X.M. Chen, M.N. Wang, A.M. Wan, K.C. Evans, Y.M. Liu, M. Heath, J. Feng, and Y. Zhou USDA-ARS Wheat Genetics, Quality, Physiology, and Disease Research Unit and Department of Plant Pathology, Washington State University
ABSTRACT: In 2014, the low level of stripe rust was accurately forecasted using prediction models. Rust updates and advises were provided on time to growers for implementing appropriate disease management based on the forecasts and field surveys, which prevented unnecessary use of fungicides and saved growers millions of dollars. Wheat stripe rust occurred at the Pacific Northwest (PNW) at the lowest level in the past 15 years and also at low levels in other regions in the U.S. Barley stripe rust was also very low. Wheat leaf rust occurred in western Washington, but not found in eastern Washington. Barley leaf rust was severe in western Washington, but was not found in eastern Washington. Stem rust of wheat and barley was not observed in Washington. From 319 stripe rust samples collected from wheat (288), barley (24), triticale (1), rye (1), and grasses (5) in 13 states, we identified 33 races of the wheat stripe rust pathogen, 5 races of the barley stripe rust pathogen, and determined their distributions and frequencies in the country and various stripe rust epidemiological regions. Five of the wheat stripe rust pathogen races were new. Using virulence and molecular marker data, we determined that the stripe rust pathogen population in the western U.S. is more diverse than the population in the eastern U.S. We determined the bases for the fact that barberry plays essential role for stem rust, but not for stripe rust. Because the natural infection of the stripe rust pathogen was low, in 2014 we inoculated the experimental nurseries around Pullman with races which were predominant in the region in 2013, and created adequate disease levels for screening wheat and barley germplasm. We evaluated more than 30,000 wheat and barley entries for resistance to stripe rust. Using the stripe rust data, we collaborated with breeders in releasing five wheat varieties (WA 8162, WA 8165, WA 8166, WA 8169, and WA 8184) and one barley (2004NZ151) variety and registered seven wheat varieties and one barley variety. In 2014, we published the research results of mapping stripe rust resistance genes Yr59, Yr62, Yr64, and Yr65 in wheat germplasm; mapped two genes for effective all-stage resistance in wheat genotype PI 195097 and two genes for high-temperature adult-plant resistance in wheat genotype PI 182126; and developed 15 mapping populations for identifying more resistance genes in wheat germplasm. We tested 30 fungicide treatments in fields for control of stripe rust; and 24 winter and 16 spring wheat varieties for their yield loss and fungicide response. The results of our fungicide tests and yield loss tests of currently grown PNW varieties are used for guiding rust management.