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United States Department of Agriculture

Agricultural Research Service

Research Project: GENOMICS, GERMPLASM DEVELOPMENT AND IPM OF HOP

Location: Forage Seed and Cereal Research

2010 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. Add 1 SY. Replacing 5358-21000-035-00D (5/08).


3.Progress Report
Powdery mildew and downy mildew disease continue to impact U.S. hop production, resulting in significant input costs and crop losses for producers. Due to the scope of problems to be solved, a systems approach is required that integrates genetics, plant pathology, and integrated pest management approaches to ensure the continued economic sustainability of U.S. hop production. Focused development of disease resistant hop varieties would be greatly accelerated by the identification of molecular markers that are associated with disease resistance. In support of this effort, DNA was extracted and assayed using two different types of molecular markers on plant material from mapping populations for downy mildew resistance and beta acid production. Greenhouse scoring of parents and offspring for downy mildew resistance was completed. New molecular marker technology was used to extend the USDA-ARS generated map of the hop genome developed for identifying markers for powdery mildew resistance. An additional 380 molecular markers were added to this map, extending and saturating coverage of the hop genome two-fold. We initiated sequencing the hop genomes of the two parents used for the downy mildew mapping population. We estimate this sequencing will cover approximately 0.5% of the entire hop genome and will provide an excellent backbone from which to completely sequence the genome. Individual offspring from crosses made for germplasm and cultivar development were screened for sex (male vs female), disease resistance and plant vigor during 2009 and will be harvested August 2010. In complementary efforts to develop genetic solutions to downy and powdery mildew, integrated management approaches and modeling efforts were continued. Field validation of a molecular assay and air sampling method for detecting airborne spores of downy mildew was completed. The assay detected the pathogen in air samples no later than 8 days after the appearance of trace levels of disease. Data were collected in Oregon and Washington for validation of a model for estimating incidence of powdery mildew on cones. Preliminary results show the model explained 88% of the observed variability in disease incidence. Efforts to derive a crop loss predictor were not successful, and small plot experiments with university collaborators were initiated to quantify the effect of powdery mildew on crop yield, quality, and chemical characteristics. Year 3 of a regional, multi-disciplinary study to characterize population dynamics of arthropod pests and natural enemies in hop yards in relation to the timing of sulfur applications were completed. This research identified critical periods when powdery mildew control measures are most likely to exacerbate or suppress spider mite outbreaks. Cultural practices that suppress both downy mildew and powdery mildew were identified and, if implemented, may eliminate at least one fungicide application per acre per year.


4.Accomplishments
1. Development of integrated production strategy to maintain profitability. Spider mites and powdery mildew are common pests on many crops important to U.S. agriculture, but integrating powdery mildew management with biological control of spider mites is difficult because certain powdery mildew fungicides can disrupt biological control. ARS researchers at Corvallis, Oregon and collaborating university scientists concluded a three year study that characterized the population dynamics of arthropod pests and natural enemies in hop yards in relation to the timing of powdery mildew sulfur fungicide applications. The research identified critical periods when sulfur applications are most likely to exacerbate or suppress spider mite outbreaks, and suggested sub-lethal behavioral effects are involved in sulfur-induced mite outbreaks. The research is significant because it provides producers with cost-effective strategies to enhance biological control of spider mites related to sulfur use.


Last Modified: 8/19/2014
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