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Test Tube Method of Bioassay for Thielaviopsis basicola Root Rot of Soybean. J. N. C. Maduewesi, Research Associate, Michigan State University, East Lansing 48824, Present address of the senior author: Department of Botany, University of Nigeria, Nsukka, Nigeria; J. L. Lockwood, Professor of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 66:811-814. Accepted for publication 30 December 1975. DOI: 10.1094/Phyto-66-811.

Polystyrene test tubes (100 × 17 mm) containing 16g of soil infested with endoconidia or chlamydospores of Thielaviopsis basicola were found to be suitable experimental units for assessing infection of soybean by this fungus. Seedlings germinated for three days on moist paper toweling were transplanted singly into the tubes and incubated at 20 C. Increasing inoculum densities of endoconidia or chlamydospores from 101 to 105 per gram soil resulted in correspondingly increased symptom severity. At 104 per gram, symptom expression in plants grown in the tubes was well developed within 10 days, whereas comparable symptom severity of plants in pots, with other conditions the same required 20 days. The method has been used for assessing virulence of isolates of the pathogen, screening soybean cultivars for resistance, and for assaying soils for inoculum potentials of the pathogen. The advantages of the method are its economies in terms of soil, inoculum, and space, and the relatively short time required for disease development.