Development of Molecular Markers and Their Use to Deploy Valuable Genetic Variation in California Small Grains Breedin

Responsible for over 20% of the calories consumed by humans, wheat and barley were among the first crops domesticated by humans. These two crops made a significant contribution to the transition of humans from a nomadic to an agrarian lifestyle, allowing for the development of more complex societies. After millennia of gradual farmer based selection, the green revolution of the mid-20th century dramatically increased yields of wheat at a time when the rapid human population growth threatened global food security. These rapid gains in yield resulted from the application of an improved understanding of plant genetics and a more rigorous approach to plant breeding aimed at the development of cultivars that could utilize additional nutrient inputs. The incorporation of modern molecular genetics and genomics tools to breeding has the potential to once again accelerate current rates of improvement to achieve the grain yield levels required to feed an increasing human population. This dissertation presents examples of the use of these modern tools to develop improved barley and wheat germplasm. The first chapter describes the genetic mapping of four loci for tolerance to Cereal Yellow Dwarf Virus (CYDV) tolerance in barley, a problem that has delayed the development of malting barley varieties for California. Molecular markers for these resistance genes are particularly useful because the sporadic nature of this disease poses a challenge for traditional breeding strategies. The second chapter describes the utilization of these markers for CYDV tolerance in combination with agronomic and quality tests that support the release of the two-row malting barley variety 'UC Tahoe'. The third chapter describes the validation of a novel stripe rust resistance locus in wheat, designated as Yr78. Using bi-parental population, this study identified 10 wheat accessions carrying Yr78 and a closely linked molecular marker that will be useful to incorporate this novel resistance gene in wheat breeding programs.