Identification and Mapping of Quantitative Trait Loci Associated with Stripe Rust Resistance in Spring Club Wheat Cultivar JD.

Puccinia striiformis Westend. f. sp. tritici, commonly known as stripe rust, is an economically important pathogen of wheat (Triticum aestivum L.). The hexaploid club spring wheat cultivar JD contains both all-stage and adult plant resistance (APR) genes and exhibited consistent high resistance to stripe rust in the field. In this study, we aimed to identify the quantitative trait loci (QTL) for stripe rust resistance using a BC1F7 back-cross inbred-line population derived from the cross of JD and the recurrent parental line 'Avocet'. The population was phenotyped in field plots in Washington State at the Spillman Agronomy Farm in Pullman and Mount Vernon Northwest Washington Research and Extension Center in between 2014 and 2016. A major QTL tentatively designated as QYrJD.wsu-1B, conferring all-stage resistance in JD background, was identified and mapped at the telomere region on the short arm of chromosome 1B using the genotyping-by-sequencing method. This QTL was further characterized with simple sequence repeat (SSR) markers and found to have the greatest logarithm-of-the-odds score and phenotypic effect, using SSR marker wmc798 on chromosome 1BS. Seven additional QTLs associated with APR were identified in the JD background on chromosomes 2D, 3A, 3B, 4A, 6B, and 7A with partial phenotypic effects.

Characterizing and Validating Stripe Rust Resistance Loci in US Pacific Northwest Winter Wheat Accessions (Triticum aestivum L.) by Genome-wide Association and Linkage Mapping.

Stripe rust resistance is a critical need for wheat cultivars in the US Pacific Northwest (PNW). Our previous genome-wide association study (GWAS) for stripe rust resistance in a set of PNW winter wheat accessions (Panel-2) identified multiple marker-trait associations (MTAs) for both all-stage and field resistance. In this study, we conducted additional GWAS using a different set of PNW winter wheat accessions (Panel-1) that contained recently bred soft white winter wheat breeding lines and cultivars. A total of 12 all-stage resistance MTAs and eight field resistance MTAs were identified. Within these MTAs, nine MTAs for all-stage resistance and two MTAs for field resistance were located distinctly from previously characterized genes and likely represent novel loci. Markers IWB60567 (1B), IWB24342 (2A), and IWB46564 (2B) explained the largest phenotypic variances for disease responses. The analysis confirmed that MTAs on chromosome 1B were indeed the same as identified in Panel-2 and that MTAs on chromosome 2A were likely and closely linked to another field resistance QTL, (Panel-2). Haplotypes for MTAs on chromosome 1B, , and linked loci on chromosome 2A provide useful information for marker development and introgression of these QTL into wheat breeding programs.

Mapping stripe rust resistance in a BrundageXCoda winter wheat recombinant inbred line population.

A recombinant inbred line (RIL) mapping population developed from a cross between winter wheat (Triticum aestivum L.) cultivars Coda and Brundage was evaluated for reaction to stripe rust (caused by Puccinia striiformis f. sp. tritici). Two hundred and sixty eight RIL from the population were evaluated in replicated field trials in a total of nine site-year locations in the U.S. Pacific Northwest. Seedling reaction to stripe rust races PST-100, PST-114 and PST-127 was also examined. A linkage map consisting of 2,391 polymorphic DNA markers was developed covering all chromosomes of wheat with the exception of 1D. Two QTL on chromosome 1B were associated with adult plant and seedling reaction and were the most significant QTL detected. Together these QTL reduced adult plant infection type from a score of seven to a score of two reduced disease severity by an average of 25% and provided protection against race PST-100, PST-114 and PST-127 in the seedling stage. The location of these QTL and the race specificity provided by them suggest that observed effects at this locus are due to a complementation of the previously known but defeated resistances of the cultivar Tres combining with that of Madsen (the two parent cultivars of Coda). Two additional QTL on chromosome 3B and one on 5B were associated with adult plant reaction only, and a single QTL on chromosome 5D was associated with seedling reaction to PST-114. Coda has been resistant to stripe rust since its release in 2000, indicating that combining multiple resistance genes for stripe rust provides durable resistance, especially when all-stage resistance genes are combined in a fashion to maximize the number of races they protect against. Identified molecular markers will allow for an efficient transfer of these genes into other cultivars, thereby continuing to provide excellent resistance to stripe rust.