Extensive research has been devoted to evaluating potential genotype-environment interactions. However, plant breeders are still in need of a simple way to describe how genotypes respond to different locations and years. In an environmentally diverse state like Oregon, significant genotype-environment interactions do occur The resulting lack of association between actual and genotypic potential yield performance makes it difficult to select genotypically superior lines. This study was prompted to evaluate the extent of such an interaction and compare various yield stability models. A significant genotype-environment interaction encompassing lines, environments, and years was discovered for each individual year analyzed and for the combined analysis of 1992, 1994 and 1995, and 1989 through 1994. Most lines evaluated during 1992, 1994 and 1995 were adapted to low yielding environments. However, two genotypes (OR880172 and OR880525) exhibited broad adaptation. Stephens and Mac Vicar were less adapted to the relatively high yielding Chambers site than the other genotypes tested during 1992, 1994 and 1995 due to Septoria tritici infections. The most stable genotypes during the combined 1992, 1994 and 1995 and 1989-1994 seasons were OR870831, Madsen and OR8500933H. Gene was the most desirable genotype based on stability and yield for both the combined 1992, 1994 and 1995 and 1989-1994 seasons. Due to an inability to adapt to higher yielding environments, the cultivar Rohde was the least stable genotype during the same combined periods. High and low temperatures and precipitation had minor yet significant effects on yield responses at all three sites during various periods identified. Advanced winter wheat selections and cultivars were grown in three diverse environments and compared over different time periods. Due to trial design and the objective of identifying superior genotypes from a set tested in target environments a combination of two methods, stability variance and a selection index, emerged as the most appropriate techniques. These approaches are considered the most appropriate because they use the mean of the trial as a gauge for measuring stability. / Graduation date: 1997

Wheat production in the Pacific Northwest consists mainly of the soft white wheat market class. Over 80% of this wheat is exported. In recent years there has been an increase in soft white wheat production (due in a large part to improvements in the yielding capabilities of the genotypes grown in the Pacific Northwest). To expand into different commodity markets, it would be desirable to diversify and produce wheat cultivars representing more market classes and product uses. One opportunity would be to develop cultivars representing the Hard Red Winter market class. An effort to breed high yielding, high protein Hard Red Winter wheats is now underway at Oregon State University. This research was conducted to gain a better understanding of the components (genetic and/or environmental) that determine yield and grain protein content of hard red wheat genotypes. There were two general objectives of the research. One was to study the differences in nitrogen assimilation and remobilization in a diverse group of winter wheat genotypes grown in the different agricultural environments of Oregon. The second objective was to determine the efficacy of using "hill plots" (micro-plots) as a planting method to screen for agronomic and nitrogen assimilation traits in geneticly distinct genotypes which may be used as parents in breeding efforts. Results of this study indicate that genetic differences for nitrogen assimilation and remobilization do exist, and improvements in Pacific Northwest hard red wheat genotypes can be made with appropriate selection techniques. Data also indicate that the traditional high protein wheat genotypes (from the U.S. Great Plains) do not show an advantage from a grain protein concentration standpoint when produced in the Pacific Northwest. Additionally, the environment played a critical role in determining expression of harvest index, grain protein concentration, and nitrogen harvest index. Genotype by environment interactions were high, suggesting that zone-specific varieties may need to be developed in order to attain both high grain yields and high grain protein yields. / Graduation date: 1992