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Location of Macrophomina phaseoli on Soybean Plants Related to Culture Characteristics and Virulence. O. D. Dhingra, Graduate Research Assistant, Department of Plant Pathology, University of Illinois, Urbana 61801; J. B. Sinclair, Professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 63:934-936. DOI: 10.1094/Phyto-63-934.

Single hyphal-tip isolations were made from 15 cultures of Macrophomina phaseoli (Rhizoctonia bataticola) isolated separately from the roots, stem, petiole, pod, and seed for each of three field-grown soybean plants. Root isolates from each of the three plants caused 80-100% mortality of wound-inoculated seedlings within 10 days or produced severe rosetting on surviving seedlings. Petiole, stem, and pod isolates caused 60-100, 30-60, and 10-20% mortality, respectively. After 4 days, sclerotia from cultures of root isolates ranged from 122-188 × 77-127 µ and stem isolates 84-100 × 60-71 µ. Growth rate and colony type varied among isolates from the same plant, and between isolates from different plants, on different media, and within incubation temperatures (15, 20, 25, 30, and 35 C) on potato-dextrose agar. At 30 C, all stem isolates produced fluffy growth, all root isolates were partially fluffy, and the remainder showed appressed growth. The maximum growth was at 35 C for pod and seed isolates and two isolates from root, petiole and stem; and 30 C was optimum for the other three isolates. Each isolate performed consistently in three separate trials.

Additional keywords: charcoal rot, seedling blight.