Effect of 2,3,5-Triiodobenzoic Acid on the Susceptibility of Soybeans to Macrophomina phaseolina. T. K. Kroll, Graduate Assistant, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. L. D. Moore, Associate Professor, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Plant Dis. 65:483-485. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-483.

The growth regulator 2,3,5-triiodobenzoic acid (TIBA) was tested for its effects on the susceptibility of the soybean cultivars Amsoy 71 and Wayne to disease incited by Macrophomina phaseolina. Foliarly applied TIBA, 70 g/ha, at flowering decreased microsclerotial development on Amsoy 71 and changed the pattern of vessel elements. Vessel elements were produced only during early and late season growth. TIBA was directly fungitoxic to M. phaseolina at 100 µg/ml Czapek Dox broth medium. When the organism was cultured on TIBA-treated soybean root and stem tissue agar media or on untreated tissue agar media amended with TIBA, no direct or induced fungitoxic response was noted.