Molecular mapping of the rps1.a recessive gene for resistance to stripe rust in BBA 2890 barley

Stripe rust, caused by Puccinia striiformis f. sp. hordei, is one of the most important diseases of barley in the south-central and western United States. Growing resistant cultivars is the best approach for controlling the disease. The barley genotype BBA 2890 has all-stage resistance against all races of P. striiformis f. sp. hordei (PSH) identified thus far in the United States. The resistance in BBA 2890 is controlled by a single recessive gene, rps1.a. The objectives of this study were to identify resistance gene analog polymorphism (RGAP) markers for the all-stage resistance gene rps1.a, to map the gene on a barley chromosome using chromosome-specific simple sequence repeat (SSR) markers, and to determine the presence or absence of the flanking RGAP markers for the gene in 24 barley genotypes. Seedlings of the parents and 200 F-8 recombinant inbred lines (RILs) were tested for resistance to pathogen races PSH-14, PSH-48. and PSH-54 in the greenhouse in 2005. Genomic DNA was extracted from the parents and 150 F8 RILs. The RGAP technique was used to identify molecular markers for the rps1.a gene. Twelve primer pairs generating repeatable polymorphic bands were selected for genotyping the 150 F8 RILs. A genetic linkage group was constructed for the resistance gene with 13 RGAP markers and four chromosome-specific SSR markers. The four SSR markers mapped the gene on the long arm of barley chromosome 3H. The closest RGAP marker for the resistant allele was within a genetic distance of 2.1 centimorgans (cM). The closest marker for the susceptible allele was 6.8 cM away from the locus. The two closest RGAP markers for the resistant allele detected polymorphisms in 67 and 71% of the 24 barley genotypes when used individually, and detected polymorphism in 88% of the genotypes when used in combination. This information should be useful in incorporating the resistance gene into barley cultivars and in pyramiding the gene with other resistance genes for superior stripe rust resistance.