Pre- and post-flowering impacts of natural heatwaves on yield components in wheat

Abstract

Wheat crops are highly sensitive to elevated temperatures and experience significant yield losses when short periods of heat occur at sensitive developmental phases. This research aimed at quantifying wheat responses of grain yield and yield components to heat indicators in fluctuating field conditions. The impacts of high temperature on yield and its components were assessed for 20–35 wheat lines in irrigated multi-environment trials over three years. Genotypes were cultivated using a novel photoperiod-extension method (PEM) adjacent to some conventional yield plots with different sowing dates. In the PEM, either single stems or plant quadrates were tagged at specific growth stages and hand-harvested at maturity, while conventional plots were mechanically harvested at maturity. The impact of heatwaves was estimated for events occurring at different developmental stages and for different temperature thresholds (26–35°C). The strongest correlation between heat and grain number was observed between 300 and 200○Cd before flowering for a threshold temperature of 28°C. For each hot hour (T > 28°C) during this period, wheat genotypes lost on average an extra 0.25 grain at the spike level, and 281 grains m−2 at the canopy level in conventional plots. For individual grain weight, correlations were statistically the closest for threshold temperatures above 32°C post-flowering. In the tested environments, grain number was most sensitive to heat between 300 and 200°Cd before flowering. Each post-flowering hour with T>32°C (between 0 and 500°Cd after flowering) reduced individual grain weight by an average of 0.26 mg at the spike level (PEM spike harvest) and grain yield by 2.44 g m−2 at the canopy level (conventional plot harvest). Impacts of heatwaves were clearest when measured at the organ level (i.e. spikes) and for material with synchronised phenology. In addition, results suggest that heat impacts can also be quantified more reliably using finer time units (i.e. hot hours rather than days). In the studied well-watered conditions, natural heatwaves strongly impacted grain number for temperatures above 28°C and individual grain weight for temperatures above 32 °C. Reductions in grain number and individual grain weight were strongly associated with accumulated hot hours that occurred during 200–300°Cd before and 0–500°Cd after flowering, respectively. The findings from this study will assist improvement for crop modelling in response to heatwaves, development of relevant phenotyping methods and selection of cultivars with better adaptation to warmer environments.

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