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INVESTIGATOR: Weldon, W.

PERFORMING INSTITUTION:
N Y AGRICULTURAL EXPT STATION
GENEVA, NEW YORK 14456

ANALYSIS OF PATHOGEN DISTRIBUTION AND VIRULENCE PATTERNS AT A CONTINENTAL SCALE FOR IMPROVED MANAGEMENT OF HOP POWDERY MILDEW

NON-TECHNICAL SUMMARY: Hop powdery mildew is a major fungal pathogen of hop, directly reducing yield through damage to hop cones and reduction in alpha acid content. During the late nineteenth and early twentieth century, hop powdery mildew was a common disease problem for hop growers of the Eastern US. When the hop industry returned upon the ending of Prohibition, the Pacific Northwest (PNW) emerged as the primary hop production region in the US. The region now produces well over 95% of the US hop supply. In 1997 Podosphaera macularis, the causal organism of hop powdery mildew, was first confirmed in the PNW. Over 800ha of hops went unharvested that year alone due to damage caused by hop powdery mildew. As the craft brewing industry has exponentially grown over the past decade, hop production has re-emerged in both the Midwest and Eastern US to meet the demand of brewers for locally sourced hops. Hop powdery mildew has been confirmed to be present in many of the newly establish commercial yards these regions east of the Rocky Mountains. The question remains as to where this source of powdery mildew originates -- from feral hop plants that are leftovers from the twentieth century industry and exist in forests and along riverbanks, from spread between commercial yards, by arriving in on the original planting material, or a mixture of the three scenarios. Additionally, within the dense areas of hop production in the PNW, often with little variation in the hop varieties planted and a heavy reliance on fungicides for disease management, there is a huge potential to select for highly virulent strains of P. macularis. Within this region, two adapted strains have recently emerged that efficiently grow on hop varieties previously considered resistant -- 'Nugget' and 'Cascade'. It is crucial that a rapid, scalable tool be developed to track the spread of these virulent strains of the pathogen and address the additional questions regarding how hop powdery mildew is spreading to new yards. This project will meet these grower needs by developing and validating a library of molecular marker "barcodes" that can be used to survey large collections of P. macularis samples at once and return data about each sample's origin and virulence profile. This will allow hop growers to understand their specific local hop powdery mildew population and make informed decisions regarding how they choose to source their planting material, in varietal selection and in use of various fungicide chemistries.

OBJECTIVES: The primary overarching goal is to generate a validated molecular marker library to track hop powdery mildew (HPM) populations directly affecting US production. Development of this tool fulfills a long term goal of sustained and rapid tracking of hop powdery mildew populations with specific virulence profiles or geographic origins. This will advise grower management practices through targeted selection of hop varieties or fungicide chemistries most appropriate for their local hop powdery mildew population, and also provide evidence as to how hop powdery mildew populations are being introduced into previously unifencted hop yards throughout the US.Objectives Undertaken to achieve these goals:Creation of a molecular marker library based on genetic differences (SNPs) in a transcriptome dataset of a highly diverse hop powdery mildew sample collection -- markers intended to differentiate samples based on geographic origin, origin in a feral or commerical hop planting, and by specific virulence traits such as R6 virulence.Heirachical sampling of hop powdery mildew: 7 samples per hop location, both feral/ wild hop and commercial hop locations, multiple locations per geography (at least 5), and mulitple geographies (Pacific Northwest, Midwest, Eastern US, and Europe). Project timeline allows for two summer seasons of hop powdery mildew sample collection if needed. One summer may be enough.Genotyping of the heirachical HPM sample library using the molecular marker library and an Amplicon Suequencing (AmpSeq) approach -- validation of the molecular marker libraryMating type determination of all hop powdery mildew samplesPublication of manuscripts detailing the molecular marker library, making it available for future monitoring of hop powdery mildew populations. Publication of extension reports summarizing major findings for an extension/ grower audience. Presentation of hop powdery mildew population structure at local, regional, and national hop commodity meetings.