Submitted to: International Rhizoctonia Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 8/4/2008
Publication Date: 8/20/2008
Citation: Copes, W.E., Cubeta, M.A., Toda, T., Rinehart, T.A. 2008. Rhizoctonia Species Associated With Bark Media and Plant Strata of Container-Grown Azalea. International Rhizoctonia Symposium 20-22 August 2008, Berlin (D) p40.
Technical Abstract: Symptoms of Rhizoctonia web blight, caused predominantly by binucleate Rhizoctonia (BNR) anastomosis group U, develops annually from late-June to mid-September on container-grown azaleas (Rhododendron spp.) in the southern United States. In 2005 and 2006, ‘Gumpo White’ azalea plants with a disease severity of 35 to 60% were collected from nurseries and maintained under overhead irrigation. During late summer, 30 blighted leaves were collected, enclosed in a nylon mesh bag, and placed on the bark medium surface in each pot. Disease symptoms disappeared during the fall with growth of new leaves and no new development of symptoms. Each of 10 plants was destructively divided into eight horizontal zones in early December, February, and May. From a plant, 84, 30, and 15 samples of bark media, blighted leaves from the bags, and asymptomatic live plant stems, respectively, were plated on Ko and Hora medium to assess the frequency of seasonal recovery and year-to-year survival of Rhizoctonia spp. Plant stems were assessed in June and July also. A total of 3600 isolates were recovered. Recovery frequency was high from the blighted leaves (66 to 98%) at all sample dates. Rhizoctonia spp. were recovered more frequently from the top 3 cm of bark media (17 to 55%) and the lowest 2 cm of plant trunk (68 to 100%) than from bark media and stem samples further from the dead leaf layer. Recovery levels were seasonally lowest in May from the middle zone of bark media and in June from stems in the upper canopy. The identification of 200 representative isolates (84% are binucleate) is currently being conducted using sequencing of rDNA ITS regions and hyphal anastomosis criteria. The research suggests that once individual container-grown azalea plants become infested, BNR persists year-to-year in the container. This information indicates sanitation and handling methods that minimize pathogen transmission to disease-free plants could be a beneficial disease control strategy.