IMPROVING STEM RUST RESISTANCE AND MALT QUALITY IN THE WASHINGTON STATE UNIVERSITY BARLEY BREEDING PROGRAM
Creators: name: Brooke, Matthew James
Publisher: name: Washington State University
Year: 2024
Subjects: Barley
GWAS
High resolution mapping
Malt Qualtiy
Rpg7
stem rust

description: In 2019, a population of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici, Pgt) was collected from barley in eastern Washington. It was observed that 99% of the 100 isolates collected from the Pacific Northwest (PNW) were virulent on the cultivar Morex, which contains the resistance gene Rpg1. Furthermore, 10% of the isolates were virulent on Q21861, which contains both resistance genes Rpg1 and rpg4/5. When stacked together, Rpg1 and rpg4/5 provided exceptional resistance to all known races and isolates of Pgt collected from around the globe, including the African Pgt race TTKSK (AKA Ug99) and its lineage. Thus, this remarkable virulence is the first documentation of Pgt virulence on the Rpg1 and Rpg4/5 gene combination worldwide. This research aims to identify novel sources of seedling resistance against the virulent PNW population of Pgt. Screening of 487 accessions from the World Barley Core Collection (WBCC), representing global genetic diversity, was conducted to identify novel seedling resistance sources. A malt barley cultivar, Elliot (PI 592661), was identified to have seedling resistance to the most virulent PNW isolate, Lsp21. A biparental recombinant inbred line mapping population was developed between Elliot (resistant) and Palmer (susceptible). Utilizing QTL analysis resistance contributed by Elliot was identified as two significant QTL on chromosomes 4H and 5H. A second comprehensive screen was done on the Wild Barley Diversity Collection (WBDC). Furthermore, the WBDC was utilized using GWAS to identify 12 novel loci on chromosomes 1H, 2H, 3H, 5H, 6H, and 7H associated with resistance to Pgt isolate Lsp21. Two lines (WBDC-94 and WBDC-238) were identified to have high levels of resistance against Pgt isolate Lsp21. Both lines contain the R-gene Rpg7. Here, we genetically characterize, fine-map, and identify Rpg7 candidate genes utilizing a Morex × WBDC-94 biparental population. We successfully used high-resolution mapping to delimit Rpg7 to a 51 kb region containing two candidate genes on chromosome 3H. We hypothesize that both candidate genes, a RIN4-like protein and a RPM1-like protein, are required for resistance. The resistances are currently being integrated into elite malting barley backgrounds to enhance resistance to the virulent PNW Pgt population. Lastly, a diverse panel of 550 experimental malt lines from the WSU malt barley breeding program were used for association mapping to identify loci contributing to malt quality. A total of 44 marker trait associations were identified representing loci across all seven barley chromosomes. These markers will be used for marker-assisted selection to improve malt quality in the WSU breeding program. These quality traits will lead to the expedited development of American Malting Barley Association (AMBA) recommended varieties that can open new markets for WSU malt barley varieties. By developing malt barley varieties that have higher yields than current feed barley varieties, have resistance to stem rust, and AMBA quality standards, growers will have more incentive to grow barley due to increased profit margins.