The ability to avoid dehydration is a drought resistance mechanism becoming increasingly more important even in temperate regions. In wheat, dehydration avoidance can be associated with a maintained canopy cooling during dry periods. However, in an average year under temperate conditions, drought periods are rather short which makes it difficult to routinely screen for drought avoidance using canopy temperature (CT). Furthermore, confounding factors such as differences in height, shoot biomass, canopy structure and phenology complicate the interpretation of differences in CT. We aimed to use temporal trends in CT and canopy greenness during short-term drought and heat events in the early grain filling phase to circumvent these problems. During this phase, evaporative demand is high and phenology-driven senescence has yet little effect on CT. Diverse sets of 354 and 71 wheat genotypes where grown in the field phenotyping platform of ETH Zurich in 2018 and 2019, respectively. CT was repeatedly measured during early grain filling by means of drone-based imaging. The temporal trends in CT during early grain filling showed a moderate to high within-year heritability (h² = 0.35 and h² = 0.88 in 2018 and 2019, respectively). These trends were largely independent of confounding factors when compared to single time point measurements and likely represent genotype-specific reactions to decreasing water availability more directly than absolute CT. CT trends were also largely independent of the temporal trends in stay-green indices. Therefore, we used a combination of time-resolved CT and stay-green trends to identify genotypes combining both traits. Significant differences were observed in the combined time-resolved index among three replicated check varieties. We therefore propose to use the combined time-resolved index to identify genotypes with improved drought avoidance and functional stay green.

避免脱水的能力是一种抗旱机制，即使在温带地区也变得越来越重要。在小麦中，避免脱水可能与干旱期间保持冠层冷却有关。然而，在温带条件下的平均年份中，干旱期相当短，这使得使用冠层温度 (CT) 定期筛选避免干旱的情况变得困难。此外，诸如高度、芽生物量、冠层结构和物候差异等混杂因素使 CT 差异的解释变得复杂。我们的目标是在早期籽粒灌浆阶段的短期干旱和高温事件中使用 CT 和冠层绿度的时间趋势来规避这些问题。在这个阶段，蒸发需求很高，物候驱动的衰老对 CT 的影响很小。分别于 2018 年和 2019 年在苏黎世联邦理工学院的田间表型平台上种植的 354 和 71 个小麦基因型的不同组。通过基于无人机的成像，在早期谷物灌浆期间重复测量 CT。灌浆早期 CT 的时间趋势显示出中等至高的年内遗传力（h² = 0.35 和 h ² = 0.88（分别在 2018 年和 2019 年）。与单一时间点测量相比，这些趋势在很大程度上独立于混杂因素，并且可能代表了比绝对 CT 更直接地降低可用水量的基因型特异性反应。CT 趋势在很大程度上也与保持绿色指数的时间趋势无关。因此，我们结合使用时间分辨 CT 和保持绿色趋势来识别结合这两种性状的基因型。三个重复检查品种的组合时间分辨指数存在显着差异。因此，我们建议使用组合时间分辨指数来识别具有改善的干旱避免和功能性保持绿色的基因型。