Collaborative Breeding to Improve Stripe Rust Resistance in Wheat.

Stripe rust (caused by Puccinia striiformis f. sp. tritici) of wheat (Triticum aestivum L.) is found in all major wheat growing regions of the United States. Breeders utilize both seedling and adult plant resistance in wheat to effectively reduce yield loss caused by stripe rust in these regions.  Unfortunately, phenotyping for stripe rust resistance is limited to the Pacific Northwest where stripe rust occurs on an annual basis. The goal of this research was to screen for stripe rust resistance in winter wheat genotypes from breeding programs around the United States over three years and assess the resistance of each program. Seedling resistance was conducted in the greenhouse in 2015 and 2016 using common races pstv-37 and pstv-14, respectively. The field screens were conducted in 2014 on 366 different genotypes, in 2015 on 373 genotypes, and in 2016 on 1,218 genotypes across two locations in eastern Washington. When possible, two field ratings were taken in May and/or June for infection type (IT, 1-9) and disease severity (SEV, 0-100%). Across all three years, the average field IT and SEV were 6 and 37%, respectively. In 2016, lines from SUNWHEAT nursery had the best overall resistance whereas lines from Illinois-KWS had the least. The seedling data showed that all breeding groups fell between an average IT score of 6 and 7 when screened with pstv-14 and an IT score of 5 and 7 when screened with pstv-37. The findings from this study allows breeders to identify the strength and weakness in their genetic resistance to stripe rust. With the continuation of field and greenhouse data, breeding programs will be able to phenotype their material for resistance on an annual basis and identify resistant germplasm in their populations.