Drought Response of Winter Wheat Cultivars Grown under Field Stress Conditions 1

Ten winter wheat cultivars ( Triticum aestivum L.) were evaluated for grain yield and yield components under moisture stress conditions at three locations. Osmotic potential (Ψ n .) was determined from leaf samples taken during the early part of grain filling. Consistent genetic differences were found for Ψ n … Significant positive associations of Ψ n with yield existed at two locations (r= 0.49 and 0.45). Path‐coefficient analysis indicated that Ψ n . contributed positively to yield differences primarily by way of kernel weight at Pendleton, the least stressed site. Increased Ψ n 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 Ψ n ). At Heppner, the large direct effect on yield by spikes/m 2 negated the small positive indirect effects of Ψ n 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 Ψ n decreased over time (‐ 17.1 to ‐ 31.8 bars). Cultivar Ψ n 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.