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ARS Home » Pacific West Area » Pullman, Washington » WHGQ » Research » Publications at this Location » Publication #292801
Title: Virulence and molecular analyses support asexual reproduction of Puccinia striiformis f. sp. tritici in the U.S. Pacific Northwest

Author
item CHENG, PENG - Washington State University
item Chen, Xianming

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2014
Publication Date: 11/1/2014
Citation: Cheng, P., Chen, X. 2014. Virulence and molecular analyses support asexual reproduction of Puccinia striiformis f. sp. tritici in the U.S. Pacific Northwest. Phytopathology. 104(11):1208-1220.

Interpretive Summary: Wheat stripe rust occurs every year and has caused frequent epidemics in the U.S. Pacific Northwest (PNW). Races of the stripe rust pathogen change rapidly and barberry plants, which could be alternate hosts of the fungus, are found in the region. However, whether sexual reproduction occurs in the pathogen population under natural conditions in the region is not clear. To determine the reproduction mode of the fungus, a systematic collection of single-stripe leaf samples of stripe rust was made in 26 fields in the PNW in 2010. A total of 270 isolates obtained from the PNW collection, together with 66 isolates from 20 other states collected in the same year, were characterized by virulence tests and simple sequence repeat (SSR) markers. A total of 21 races and 66 haplotypes were detected, of which 15 races and 32 haplotypes were found in the PNW. Cluster analysis with the SSR marker data revealed two genetic groups, the first group was mainly found in the PNW containing more “homozygous” (more SSR marker loci have identical alleles) isolates and the second group consisted of more “heterozygous" (More SSR marker loci have different alleels) isolates collected throughout the U.S. including the PNW. The molecular genetic groups generally corresponded to the two virulence groups. The analyses of multi-locus association, parsimony tree length permutation, and Hardy-Weinberg equilibrium ruled out the possibility of sexual reproduction in the PNW population, indicating that the fungal pathogen reproduces asexually.

Technical Abstract: Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), occurs every year and has caused frequent epidemics in the U.S. Pacific Northwest (PNW). Races of Pst change rapidly and barberry plants, which could be alternate hosts of the fungus, are found in the region. However, whether sexual reproduction occurs in the Pst population under natural conditions in the region is not clear. To determine the reproduction mode of Pst, a systematic collection of single-stripe leaf samples of Pst was made in 26 fields in the PNW in 2010. A total of 270 isolates obtained from the PNW collection, together with 66 isolates from 20 other states collected in the same year, were characterized by virulence tests and simple sequence repeat (SSR) markers. A total of 21 races and 66 haplotypes were detected, of which 15 races and 32 haplotypes were found in the PNW. Cluster analysis with the SSR marker data revealed two genetic groups, the first group was mainly found in the PNW containing more “homozygous” isolates and the second group consisted of more “heterozygous" isolates collected throughout the U.S. including the PNW. The molecular genetic groups generally corresponded to the two virulence groups. The analyses of multi-locus association, parsimony tree length permutation, and Hardy-Weinberg equilibrium ruled out the possibility of sexual reproduction in the PNW population, indicating that Pst reproduces asexually.