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Population Structure of Potebniamyces pyri in the U.S. Pacific Northwest and Evidence of Outcrossing Inferred with Sequence-Characterized Amplified Region Markers

May 2009 , Volume 99 , Number  5
Pages  532 - 539

Q. Liu, T. L. Peever, and C. L. Xiao

First and third authors: Department of Plant Pathology, Washington State University, Tree Fruit Research and Extension Center, 1100 North Western Avenue, Wenatchee 98801; and second author: Department of Plant Pathology, Washington State University, Pullman 99164-6430.

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Accepted for publication 8 January 2009.

Potebniamyces pyri is the cause of Phacidiopycnis rot of d'Anjou pear, which is grown primarily in Washington and Oregon. To estimate the population structure of P. pyri, 146 single-spore isolates were sampled from five major pear-production areas and scored for variation at eight sequence-characterized amplified region (SCAR) loci. Significant genetic differentiation was detected among five subpopulations and a total of 54 multilocus genotypes were identified, with significant genotypic diversity in each subpopulation. No genotype was shared among more than three subpopulations. To estimate the relationship between phenotype and multilocus SCAR genotype, four to five representative isolates of each dominant SCAR genotype in each subpopulation were assayed for growth rate on oatmeal agar and virulence on d'Anjou pear fruit. Significant differences in daily growth rates and virulence were detected among genotypes; however, genotype was not predictive of virulence. To assess the mating system of the pathogen, 10 ascospores were sampled from each of 20 apothecia from a commercial orchard and scored for five SCAR markers. Segregation of alleles at one or more SCAR loci was detected among 18 of 20 ascospore progeny sets, indicating that P. pyri is likely a heterothallic fungus with a predominantly outcrossing mating system.

Additional keywords:Phacidiopycnis piri, postharvest disease, Pyrus communis.

© 2009 The American Phytopathological Society