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United States Department of Agriculture

Agricultural Research Service

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Location: Physiology and Pathology of Tree Fruits Research

2011 Annual Report

1a. Objectives (from AD-416)
We have elected to initiate this integrated research and outreach activity to tackle fire blight disease and provide solutions, both short- and long-term, to this important agricultural problem using a multidisciplinary approach. Our short-term goal is to develop environmentally sound and effective methods of management and control for this disease, by capitalizing on 1) state of the art knowledge of the biology of the pathogen, host, antagonists, and inhibitors; and 2) advances in high-technology, in particular nanotechnology, for delivery of control agents. Our long-term goal is to incorporate genetic resistance into the host, apple, so that apple trees can fight off the pathogen on their own. This will capitalize on 1) expansive genomics resources available for the apple genome; and 2) genomics-based approaches for identifying and characterizing these genes. These isolated gene(s) can then be incorporated in the future into apple using established genetic engineering technologies. Throughout this project, we will translate project outcomes to beneficiaries of this research, namely growers and consumers, through effective and innovative outreach and educational programs, and we will address the economic benefits and available marketing tools to support adoption of the end products of this integrated genomics and management systems project. Objectives: 1. Evaluate and assess virulence inhibitors against Erwinia amylovora. 2. Evaluate and enhance efficacy of microbial biocontrol agents. 3. Controlled and sustained delivery of virulence inhibitors and biocontrol agents mediated by microparticles/nanoparticles. 4. Identify and clone fire blight resistance genes. 5. Develop and deliver outreach programs for comprehensive management systems for fire blight. 6. Develop and assess economic and marketing opportunities for biocontrol of fire blight disease as well as develop fire blight resistant apple varieties.

1b. Approach (from AD-416)
Since many chemical compounds have been found to be effective against a broad-range of Gram-negative mammalian pathogens, we hypothesize that compounds identified for mammalian systems will also be effective against plant enterobacteria, which share similar type III secretion systems as the main virulence mechanism to cause disease. Experiments will be designed to use known virulence inhibitors effective against mammalian pathogens to test their effectiveness against E. amylovora, both in vitro and in vivo, and to determine the potential molecular mechanisms involved in suppressing the virulence of the pathogen. The mechanisms of the commercially available biocontrol agent, P. agglomerans strain E325, and selected bacterial and yeast antagonists highly effective against E. amylovora in screening tests on blossoms, will be studied using a synthetic medium based partially on the chemistry of flower stigma exudates and using detached crab apple flowers in controlled environments. The effectiveness of strain E325 will be enhanced by altering production and formulation procedures to increase production of an antibiotic highly specific to E. amylovora and to increase the tolerance of E325 to desiccation on flower surfaces. Efficacy of biological control will also be increased by combining E325 with other antagonists with complementary mechanisms and ecological niches. Highly effective antagonist mixtures, virulence inhibitors, or combinations of these agents will be field tested at Wenatchee (WA), Urbana (IL), and East Lansing (MI). Biodegradable and biocompatible materials will be developed for the sustained delivery of virulence inhibitors and biocontrol agents in orchard environments. This will be mediated by microparticles or nanoparticles with optimized size and architecture to facilitate controlled release of the control agents over time. Based on previous studies by various groups identifying QTL for fire blight resistance, the QTL identified from both the crab apple ‘Everest’ and M. floribunda 821 and located on LG12 of the apple genome will be targeted for identifying gene(s) for resistance to fire blight. Efforts will be made to identify a BAC contig on the apple physical map covering the QTL for fire blight resistance and fine mapping of the QTL region. Following sequencing of the BAC contig, candidate genes will be identified. The function of the genes will be analyzed by transforming plants, through overexpression and knockouts, and transformed plants will be evaluated for fire blight resistance in a greenhouse. New technologies for fire blight management will be delivered to the tree fruit industry through the development of a project website and educational programs covering biocontrol, nanotechnology, and genomics.

3. Progress Report
This report relates to objective 1 of the associated in-house project, which seeks to improve fire blight management through advancements in the production and formulation of microbial biocontrol agents used to suppress the disease organism on flowers of apple and pear trees. This project was funded by a grant from USDA-NIFA, Specialty Crop Research Initiative. The Project Director (PD) is located at the University of Illinois (UI), Department of Natural Resources and Environmental Sciences, Urbana. The project component on biological control is being led by ARS at Wenatchee, WA. Additional details of the research can be found in the report for the in-house associated project, 5350-22000-015-00D, Biological Integrated Management of Fire Bight of Pome Fruits. The PD and Co-Principal Investigators (Co-PIs) on the project interacted through teleconferences and email during the past year. The Co-PI at Wenatchee met with the PD and Co-PIs at UI in December of 2011 to discuss research results obtained so far and plan new strategies for going forward. In addition to work described in the in-house project, personnel at Wenatchee have supported the efforts of a plant pathologist at UI, Dept. of Crop Sciences, to evaluate small molecule virulence inhibitors as novel antibacterial agents, some of which are natural products, to essentially disable the fire blight organism and prevent it from causing disease. So far, information and materials, specifically immature pear fruit for laboratory assays, has been provided. The group at Wenatchee is also cooperating with two engineers at UI, Dept. of Electrical and Computer Engineering and Center for Nanoscale Science and Technology, to develop microcapsules suitable for delivering biocontrol agents for fire blight. The objective is to protect biocontrol agents during application and initial establishment on the surfaces of flowers from environmental factors and from other materials applied in orchards, including blossom thinning agents. The Wenatchee group has provided a substantial amount of information and conceptual input related to the microecology of floral surfaces and the establishment of an appropriate microcapsule size and release time. One milestone reached was the encapsulation and sustained viability of a biocontrol agent on floral tissues in the laboratory. The research supports Component 4 (Biological and Cultural Strategies for Sustainable disease Management) of the NP 303 Action Plan by: (a) Developing an ecologically based strategy for the control of fire blight of apple and pear crops; (b) enhancing the efficacy of biological control agents; and (d) integrating multiple disease management tools. Progress is monitored through conference calls and oral progress reports at annual meetings of project team at University of Illinois.

4. Accomplishments

Last Modified: 07/19/2017
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