performance. Our result was contrary to the previous reports that the increase of VPD (low humidity) reduced high temperature-induced spikelet sterility by increasing transpirational cooling of panicle. However, it was inferred that increased VPD under high temperature conditions would accelerate desiccation of anther or pollen during flowering and result in the decline of pollen viability and germination, leading to lower spikelet fertility. Further detailed study is needed to verify VPD effects on spikelet fertility under high temperature conditions.