Molecular Mapping of the rps1.a Recessive Gene for Resistance to Stripe Rust in BBA 2890 Barley

Authors: YAN, G - WASHINGTON STATE UNIV; Chen, Xianming

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2007
Publication Date: 5/1/2007
Citation: Yan, G.P., Chen, X. 2007. Molecular Mapping of the rps1.a Recessive Gene for Resistance to Stripe Rust in BBA 2890 Barley. Phytopathology 97:668-673.

Interpretive Summary: Stripe rust 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 variety ‘BBA 2890’ has all-stage resistance against all races of the stripe rust pathogen identified so far in the United States. The resistance in BBA 2890 is controlled by a single recessive gene. To develop a molecular map for the gene, a mapping population was developed from a cross between BBA 2890 and susceptible Steptoe. Seedlings of the parents and the mapping population were tested for resistance to three races of the pathogen under controlled greenhouse conditions. Genomic DNA was extracted from the parents and individual lines of the population. The resistance gene analog polymorphism (RGAP) technique, which was developed in our program, was used to identify molecular markers associated with the resistance gene. A genetic linkage group was constructed for the resistance gene with 13 RGAP markers and four chromosome-specific simple sequence repeat (SSR) markers. The four SSR markers mapped the gene on the long arm of barley chromosome 3H. Some of the RGAP markers were closely linked to the resistance gene and were polymorphic in most of the barley varieties tested. These results indicate that the RGAP markers are useful for incorporating the resistance gene into most of the barley varieties.

Technical Abstract: 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 identified thus far in the United States. The resistance in BBA 2890 is controlled by a single recessive gene rps1.a. To develop a molecular map for the gene, a cross was made between BBA 2890 and susceptible Steptoe, and a population of 200 F8 recombinant inbred lines (RILs) was developed through single-seed-descent. Seedlings of the parents and all F8 RILs were tested for resistance to races PSH-14, PSH-48, and PSH-54 under controlled greenhouse conditions. Genomic DNA was extracted from the parents and 150 F8 RILs. The resistance gene analog polymorphism (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 simple sequence repeat (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 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 additional tested barley genotypes when used individually, and detected polymorphism in 88% of the genotypes when used in combination. These results indicate that the RGAP markers are useful for incorporating the rps1.a gene into most of these genotypes, and may be useful to incorporate the gene into most other barley cultivars.