Drought Response of Winter Wheat Cultivars Grown under Field Stress Conditions

Ten winter wheat cultivars (Triticum aestivum L.) were evaluated for grain yield and yield components under moisture stress conditions at three locations. Osmotic potential (Ψₙ.) was determined from leaf samples taken during the early part of grain filling. Consistent genetic differences were found for Ψₙ... Significant positive associations of Ψₙ with yield existed at two locations (r= 0.49 and 0.45). Path-coefficient analysis indicated that Ψₙ. contributed positively to yield differences primarily by way of kernel weight at Pendleton, the least stressed site. Increased Ψₙ made contributions to high yield via spikelets/spike, kernels/spikelet, and kernel weight at Pilot Rock, a severely stressed site. High spike numbers had a tendency to be associated with low plant water status (low Ψₙ). At Heppner, the large direct effect on yield by spikes/m² negated the small positive indirect effects of Ψₙ via the later-developed yield components. In a growth analysis study at Pilot Rock, five cultivars were sampled over four time intervals from spike initiation to ripe stage. The mean Ψₙ decreased over time (- 17.1 to - 31.8 bars). Cultivar Ψₙ values ranked consistently and differences became larger after the onset of high soil moisture stress (< - 15 bars). The drought-resistant cultivar ‘Yamhill’ avoided drought stress by maintaining a high plant water status during reproductive development. The high growth rates during heading and anthesis and a high kernel weight indicated that this cultivar was less affected by high external water stress. The drought-resistant cultivar ‘Wanser’ tolerated a high internal stress by maintaining a large number of tillers through development to harvest. Characterization of other cultivars also indicated that both avoidance and tolerance traits contributed to grain yield under drought stress.