Yield variation, plasticity, adaptation, and performance ranking of winter wheat varieties across the environmental gradient of the US Pacific Northwest

The US Pacific Northwest is a major wheat (Triticum aestivum L.) production region with widely ranging water availability across its dryland and irrigated cropping systems. There have been no evaluations of variation, plasticity, adaptation, and performance of wheat yield due to variety-collectively or individually-that consider the entire environmental gradient of the region, useful for yield gap analysis, informing breeding, and other applications. Our objectives were to provide these evaluations using a large variety trial dataset and an independent dataset. Using linear models covering site-averaged yields (x variable) from about 1.50 to 12.0 Mg ha-1, upper and lower yield boundaries due to differences in variety performance were characterized by the regression models y = 1.08x + 0.24 and y = 0.906x - 0.13, respectively. The accuracy and usefulness of these functions were validated by the close fit of an independent dataset. Yield plasticity and environmental adaptation of 45 individual wheat varieties were also evaluated using the Finlay-Wilkinson regression approach, which showed wide variation in varietal yield responses to environment and substantial differences in yield stability (i.e., variation around the yield trend). A limitation of this analytical approach has been that the regression coefficients are not directly useful for ranking varieties for yield performance across contrasting environments. A simple transformation procedure of the coefficients into a single metric was effective for rapidly providing such rankings. A limited analysis is presented quantifying the relative contributions of genotype (27%-58% within sites), environment (84% across sites), and their interaction (5% across sites) on regional yields, as well as yield analysis of club wheat. In summary, this work provides useful research tools and a region-wide perspective on yield traits of Pacific Northwest wheat varieties.