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) (Δ
Tp, 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 Δ
Tp under a humid atmospheric condition and the range of 3.5ºC in Δ
Tp under a dry atmospheric condition. The estimated Δ
Tp ranges due to varieties may be useful for improving heat avoidance capacity under excessive heat at the critical stage. The sensitivity analysis of Δ
Tp 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.
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