Traits in Spring Wheat Cultivars Associated with Yield Loss Caused by a Heat Stress Episode after Anthesis

Heat stress resulting from climate change and more frequent weather extremes is expected to negatively affect wheat yield. We evaluated the response of different spring wheat cultivars to a post-anthesis high temperature episode and studied the relationship between different traits associated with heat tolerance. Fifteen spring wheat (Triticum aestivum L.) cultivars were grown in pots under semifield conditions, and heat stress (35/26 degrees C) and control treatments (20/12 degrees C) were applied in growth chambers for 5days starting 14days after flowering. The heat stress treatment reduced final yield in all cultivars. Significant variation was observed among cultivars in the reduction in average grain weight and grain dry matter yield under heat stress (up to 36 % and 45 %, respectively). The duration of the grain-filling period was reduced by 3-12days by the heat treatment. The reduction in the grain-filling period was negatively correlated with grain nitrogen yield (r=-0.60). A positive correlation (r=0.73) was found between the treatment effect on green leaf area (GLA) and the reduction in yield resulting from heat stress. The amount of stem water-soluble carbohydrates (WSC) was not related to treatment effects on grain yield or grain weight. However, the treatment effect on stem WSC remobilization was negatively correlated with reduction in grain-filling duration due to heat stress (r=-0.74) and positively with treatment effect on grain N yield (r=0.52). The results suggest that the effect of the heat treatment on GLA was the trait most associated with yield reduction in all cultivars. These findings suggest the importance of stay green'-associated traits in plant breeding as well as the need for better modelling of GLA in crop models, especially with respect to brief heat episodes during grain filling. There is in particular a need to model how heat and other stresses, including interacting effects of heat and drought, affect duration of GLA after flowering and how this affects source-sink relations during grain filling.