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 200Cd 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 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 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.

中文翻译：

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自然热浪在开花前和开花后对小麦产量构成的影响


小麦作物对高温高度敏感，当敏感发育阶段出现短暂的高温时，产量会遭受重大损失。本研究旨在量化小麦在波动的田间条件下谷物产量和产量组成部分对热量指标的响应。在三年多的灌溉多环境试验中，评估了 20-35 个小麦品系的高温对产量及其组成部分的影响。使用新型光周期延长方法（PEM）在一些具有不同播种日期的常规产量地块附近培育基因型。在PEM中，单茎或植物方形体在特定的生长阶段被标记并在成熟时手工收获，而传统的地块在成熟时机械收获。热浪的影响是针对不同发育阶段和不同温度阈值（26-35°C）发生的事件进行估计的。在阈值温度为 28°C 的开花前 300 至 200Cd 之间观察到热量与籽粒数量之间的最强相关性。在此期间的每个炎热小时（T > 28°C），小麦基因型在穗部水平平均损失 0.25 粒米，在常规地块的冠层水平平均损失 281 粒米。对于个体粒重，统计上相关性在花后阈值温度高于 32°C 时最接近。在测试环境中，籽粒数对开花前 300 至 200°C 之间的热量最敏感。 T>32°C（开花后 0 至 500°Cd 之间）的花后每个小时，穗水平的单粒重量平均减少 0.26 毫克（PEM 穗收获），冠层产量平均减少 2.44 克（常规地块收获）。 当在器官水平（即峰值）和具有同步物候的材料上进行测量时，热浪的影响最为明显。此外，结果表明，使用更精细的时间单位（即炎热的小时而不是天）也可以更可靠地量化热影响。在所研究的水分充足的条件下，自然热浪强烈影响温度高于 28°C 时的谷物数量和温度高于 32°C 时的单粒重量。籽粒数和单粒重的减少分别与开花前 200-300°Cd 和开花后 0-500°Cd 期间发生的累积高温时间密切相关。这项研究的结果将有助于改进作物应对热浪的模型、开发相关表型分析方法以及选择更好地适应温暖环境的品种。