2009 Annual Report 1a.Objectives (from AD-416) Evaluate the reaction of advanced barley breeding lines from various public and private breeding programs to established races of barley stripe rust (Puccinia striiformis f.sp. hordei) endemic in the Central Valley of California. 1b.Approach (from AD-416) Barley breeders will submit their advanced lines to UCDavis researchers, who will plant the accessions in the Davis, California area or other Central Valley locations where a natural epidemic of barley stripe rust can be expected. Data collected will be returned to the participating breeders and ARS distribution to interested parties. Documents SCA with UC Davis. 3.Progress Report The 2008-2009 barley stripe rust screening nursery included 522 entries of 4 nurseries. The susceptible barley cultivar (Max) was used as a spreader raw and susceptible check to facilitate natural stripe rust infection. Stripe rust developed later in 2009 than in 2008 in California, with initial infections observed in the middle of March on the spreader rows at UC Davis as compared to late February in 2008. Rainfall was limited at the beginning of the season affecting the spread of the disease. Later rains and cool temperatures extended the period for stripe rust to develop, increase in severity, and ultimately generate high levels of inoculum. Generally, high level of stripe rust infection has been observed throughout the nursery that was sufficient to discriminate resistance from susceptible materials. In both wheat and barley, first infection was detected on spreader rows and highly susceptible lines. The first stripe rust infection was detected on March 3, 2009 on spreader rows of wheat. Two dates of stripe rust ratings, severity and infection types (April 20-21 and May 4-5, 2009) were taken in both nurseries. Apart from screening, twenty nine samples infected with stripe rust of California have been collected during the 2009 growing season and were submitted to the USDA rust laboratory at Pullman, WA, for race identification. Monitoring of activities in this agreement were accomplished by telephone and e-mail.