Cooler Canopy Contributes to Higher Yield and Drought Tolerance in New Wheat Cultivars

Drought is an important abiotic stress limiting wheat (Triticum aestivum L.) yield in the U. S. Southern High Plains. Although wheat breeding has improved drought tolerance in the area, the physiological traits conferring drought tolerance have not been well understood. Canopy temperature depression (CTD), the difference between air and canopy temperatures, has been suggested as a trait for identifying drought-tolerant genotypes. The objective of this study was to investigate whether a higher CTD is one of the reasons for higher yield in new drought-tolerant cultivars. Field experiments were conducted in five genotypes (TAM 111, TAM 112, TX86A5606, TX86A8072, and Dumas) under dryland conditions in 2009/2010, 2010/2011 and 2011/2012 seasons. The canopy temperature was measured continuously from late jointing to the middle of grain filling, using wireless infrared thermometers. Although CTD varied with sky conditions, growth stage, and time of day, the genotypic variation in CTD was consistent. In general, yield was positively correlated to daytime CTD whether the CTD was used from a single clear day or a season-long mean. However, including Dumas weakened the correlation under severe drought in 2012. The nighttime CTD was not correlated to yield. Two new cultivars (TAM 111 and TAM 112) had up to 2.7 degrees C higher CTD and 31% more yield than other genotypes. Therefore, cooler daytime canopy might be the reason for higher yield in the two new and drought-tolerant cultivars under drought conditions. Further studies are needed to understand the physiological bases of differences in CTD among genotypes.