Nested Association Mapping of Water Use Efficiency in Spring Wheat (Triticum aestivum L.) Using Carbon Isotope Discrimination Analysis and Remote Sensing Traits.

Water shortage is the most significant factor limiting wheat (Triticum aestivum L.) production in the world. Therefore, the development of productive, drought tolerance cultivars is a pressing need. Wheat cultivars with higher water use efficiency (WUE) have been shown to be less susceptible to yield losses under water limited conditions.  In order to dissect and understand the genetic architecture controlling WUE in spring wheat, and to facilitate breeding for drought tolerance a genome-wide nested association study was conducted.  A 750 recombinant inbred line nested association mapping population, designed for drought, was phenotyped for carbon isotope discrimination (CID), a surrogate measure for WUE, various physiological traits using remote sensing and agronomic traits in 2014 and 2015. The entire population was genotyped with an Infinium 90K SNP array and genotyping by sequencing (GBS). Using joint inclusive composite interval mapping we identified 20 quantitative trait loci (QTL) for water use efficiency and more than 30 QTL for physiological traits associated with plant water status and health across both years.  Multiple pleiotropic QTL regions for WUE and grain yield were identified on chromosomes 1A, 1B, 4A, 4B, 6A, and 7B. Future studies exploring the genomic regions identified in this study will improve selection efficiency for drought adaptive cultivars by enabling marker-assisted selection for WUE in spring wheat.