Selection for Tolerance of Heat Stress in Soft Red Winter Wheat Using an Artificially Warmed Environment.

Temperature increases for the southeastern United States are projected to range from 1-3°C by 2050. High temperatures are known to affect crop development and breeding for tolerance to heat stress is difficult in field environments. A study investigating the effects of heat stress on soft red winter wheat (Triticum aestivum L.) varieties was conducted during the 2013-2015 growing seasons at the University of Kentucky Spindletop Research Farm in Lexington, KY. Forty genotypes were chosen based on the combination of traits for vernalization and photoperiod sensitivity determined using marker analysis. These genotypes were planted in a randomized complete block design with two replications in two environments, ambient and artificially warmed. To create a warmed environment, heating cables were buried 2.5 cm below the soil surface and connected to a datalogger programmed to maintain a 1-3°C increase in soil temperature based on replicated thermocouple temperature sensors. Heading date, averaged across genotypes, was shifted 5.25 days earlier in the warmed environment compared to the ambient environment across both years (p<0.05). Grain yield, averaged across genotypes, was significantly reduced in the warmed environment by 219.6 kg ha^-1 (p<0.05); however yield response to environment varied among genotypes with several genotypes displaying an increased yield in the warmed environment. Based on these results, selection for tolerance to heat stress has the potential to increase yield due to increased early season tillering and nitrogen utilization but shifts in phenology may increase the risk for late season freeze damage. Additionally, this field screening method shows potential for selecting genotypes that are well adapted to shifts in temperature regionally for incorporation into breeding programs.