Location: Forage Seed and Cereal Research2009 Annual Report
1a. Objectives (from AD-416)
Identify and map molecular markers and/or genes that control the expression of specific economically important traits. Determine the loci and/or closely linked molecular markers associated with plant resistance to downy mildew using QTL analysis. Determine the loci and/or molecular markers associated with the production of beta acids in hop lupulin glands. Identify loci and/or molecular markers associated with short internode trait in hop. Develop germplasm with improved agronomic characteristics and brewing quality with combined resistance to two fungal pathogens using traditional breeding procedures. Develop predictive models for hop downy mildew and powdery mildew linked to management thresholds as components of a systems approach to pest management. Derive and validate algorithms relating weather and inoculum parameters to appearance of and infection risk by Pseudoperonospora humuli. Develop and validate PCR assays and DNA extraction protocols to monitor and detect airborne inoculum of Pseudoperonospora humuli. Develop a predictive model to estimate incidence of powdery mildew in cones and identify management threshold based on economic functions of crop loss and incorrect management decisions. Identify and develop integrated production strategies optimizing the control of both powdery mildew and biological control of arthropod pests.
1b. Approach (from AD-416)
Development and implementation of systems approaches incorporating genetic and IPM methods to reduce production costs and labor inputs. This project uses a systems approach including hop germplasm improvement for production, brewing characteristics and disease resistance through an understanding of genomics, epidemiology, and genetic mechanisms contributing to resistance to downy mildew (Pseudoperonospora humuli) and powdery mildew (Podosphaera macularis).Conventional and molecular breeding techniques will be used, PCR methodologies, GC/MS spectrophotometric, and HPLC techniques. Germplasm will be released for public use. IPM approaches will simultaneously be developed to control these diseases on cultivars with contrasting levels of genetic resistance. Previous Projects: 5358-21000-019-00D (Exp 4/01). Replacement for 5358-21000-030-00D (Exp 03/04). FY04 Program Increase $201,306. Add 1 SY. Replacing 5358-21000-035-00D (5/08).
3. Progress Report
Research progress was made on understanding the genetics of disease resistance and susceptibility, improving genetic resources for the U.S. hop industry, and developing practical tools for optimizing pest control measures and minimizing crop loss. In the genetic studies, two plant populations were increased and established in replicated field plots in Oregon and Washington in support of studies to identify molecular markers linked to resistance to the critical disease, hop downy mildew. A separate plant population also was transplanted into field plots and individual genotypes increased in a greenhouse for use in genetic studies to identify genes associated with dwarf stature in hop. Mapping of the hop genome for chromosomal regions linked to powdery mildew resistance was completed. We identified three chromosomal regions tightly linked with plant resistance to powdery mildew in one population and four chromosomal regions tightly linked to resistance in the other population. An international collaboration for a new molecular technology finished evaluating molecular markers associated with resistance to powdery mildew. In order to develop germplasm with high tolerance to powdery mildew and downy mildew, extensive disease screening and selection of seedlings was done in a greenhouse. The resulting population of 750 seedlings with tolerance to both diseases was established in a field plot in Washington State for further evaluation. Additionally, a molecular screening technique for the emerging pathogen Hop stunt viroid was adopted and is now used for screening valuable hop germplasm. To develop means to better assess infection risk associated with downy mildew, bioassay plants were deployed in a hop yard and infection risk models were developed based on weather factors. The results indicate that use of these models is most suitable during particular times of crop development, and suggest means for growers to reduce disease management costs. A simple temperature-driven model also was developed for prediction of the first appearance of downy mildew in commercial hop yards. A molecular assay specific to the downy mildew pathogen also was developed and field validation of an air sampling procedure was conducted successfully. Parallel studies with another pathogen, Sclerotinia sclerotiorum are underway with international collaborators. Data set collection is ongoing in commercial hop yards to identify factors associated with development of powdery mildew on cones for evaluation for a preliminary cone infection model. Field studies to identify the population dynamics of arthropod pests and natural enemies in hop yards in relation to the timing of fungicide usage were continued.
1. Prediction of hop downy mildew with optimized economic thresholds. Optimized and judicious use of chemical control measures is critical for enhancing the environmental and economic sustainability of U.S. agriculture. ARS scientists in Corvallis, OR and university scientists developed and evaluated infection risk models for the critical disease, hop downy mildew, and quantified economic costs associated with disease control measures and crop loss due to model predictions. Optimal management thresholds that minimize average long-term disease management costs were identified. This research is significant because it provides producers with key information on when disease forecasting is cost effective and can be used to minimize average management costs for hop downy mildew in the Pacific Northwestern U.S.
2. Genetic regions that control powdery mildew resistance in Hop. One of the major challenges hop breeders face is the lengthy evaluation period required for selecting superior lines. ARS scientists at Corvallis, Oregon, discovered three genomic regions that control expression of powdery mildew resistance in one source of resistance. ARS scientists also discovered four regions tightly linked to a different source of powdery mildew resistance in a second population. This information will help accelerate breeding programs through marker-assisted selection which is particularly important for selecting traits that are difficult to evaluate (e.g. disease resistance under variable environments) and/or require significant time or space for evaluation (e.g. low-trellis “dwarf” hop germplasm).
Mahaffee, W.F., Pethybridge, S., Gent, D.H. 2009. Injuries caused by environmental factors. In: Mahaffee, W.F., Pethybridge, S.J., and Gent, D.H. editors. Compendium of Hop Diseases and Pests. St. Paul, MN: APS Press. p.77-78.