Varietal range in transpiration conductance of flowering rice panicle and its impact on panicle temperature

Abstract

Transpiration from rice (Oryza sativa L.) panicles can help lower the temperature of the panicle (T p), 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 (g pI), we measured g pI at the time of flowering in the open field in 21 rice varieties of widely different origins. We observed a difference in g pI 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 T p and air temperature (T a) (ΔT p, T p - T a) using a micrometeorology model, where T a was given as 28°C or 35°C. The varietal range in g pI was estimated to correspond to the range of 2.1°C in ΔT p under a humid atmospheric condition and the range of 3.5°C in ΔT p under a dry atmospheric condition. The estimated ΔT p ranges due to varieties may be useful for improving heat avoidance capacity under excessive heat at the critical stage. The sensitivity analysis of ΔT p to ranging g pI suggested that g pI higher than the highest g pI observed in this study may not be effective for additional cooling of T p. Thus, the target of improvement in g pI against HISS should be set at the level of the existing varieties with the highest g pI.