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

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.

Vascular Streak Dieback of cacao in Southeast Asia and Melanesia: in planta detection of the pathogen and a new taxonomy

“…The ITS data presented here for the extype strain of C. ramicola clearly distinguish it from the morphologically similar C. theobromae. Rinehart et al (2007) and M.A.C., (unpubl.) considered C. ramicola to be most closely related to AG-U of Ceratobasidium (Rinehart et al 2007), a group that is characterized by having binucleate hyphal cells.…”

“…Pure cultures of this Ceratobasidium were isolated from the vascular tissue of wood of diseased cacao in South Sulawesi and East Java. Ceratobasidium ramicola represents a species complex that includes pathogens of azalea and rose in Japan and the USA, respectively (Hyakumachi et al 2005;Rinehart et al 2007) and more recently on carrot in Japan (Tomo Misawa, Shiro Kuninaga & Takashi Toda, unpubl. ).…”

Phylogenetic relationships of Rhizoctonia fungi within the Cantharellales

“…The close relationship existing within these isolates has been previously recognized (Hyakumachi et al 2005; Rinehart et al 2007; Sharon et al 2008; Veldre et al 2013). Isolates of AG-U have been found to recognize and undergo hyphal fusion (anastomose) with certain isolates of AG-P, and Sharon et al (2008) have suggested that AG-U is a subgroup of AG-P.…”

Weather-Based Forecasting of Rhizoctonia Web Blight Development on Container-Grown Azalea

“…the southern and eastern United States (2,13,22). Web blight symp toms typically appear in July and August, but can occur as early as June and as late as September (2,7,8,14).…”