Traits for Drought Tolerance in Wheat: Phenotyping, Genetics and Genomics

Wheat production faces intermittent, sporadic and sometimes chronic drought conditions. The uncertainty of sufficient moisture availability necessitates development of wheat varieties that yield well under normal conditions and also produce economically viable crops under drought. Drought tolerance is a complex conglomeration of various molecular, biochemical, developmental and physiological phenomena. Teasing these apart and re-building desirable combinations in adapted germplasm requires investigations of the genetic factors under controlled drought conditions and validations in target environments. Our work on phenotyping, genetics and genomics is confined to adapted germplasm for which bi-parental mapping populations are available. The objective is to identify drought-related traits in this germplasm and to investigate the genetic underpinnings of prioritized traits. We have standardized an experimental design for evaluating whole phenology under controlled drought conditions. This phenotyping system allows for root depth up to 120 cm and for retrieval of roots for further analyses, and interesting root phenotypes have been noted in this platform. Selected Triticum turgidum ssp durum varieties (Strongfield; Commander; Pelissier) and T. aestivum (Cadillac; Carberry) were evaluated for above-ground biomass, height, tillers, spike characteristics, grain numbers, grain weight, harvest index, root biomass, photosynthesis parameters, water relations and water use efficiency (WUE) in this system. Pelissier showed higher root biomass than Strongfield, and Commander also had more root biomass than Strongfield. AC Cadillac was better in this regard than Carberry under drought stress. Pelissier showed higher WUE than the other two durum varieties, indicating stress adaptation toward conserving water. Unlike the other wheat lines, Pelissier did not show a statistically significant reduction in per-plant yield under drought. Field trials of the hexaploid mapping population and that of Strongfield x Commander and Strongfield x Pelissier that are in progress offer opportunities for comparing phenotypes under different conditions. Commander, a semi-dwarf with Rht-B1b allele, did not suffer reduction in height under stress but other wheat lines did, as also observed under field conditions. Mapping the Strongfield x Pelissier population is in progress, and mRNA-Seq analysis has revealed gene expression differences in the source and sink tissues of plants under stress.