Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2006
Publication Date: 5/1/2006
Citation: Rinehart, T.A., Copes, W.E., Toda, T., Cubeta, M.A. 2006. Genetic characterization of binucleate Rhizoctonia species causing web blight on azelea in Mississippi and Alabama. Plant Disease. 91:616-623.. Interpretive Summary: The objective of our research was to genetically characterize isolates of Rhizoctonia infecting nurseries growing ornamental plants, with azalea cultivars representing at least 20% of their stock. Rhizoctonia species are soil-borne fungi that infect numerous plant species. Under hot, humid conditions the fungus causes a disease called "web blight" that defoliates plants. We collected pathogenic isolates of Rhizoctonia from two nurseries in different geographic locations in Mississippi and Alabama over three years. Our research indicates that a single anastomosis group, AG-U, causes more than 90% of damage to azaleas each year. This work is fundamental to understanding the diversity of Rhizoctonia for developing improved detection and sanitation methods to reduce crop damage.
Technical Abstract: Web blight on containerized azalea is an annual problem for commercial nurseries during the summer months in the southern US. Losses to web blight are associated with the cost of fungicides, delayed marketing of diseased plants, and plant death. Three hundred and nine isolates of Rhizoctonia recovered from azalea leaves with web blight symptoms from two nurseries in Mississippi and Alabama over three years were characterized. The internal transcribed spacer region (ITS) of the ribosomal DNA (rDNA) was sequenced from all isolates to determine genetic identity. Our results demonstrate that one anastomosis group (AG) of binucleate Rhizoctonia represented 92% of the samples from infected leaves. Genetic data suggest these isolates belong to AG-U which was recently identified from root and stem infections on miniature rose cultivars in Japan. Also found were isolates belonging to AG-T, AG-R, CAG7, and AG-G anastomosis groups. This is the first report of the occurrence of binucleate Rhizoctonia AG-T and AG-U in the US.