Location: Forage Seed and Cereal Research
Project Number: 5358-21000-046-00
Start Date: Jun 16, 2013
End Date: Jun 15, 2018
Objective 1: Identify molecular markers associated with plant resistance to P. humuli and P. macularis. Progeny developed from crosses of resistant and susceptible parents will be screened by pathogen challenge, and single nucleotide polymorphic (SNP) marker identification and genotyping-by-sequencing will be performed. Objective 2: Development of multiple pathogen resistant germplasm or varieties. Progeny of crosses of parental material that possess relative resistance to powdery and downy mildews will be successively challenged with each disease to identify germplasm with enhanced resistance to both. Resistant germplasm that possess excellent agronomic and brewing characteristics will be released. Objective 3: Construct optimized integrated management approaches for powdery mildew susceptible cultivars. Hypothesis 3.A: Successful perennation of the powdery mildew fungus occurs via infection of juvenile crown buds and such crown buds develop asynchronously. Management factors that reduce late season severity of powdery mildew will reduce overwintering survival of the pathogen. Crown bud development phenology will be determined and plants will be challenged with powdery mildew at selected stages. Treatment at different stages will be evaluated. Hypothesis 3.B: The absence of the ascigerious stage of Podosphaera macularis in the Pacific Northwestern U.S. is due to the absence of one of requisite mating types of the fungus. PCR amplification of conserved regions in MAT1-1 and MAT1-2 loci of P. macularis will be optimized and pathogen isolates collected from a variety of cultivars and hop yards in the Pacific Northwest will be tested to determine the frequency of each mating type. Objective 4: Develop and apply genotyping approaches. Hypothesis 4.A: P. humuli is heterothallic, possessing a high degree of genetic diversity in the Pacific Northwestern U.S, and the population is structured at the scale of individual fields. P. humuli isolates will be obtained from three hop yards in western Oregon. After suitable SSR loci and primers are developed from pyrosequences, genotyping will be performed by capillary sequencing of 7 to 10 SSR loci per isolate. Hypothesis 4.B: The population of Podosphaera macularis in the Pacific Northwestern U.S. exhibits a low degree of genetic diversity or structure based on geography or cultivar host. Multiple nuclear loci will be identified, PCR-amplified, and sequenced from Pacific Northwest, northeastern U.S., and European isolates. Population genetic parameters will be calculated and differentiation among geographic populations will be estimated.