Mechanisms of Adaptation to Water-Stress Conditions in Widely Planted TAM Wheat Cultivars.

Hard red winter wheat cultivation in the Texas High Plains and the Southern Great Plains (SGP) of United States often experience periodic water-stress during and after head development resulting in massive yield losses.  Among the varieties released by Texas AgriLife Research and Extension Center, TAM 111 and TAM 112 have been cultivated widely in SGP and showed better adaptation to water-stress conditions with higher grain yields.  Preliminary studies suggested that both cultivars may employ different mechanisms to variable stress level nevertheless; the physiological and molecular basis of their adaptation remains unknown.  A detailed greenhouse and field experiments were conducted with the objective to elucidate the mechanisms of drought tolerance (resistance?) in TAM 111 and TAM 112 in comparison with TAM 304 (relatively less drought tolerant cultivar with high yields under irrigated conditions).  In the greenhouse (GH), three cultivars were grown under wet and dry (90 and 50 % field capacity respectively) conditions while, in field conditions, they were grown in dryland and five different irrigation levels (40, 50, 65, 75, and 100 % potential evapotranspiration [PET]).  Water use dynamics, cumulative transpiration, water use efficiency, tiller number, shoot and root biomass, yield parameters, harvest index, chlorophyll content, gas exchange, canopy temperature were measured.  The results from GH show that TAM 112 has used more water in both wet and dry conditions compared to TAM 111 and TAM 304 and resulted in more shoot and root dry weight.  Allocation of water to produce unit root and shoot dry weight was found to differ among cultivars at different growth stages suggesting diverse mechanisms of stress adaptation in potted GH experiments.  The other results also shed light on plausible mechanistic adaptations to water-stress by leading TAM cultivars and are expected to assist in new cultivar development and better management practices.