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2006 Plant Management Network.
Accepted for publication 7 August 2006. Published 30 October 2006.


First Report of Rhizoctonia Foliar Blight of Soybean in South Carolina


M. R. Williamson, Clemson University Plant Problem Clinic, Clemson, SC, 29634-0114; C. S. Rothrock, University of Arkansas, Fayetteville 72701; and J. D. Mueller, Clemson University Edisto Research and Education Center, Blackville, SC, 29817


Corresponding author: M. R. Williamson.  mwllmsn@clemson.edu


Williamson, M. R., Rothrock, C. S., and Mueller, J. D. 2006. First report of Rhizoctonia foliar blight of soybean in South Carolina. Online. Plant Health Progress doi:10.1094/PHP-2006-1030-01-BR.


Rhizoctonia foliar blight of soybean (Glycine max) is found in tropical and subtropical areas worldwide. It has been estimated that the disease can cause a 70% loss of foliage and pods in localized areas (2). It is caused by the fungus Rhizoctonia solani (teleomorph Thanatephorus cucumeris) anastomosis group 1, intraspecific group A (IA) and intraspecific group B (IB). Group IA generally causes severe blighting of foliage, pods, and stems within the canopy, while IB tends to form distinct leaf spots on foliage in the outer canopy. In the United States, the disease is found mainly in the states of the Gulf Coast region (2).

On 13 September 2005, the Clemson University Plant Problem Clinic received a soybean sample from Florence County, SC showing severe foliar blight which started at the base of the plant and moved upward and outward, often causing complete defoliation (Fig. 1) The weather in northeastern South Carolina was warm and rainy during much of the summer, providing conditions conducive for development of foliar blight. The disease was found in scattered areas of the field and disease incidence in these areas was 25 to 30%. The cultivars Northrup King S73-Z5 and S76-L9 were affected. Hyphae typical of Rhizoctonia species were observed on the blighted foliage, and the genus was confirmed by microscopic examination. The source of inoculum is unknown, but Rhizoctonia diseases of soybean stems, peanut stems, and pegs are common in northeastern South Carolina so infested crop residue in the soil is a likely possibility (J. D. Mueller, personal communication).


 

Fig. 1. Initial foliar lesions on soybean leaves caused by Rhizoctonia foliar blight.

 

Leaf tissue from the sample was washed in tap water and marginal areas from foliar lesions were plated on 1.6% water agar. Similar material was surface sterilized in 0.6% NaOCl and plated onto acidified potato dextrose agar (APDA). Mycelium typical of Rhizoctonia species developed after 2 to 3 days on water agar. No other pathogens were isolated on APDA. The Rhizoctonia isolates from water agar were transferred to APDA to assess morphological characteristics. Anastomosis typing was undertaken using the technique of Carling et al. (1) and officially recognized tester isolates of R. solani. Anastomosis with the AG-1 isolate RR0201 provided by Dr. Yulin Jia (USDA-ARS Dale Bumpers National Rice Research Center, Stuttgart, AR) resulted in C2 reactions, identifying the isolates as belonging to AG-1 (1,3). Sclerotia were produced in culture at 25C within 7 days (Fig. 2) These sclerotia were large, averaging 1.46 mm, with a range of 0.53 to 2.4 mm, which places the isolates in intraspecific group IA (2,3). This is the first report of this disease on soybean in South Carolina.


 

Fig. 2. Rhizoctonia solani AG1-IA isolate from soybean in South Carolina. Note large dark brown sclerotia that developed in concentric circles within 7 days after transfer to APDA.

 

Literature Cited

1. Carling, D. E., Leiner, R. H., and Kebler, K. M. 1987. Characterization of a new anastomosis group (AG-9) of Rhizoctonia solani. Phytopathology 77:1609-1612.

2. Hartman, G. L., Sinclair, J. B., and Rupe, J. C., eds. 1999. Rhizoctonia foliar blight. Pages 24-25 in: Compendium of Soybean Diseases, 4th Ed. American Phytopathological Society, St. Paul, MN.

3. Sneh, B., Burpee, L., and Ogoshi, A. 1991. Identification of Rhizoctonia Species. American Phytopathological Society, St. Paul, MN.