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Elutriation Procedures for Quantitative Assay of Soils for Rhizoctonia solani. C. A. Clark, Research Associate, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607, Present address of senior author: Department of Plant Pathology, Louisiana State University, Baton Rouge, LA 70803; J. N. Sasser(2), and K. R. Barker(3). (2)(3)Professors, respectively, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607. Phytopathology 68:1234-1236. Accepted for publication 17 February 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1234.

Procedures for the use of a semiautomatic elutriator to assay soils for Rhizoctonia solani are described and compared with a wet-sieving technique. The standard procedure involves elutriation of 500-cm3 samples of soil for 8 min. Debris collected on a 0.425-mm sieve is suspended in 2% water agar and after 18 to 24-hr of incubation colonies of R. solani are identified by observation at 10 to 400 on the assay plates. Compared to the wet-sieving technique, the elutriation procedure is more rapid and has a lower threshold of detection. It allows identification of colony origin, and can be conducted simultaneously with certain nematode assays. Rhizoctonia solani populations from 29 cotton fields in the coastal plain of North Carolina range from 0 to 35 propagules/500 cm3. Colonized segments of cotton stalks and roots were frequently observed as sources of R. solani.

Additional keywords: cotton seedling diseases, Gossypium hirsutum L.