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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGY, PATHOLOGY, AND EPIDEMIOLOGY OF EMERGING OOMYCETE PATHOGENS

Location: Foreign Disease-Weed Science

Title: Can Epiphytes reduce disease symptoms caused by Phytophthora ramorum

Authors
item Widmer, Timothy
item Dodge, Stephen

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 16, 2013
Publication Date: January 23, 2013
Citation: Widmer, T.L., Dodge, S.C. 2013. Can Epiphytes reduce disease symptoms caused by Phytophthora ramorum. Biological Control. 65:135-141.

Interpretive Summary: The pathogen that causes Ramorum blight on ornamentals is a concern to native forest species because of the potential to transport this disease throughout the United States. Rhododendrons are very susceptible to this disease causing leaf necrosis and supporting the growth of abundant spores. It is known that some chemicals can reduce the disease but there are environmental concerns and fears that the pathogen will change after repeated fungicide applications. The use of other microorganisms has been examined in other areas to control plant diseases, but has not been extensively examined as to whether it can control Ramorum blight. This study showed that many fungi have the ability to reduce the growth of the pathogen when grown together. When specific fungi and the pathogen were added to the leaf surface, disease symptoms of the leaf were reduced. This research is important in that it shows that biological control of Ramorum blight is possible if the right organism is found. This information will be important to researchers, nursery managers and regulatory agencies looking for ways to control this disease and limit the spread of the pathogen.

Technical Abstract: Leaf infection of ornamental species by Phytophthora ramorum has a significant impact on the spread of this disease. Fungicides have had limited effects on controlling this disease. With increasing concerns that repeated fungicide applications will exasperate the potential for fungicide resistance and mask symptoms, alternative control measures are desired. The potential of biological control has not been thoroughly examined. Fungi, isolated from soil, were screened in dual culture with P. ramorum for antagonistic activity. Three isolates, identified as Penicillium daleae, Metarhizium anisopliae, and Penicillium herquei, were selected for further testing on the aerial plant parts of rhododendrons. Different factors, including culture age, timing of application, dose response, and additives in the formulation, were studied for their effect on reducing leaf necrosis. Although responses were variable for the different antagonists, this study showed that fungi applied to the leaf surface could reduce necrosis caused by P. ramorum and provides a methodology to test and screen for more effective antagonists.

Last Modified: 12/19/2014
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