Changes in grain quality and grain protein composition of winter wheat cultivars under different levels of soil nitrogen and water stress

Hard white winter (HWW) wheat cultivars must have superior protein quality and consistent processing quality to be successful in the Asian market. New cultivars and management strategies are needed to produce HWW grain for both bread and noodle applications from diverse environments in the US Pacific Northwest (PNW). This study investigated the variability in grain quality, grain protein content and composition, and dough mixing properties in relation to moisture stress during grain-fill and nitrogen management in the PNW. Seven HWW and two soft white winter wheats were grown under line source irrigation and two nitrogen fertilization levels over two years and two locations. Plots were irrigated during grain-fill to replace from 100 to less than 30 % of measured evapotranspiration. Grain quality, protein quality, and protein composition were characterized by nitrogen determinations, single kernel analysis, polyphenol oxidase activity (PPO), SDS sedimentation tests, Mixograph analyses, and size-exclusion HPLC. Water stress during grain-fill negatively affected grain yield, test weight, and kernel weight and diameter. Among HWW cultivars, water stress caused reductions in test weight which were of larger magnitude in late maturing cultivars than in early genotypes. Mixograph peak time, stability, and tolerance were relatively unchanged over irrigation treatments. Nitrogen fertilization showed a positive contribution to both protein quantity and quality, without affecting PPO levels. Moreover, no significant correlation was found between flour protein and PPO. Changes in protein quality and composition were related to general increases in protein concentration, regardless if the result of reducing irrigation or increasing fertilization. The proportion of monomeric proteins (gliadins) increased more rapidly than the polymeric proteins (glutenins) as flour protein increased. Grouping of genotypes in biplots indicated that cultivars of similar quality responded similarly to treatment combinations in terms of protein quality and dough mixing properties. The patterns of response suggest that management strategies to meet target protein content and end-use quality are relatively independent of genotypic differences. Similar management strategies could then be recommended for HWW when targeting specific end-uses. Early maturity reduced the impact of water and heat stress during grain-fill and would contribute to enhance grain quality and consistency in PNW cultivars.