Hard red winter wheat (HRWW) is a major crop in the U.S. Great Plains. Texas A&M AgriLife Research has a productive winter wheat breeding program. Our cultivars (TAM prefix) are widely grown in both dryland and irrigated systems in the HRWW region and have been used as parental germplasm by wheat breeding programs worldwide.

Two of our most popular cultivars, TAM 111 and TAM 112, have been cultivated over one million hectares annually. Although TAM 111 and TAM 112 have both been documented with drought tolerance characters, the physiological mechanisms of tolerance and yield determination are not fully understood. A population (TX1112) containing 124 F5:7 recombinant inbred lines (RILs) was developed from the cross of TAM 112/TAM 111. The objective of this study was to identify physiological traits related to drought tolerance and yield in TX1112 population.

The population was grown in 13 environments with combinations of years (2011-2017), locations, and soil water regimes (dryland, limited irrigation, and full irrigation) in the Southern Great Plains. Traits evaluated included heading date, plant height, biomass at maturity, harvest index (HI), three major yield components (spikes/m2, seeds/spike and thousand-kernel weight, TKW), some early-stage traits, carbon reserve remobilization, and canopy temperature during grain filling.

Wheat grain yield varied largely among environments and genotypes. Water regime is the main factor affecting yield among the environments, in which yield ranged from 0.33 Mg/ha under severe drought to up to 7.12 Mg/ha under full irrigation. In general, plant height is positively correlated to yield, and early heading lines had yield advantage under drought.

Although both biomass and HI contributed to higher yield in genotypes, biomass is more related to yield than HI under drought conditions. Biomass at maturity explained 80% of yield variation under drought. Biomass at anthesis is also correlated to yield. At high water level, yield is related to spikes/m2 and seeds per spike, not related to TKW. Under drought stress, all three yield components contributed to higher yield. Among the early-stage traits, biomass, NDVI and canopy height at jointing stage were positively correlated to yield.

In addition, there was a strong negative relationship between yield and canopy temperature during grain filling under drought.