Canopy temperature depression at grain filling correlates to winter wheat yield in the U.S. Southern High Plains

Wheat breeding has improved drought tolerance over the years. However, our knowledge on drought tolerance in relation to the diurnal pattern of canopy temperature (CT) and grain yield is limited. A three-season wheat field study ending 2012, 2015, and 2016 was conducted at Bushland, Texas to investigate the relationship between canopy temperature depression (CTD) and yield during the grain filling period. For each season, 20 elite wheat genotypes were grown under dryland conditions, and CT was measured by Smart Crop wireless IRT sensors every 15 min continuously for 12-15 days during mid-grain filling (∼10-25 days after flowering). There was a genotypic variation for CTD regardless of time of the day; however, the variation was more evident during the day time (10:00-18:00 h), with the smallest CTD (i.e., warmer canopy) at 14:00-15:00 h. In a dry season of 2012, TAM 304, TAM 112, Dumas, and Hatcher had greater CTD (i.e., cooler canopy) than other genotypes. In two wet/near normal seasons (2015 and 2016) Duster, TAM 111, TAM 110, TAM 112, and TAM 105 had greater CTD. There was a significant (P < 0.05) positive linear relationship between grain yield and day-time CTD. Hence, a cooler plant canopy during the mid-grain filling in winter wheat appears to be an important indicator of greater drought tolerance and yield under dryland condition. This knowledge may help breeders to conduct high-throughput field phenotyping in large breeding populations.