The Physiological Basis of Drought Tolerance Identified from Genetic Association Analysis in Wheat (Triticum aestivum L.)

Abstract

Drought remains the single most important abiotic stress reducing wheat grain yield in the Australian wheat belt. This study aimed to (i) elucidate the physiological traits linked to genomic regions conferring higher yield under moisture stress identified in an earlier genetic association analysis (Atta, 2013) and (ii) validate the earlier genetic association analysis. Materials were evaluated under different farming practices including contrasting tillage and irrigation. Mixtures of genotypes based on complementary marker trait associations (MTAs) were included to examine the buffering effects of mixtures on yield and associated traits. The MTAs estimated in the Atta (2013) study were validated in head-to-head comparisons of the same materials in 2014 and 2015 and by developing and testing new germplasm selected on the basis of the significant MTAs for yield. Five traits; days to heading, normalized difference vegetation index, leaf rolling, earliness to ground cover and grain filling duration accounted for 87.8% of the observed variation in yield and could be utilized for indirect selection of genotypes with higher yield and water-use-efficiency. No-tillage rainfed environments produced higher mean grain yield with better water-use-efficiency relative to conventional tillage and no genotype x tillage practice interaction was observed. Some cultivar mixtures produced higher yield relative to their pure line components. No significant improvement in phenotype was noted when progeny carrying accumulated MTAs identified in the Atta (2013) genetic association study were assessed for yield. However, when only those MTAs consistent between the Atta (2013) analysis and the 2014 and 2015 head-to-head comparisons were selected an improvement in grain yield was observed. In addition, several new MTAs for yield and associated traits were identified in the head-to-head comparisons; however these must be validated in before they are used to develop new germplasm.