Disease Note.

Crater Disease and Patchy Stunting of Wheat Caused by the Same Strain of Rhizoctonia solani . Linda Meyer, Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria, 0002, South Africa . F. C. Wehner, Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria, 0002, South Africa; C. A. Kuwite, Selian Agricultural Research Institute, P.O. Box 6024, Arusha, Tanzania; and L. Piening, 5016-58 St. Lacombe, Alberta, T4L 1K7, Canada. Plant Dis. 80:1079. Accepted for publication 22 June 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1079C.

Patchy stunting of cereals has been observed in wheat farms of the Hanang area in northern Tanzania since the early 1970s. The disease is characterized by patches of stunted and chlorotic plants typical of Rhizoctonia bare patch disease affecting cereals in other parts of the world. However, seminal roots of affected plants contain nodulose swellings and sclerotial sheaths, rather than displaying girdling and rotting as with bare patch (2), and in this regard the disease closely resembles crater disease of wheat (Triticum aestivum L.) occurring on the Springbok Flats in South Africa (1). Indeed, the only difference between crater disease and patchy stunting is that the former occurs exclusively in black mont-morillonite clay soils, whereas the latter has also been observed in clay loam, silty clay loam, and silly loam soils. Crater disease is caused by a strain of Rhizoctonia solani Kuhn not anastomosing with R. solani AG-8, the causal agent of bare patch (2). Isolates of R. solani recently collected from infected wheat roots in Tanzania caused stunting of wheat seedlings and produced nodulose swellings and sclerotial sheaths in roots in artificial inoculation studies. Isolates and reisolates anastomosed with the crater disease strain of R. solani, and with an isolate of R. solani collected from roots of an umbrella-thorn tree (Acacia tortilis (Forsk.) Hayne subsp, heteracantha (Burch.) Brenan) growing in virgin soil on the Springbok Flats. It thus appears that stunting of wheat in Africa is caused by a strain of R. solani indigenous to the African continent, and that the umbrella-thorn tree could be a natural host of the fungus. Previous attempts to isolate the crater disease R. solani from grass species native to the Springbok Flats were unsuccessful. A representative crater disease isolate has been deposited in the National Collection of Fungi of the Plant Protection Research Institute, Pretoria, as PREM 49315.