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Management of Xanthomonas Leaf Blight of Onion with Bacteriophages and a Plant Activator

July 2007 , Volume 91 , Number  7
Pages  871 - 878

Jillian M. Lang , Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins 80523-1177 ; David H. Gent , U.S. Department of Agriculture-Agricultural Research Service, National Forage Seed Production Research Center, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-8539 ; and Howard F. Schwartz , Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins 80523-1177



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Accepted for publication 5 March 2007.
ABSTRACT

Xanthomonas leaf blight of onion (Allium cepa), caused by Xanthomonas axonopodis pv. allii, continues to be a challenging and yield-threatening disease in Colorado and other regions of onion production worldwide. Studies were conducted to develop management strategies for this disease that are equally effective and more sustainable than the current practices of making multiple applications of copper bactericides. Mixtures of bacteriophages and the plant defense activator, acibenzolar-S-methyl, were evaluated under field and greenhouse conditions for their abilities to reduce Xanthomonas leaf blight severity. Bacteriophage populations in the phyllosphere of onion were monitored over time. Bacteriophage populations persisted on onion leaves for at least 72 to 96 h under field and greenhouse conditions, respectively. Under field conditions at one location, biweekly or weekly applications of bacteriophages reduced disease severity by 26 to 50%, which was equal to or better than weekly applications of copper hydroxide plus mancozeb. Acibenzolar-S-methyl also successfully reduced disease severity by up to 50% when used alone preventatively or followed by biweekly bacteriophage applications. Reductions in disease severity generally were not associated with improvements in onion bulb size or yield. Integration of bacteriophage mixtures with acibenzolar-S-methyl appears to be a promising strategy for managing Xanthomonas leaf blight of onion, and could reduce grower reliance on conventional copper bactericide applied with ethylenebisdithiocarbamate fungicides.


Additional keywords: bacterial blight , biological control , integrated pest management , systemic acquired resistance

© 2007 The American Phytopathological Society