Drought-adaptive attributes in the Seri/Babax hexaploid wheat population

Agronomic and physiological traits associated with drought adaptation were assessed within the Seri/Babax recombinant inbred line population, which was derived from parents similar in height and maturity but divergent in their sensitivity to drought. Field trials under different water regimes were conducted over 3 years in Mexico and under rainfed conditions in Australia. Under drought, canopy temperature (CT) was the single-most drought-adaptive trait contributing to a higher performance (r(2) = 0.74, P < 0.0001), highly heritable (h(2) = 0.65, P < 0.0001) and consistently associated with yield phenotypically (r=-0.75, P < 0.0001) and genetically [R(g)=-0.95, P < 0.0001]. CT epitomises a mechanism of dehydration avoidance expressed throughout the cycle and across latitudes, which can be utilised as a selection criteria to identify high-yielding wheat genotypes or as an important predictor of yield performance under drought. Early response under drought, suggested by a high association of CT with estimates of biomass at booting (r=-0.44, P < 0.0001), leaf chlorophyll (r=-0.22 P < 0.0001) and plant height (r=-0.64, P < 0.0001), contrast with the small relationships with anthesis and maturity (averaged, r=-0.10, P < 0.0001), and with osmotic potential (r=-0.20, P < 0.0001). Results suggest that the ability to extract water from the soil under increasing soil water deficit is a major attribute of drought adaptation. The genetic variation and transgressive segregation suggest further genomic and transcriptomic studies for unravelling the complex relationship between drought adaptation and performance under drought.