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Genetic Characterization of Binucleate Rhizoctonia Species Causing Web Blight on Azalea in Mississippi and Alabama

May 2007 , Volume 91 , Number  5
Pages  616 - 623

T. A. Rinehart and W. E. Copes , United States Department of Agriculture, Agricultural Research Service, Thad Cochran Southern Horticultural Laboratory, 810 Highway 26 West, Poplarville, MS 39470 ; and T. Toda and M. A. Cubeta , North Carolina State University, Department of Plant Pathology, Center for Integrated Fungal Research, 225 Partners III, Raleigh, NC 27695-7567



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Accepted for publication 11 December 2006.
ABSTRACT

Web blight on containerized azalea is an annual problem for commercial nurseries during summer months in the southern United States. Losses to web blight are associated with the cost of fungicide applications, delayed marketing of diseased plants, and plant death. Two hundred and eleven isolates of binucleate Rhizoctonia were recovered from azalea leaves with web blight symptoms from two nurseries in Mississippi and Alabama over 3 years. The internal transcribed spacer region (ITS) of the ribosomal DNA (rDNA) was sequenced from all isolates to determine genetic identity. A single anastomosis group (AG) of binucleate Rhizoctonia represented 92% of the samples collected from infected leaves. Genetic data and hyphal fusion experiments confirmed that these isolates belong to AG-U, which was recently identified from root and stem infections on miniature rose in Japan. Isolates of binucleate Rhizoctonia belonging to anastomosis groups AG-R, CAG-7 (=AG-S), and AG-G were also identified in the sample in low frequency. This is the first report of the occurrence of binucleate Rhizoctonia AG-U in the United States.


Additional keywords: Ceratobasidium, rhododendron

The American Phytopathological Society, 2007