Root Trait Variation of Aegilops tauschii Accessions for Potential Improvement of Drought Tolerance in Winter Wheat.

Winter wheat (Triticum aestivum L.) is frequently grown under rainfed conditions and is thus particularly susceptible to yield reduction due to drought. Aegilops tauschii is the D genome progenitor of modern hexaploid wheat and is a potential source of genetic diversity for desirable root traits and other factors that may improve wheat performance under drought. The objective of this research is to characterize phenotypic variation among a diverse set of Ae. tauschii accessions for root traits related to drought responses.  Fifteen  Ae. tauschii accessions from six countries were phenotyped under fully irrigated and water-limited treatments. The greenhouse experiment was conducted using 1 m deep, 10 cm diameter tubes containing calcined clay rooting medium. All accessions entered into the experiment were grown for seven weeks with full irrigation for establishment, after which the water stress treatment was imposed for two weeks. Roots were harvested, dyed, scanned, and analyzed using WinRhizo software. There were significant differences for most measured traits among entries and between moisture treatments. On the whole-plant level, there were significant differences in root to shoot ratios among entries but the ratios were not statistically different between treatments. There was significant variation among entries and between treatments for specific root surface area. Although some entries maintained specific root surface area, root system architectures were different between the treatments. The majority of the fine root surface area was located in the top 33 cm of the root zone in the fully irrigated treatment and in the bottom 33 cm in the water-limited treatment. Additionally, entries in the water-limited treatment had a greater surface area of large diameter roots deeper in the soil profile.