Abstract
Transpiration from rice (Oryza sativa L.) panicles can help lower the temperature of the panicle (Tp), which is the susceptive organ for high temperature-induced spikelet sterility (HISS). By increasing the transpiration, the heat damage to the panicle predicted to occur due to global warming may be avoided. To examine the possibility of genetic improvement in transpiration conductance of intact rice panicles (gpI), we measured gpI at the time of flowering in the open field in 21 rice varieties of widely different origins. We observed a difference in gpI among the varieties and three series of experiments, ranging from 0.15 to 0.67 cm s-1. We also estimated its impact on the difference between Tp and air temperature (Ta) (ΔTp, Tp - Ta) using a micrometeorology model, where Ta was given as 28ºC or 35ºC. The varietal range in gpI was estimated to correspond to the range of 2.1ºC in ΔTp under a humid atmospheric condition and the range of 3.5ºC in ΔTp under a dry atmospheric condition. The estimated ΔTp ranges due to varieties may be useful for improving heat avoidance capacity under excessive heat at the critical stage. The sensitivity analysis of ΔTp to ranging gpI suggested that gpI higher than the highest gpI observed in this study may not be effective for additional cooling of Tp. Thus, the target of improvement in gpI against HISS should be set at the level of the existing varieties with the highest gpI.
