Root traits contributing to drought tolerance of synthetic hexaploid wheat in a greenhouse study

Drought stress imposes major limits on wheat (Triticum aestivum L.) yield and is predicted to increase in frequency due to climate change. The aim of this study was to explore the potential of synthetic hexaploid wheat (SHW) to improve productivity of winter wheat under drought stress. Six SHW lines and four winter wheat cultivars from the U.S. Great Plains were evaluated in 1 m x 10 cm plastic tubes under drought- stressed and well-watered conditions in a greenhouse study. Root morphology, biomass, stomatal attributes, plant water relations, and the response of these traits to drought stress were measured. Traits significantly (P < 0.05) correlated with a drought tolerance index included root biomass in the bottom third of the tubes, length of the longest root, stomatal conductance, and production of small diameter roots. Plasticity for root biomass allocation to greater depths showed a strong association with maintenance of plant water status. Synthetic line SYN-201 ranked highest for deep root biomass and length of the longest root under stress, and demonstrated plasticity by shifting root biomass production from the upper third to the bottom third of the tubes when stressed. Digital analysis of root morphology indicated that SYN-201, SYN-290, and cultivar Byrd produced large amounts of small diameter roots at depth. SYN-396 showed high stomatal density and reduced stomatal aperture while maintaining leaf growth when stressed despite a lack of deep roots. Trait variation in the SHW lines may contribute beneficial drought tolerance to Great Plains- adapted cultivars through introgression of novel allelic diversity.