| Summary: | Global climate change has been forecast to result in significant alterations to current temperature and precipitation patterns in cereal growing regions worldwide. The increased occurrence of elevated temperature stress at anthesis is likely to result in significant yield losses in wheat (Triticum aestivum L.). The ability of plant tissue to depress its temperature has been reported in relation to the canopy but recent work has demonstrated that spike temperature depression (STD) can be assessed in controlled environments (CE). The findings from two consecutive years of potbased CE experiments, a field-based experiment under polytunnel cover and a rhizobox-based experiment, in which the thermal dynamics of the spike and flag leaf under contrasting conditions of elevated temperature and water-deficit stress at anthesis, are reported. Flag leaf temperature depression (FLTD) was significantly greater than STD at anthesis. The data do not demonstrate an increased cooling capacity of the spike in the early stages of anthesis but rather in the latter stages, a phenomenon hypothesized to be primarily associated with the onset of senescence in the canopy. The inconsistent relationship observed between FLTD/STD at anthesis and grain yield (GY) does not currently elucidate whether a failure to depress tissue temperature at anthesis is associated with a yield penalty. The effect of experimental design on the physiological response to abiotic stress at anthesis was explored. The plant-wide distribution of photoassimilates at mid-anthesis was examined. Starch and water-soluble carbohydrate content in the flag leaf, peduncle and glumes was not found to correlate to GY. Further examination of the effects that abiotic stress at anthesis have on the photoassimilate distribution and GY need to take place in field-grown wheat.
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