Heat and drought adaptive QTL in a wheat population designed to minimize confounding agronomic effects.

A restricted range in height and phenology of the elite Seri/Babax recombinant inbred line (RIL) population makes it ideal for physiological and genetic studies. Previous research has shown differential expression for yield under water deficit associated with canopy temperature (CT). In the current study, 167 RILs plus parents were phenotyped under drought (DRT), hot irrigated (HOT), and temperate irrigated (IRR) environments to identify the genomic regions associated with stress-adaptive traits. In total, 104 QTL were identified across a combination of 115 traits × 3 environments × 2 years, of which 14, 16, and 10 QTL were associated exclusively with DRT, HOT, and IRR, respectively. Six genomic regions were related to a large number of traits, namely 1B-a, 2B-a, 3B-b, 4A-a, 4A-b, and 5A-a. A yield QTL located on 4A-a explained 27 and 17% of variation under drought and heat stress, respectively. At the same location, a QTL explained 28% of the variation in CT under heat, while 14% of CT variation under drought was explained by a QTL on 3B-b. The T1BL.1RS (rye) translocation donated by the Seri parent was associated with decreased yield in this population. There was no co-location of consistent yield and phenology or height-related QTL, highlighting the utility of using a population with a restricted range in anthesis to facilitate QTL studies. Common QTL for drought and heat stress traits were identified on 1B-a, 2B-a, 3B-b, 4A-a, 4B-b, and 7A-a confirming their generic value across stresses. Yield QTL were shown to be associated with components of other traits, supporting the prospects for dissecting crop performance into its physiological and genetic components in order to facilitate a more strategic approach to breeding.

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 (r2 = 0.74, P < 0.0001), highly heritable (h2 = 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.