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United States Department of Agriculture

Agricultural Research Service

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Location: Physiology and Pathology of Tree Fruits Research

2009 Annual Report

1a.Objectives (from AD-416)
The long-term objective of this project is to develop a stable, biologically relevant taxonomy for the genus Alternaria with particular reference to the small-spored members of the genus, which are the taxa most often involved in phytosanitary issues and which are also frequently misidentified. Associated with this objective is the development of molecular protocols for detection and identification of target species of phytosanitary importance that are based upon the systematics work. Certain species of Alternaria (e.g., A. gaisen, A. yaliinficiens) are currently known to have a limited geographic distribution that restricts the movement of deciduous tree fruit to the U.S. and other world markets. Other species, many of which are undescribed or frequently misidentified, occur in the United States and in other countries, and need to be characterized and described so that regulatory actions regarding Alternaria on intercepted plant products can be based upon a firm and scientific understanding of the Alternaria taxa that occur on tree fruits and other substrates in the U.S. Over the next 5 years we will focus on the following objective: Objective 1: Isolate and accumulate sequence data from genomic transcripts of known Alternaria spp. which are detected during development of phenotypic traits that vary among different sub-generic groups sensu Simmons and Roberts (1993) and species within those groups, with particular emphasis on sporulation pattern, conidial morphology and, if necessary, germination-mediated metabolite production.

1b.Approach (from AD-416)
A fundamental understanding of species-diversity (identity) among Alternaria strains associated with tree fruit will be developed using morphological characters and species-specific DNA sequences identified via subtractive hybridization protocols. Research will be conducted as necessary to address market- or issue-specific questions that arise from interactions with trading partners. Replacing 5350-22000-014-00D (11/03).

3.Progress Report
Activities for this project address Problem Statement 1B: Detection, Identification, Characterization, and Classification of Pathogens in the NP 303 Action Plan. Within this problem statement, three sub-problems most accurately describe the current and future research efforts within the project. 1. Although accurately classifying pathogens is important for understanding disease etiology, transmission, and control, the systematics of plant pathogens is plagued by large gaps in knowledge about specific groups of pathogens. 2. Because agricultural globalization has expanded, the need for taxonomic and other biological knowledge of foreign pathogens similarly has increased. 3. Because new molecular approaches may yield accurate tests only when developed within a sound systematic framework, such method development will also require complementary morphological research.

We continued to develop and modify the methods we are using to find small pieces of DNA that are specific for certain species of exotic mold pathogens and which will allow development of DNA-based tests to determine if the exotic pathogens are hitchhiking into the country on imported commodities. The exotic pathogen we worked with during the past year is Alternaria gaisen, which causes a disease called “black spot” of Japanese pear. Recent modifications have greatly increased the number and specificity of DNA pieces that are now available for testing.

1. Providing evidence to WTO for expansion of apple exports. Because fire blight disease occurs in the U.S. but not in Japan, Japan restricted the import of US apples for decades even though there was no scientific evidence to show that apple fruit could spread the disease. Although the U.S. won a WTO dispute against Japan over the issue in 2005, Australia was taken to WTO in 2009 over the same issue because it maintains similarly restrictive import regulations that prevent export of US and New Zealand apples to Australia. Because both WTO cases were based in large part upon fire blight research done at the Tree Fruit Research Lab in Wenatchee, WA, ARS scientists at Wenatchee, WA supported USDA-APHIS, counsel for the office of the U.S. Trade Representative, and New Zealand Ministry of Agriculture, Foresty and Fisheries by providing technical review and comment on both New Zealand's submissions (first, rebuttal, and answers to Panel questions submissions) and the third party submission of the U.S. The Panel is scheduled to issue a ruling next year and pending successful navigation of the inevitable appeals process, a successful outcome should provide leverage to help open the Austrailian and other markets to U.S. apples.

6.Technology Transfer

Number of Other Technology Transfer1

Last Modified: 4/20/2014
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