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The Toxins of Helminthosporium maydis (Race T) ¹

A Colorimetric Determination of the Toxins, Their Appearance in Culture and in Infected Plants

^a Department of Plant Pathology, Montana State University, Bozeman, Montana 59715

Host-specific toxins produced by Helminthosporium maydis, race T, are measured quantitatively by a chemical assay procedure involving reaction of the toxins with a sulfuric acidacetic anhydride reagent and measurement of the absorbance of the product at 330 nm. The assay was shown to measure total toxin concentrations after only limited fractionation of the culture medium. Using the assay it was possible to show that the highest amount of toxin per gram of fungus mycelium occurs early in the growth cycle of H. maydis. Toxins I, II, and V are the predominant toxins at these early times both in culture and in infected corn and wheat varieties. Some chromatographic and spectral properties of toxin V, a previously unreported toxin, are described. Since toxin V appears in culture prior to toxins I, II, III and IV, a precursor-product relationship can be suggested.

³ Present address: Department of Plant Pathology, University of Missouri, Columbia, Mo. 65201.

¹ This work was supported in part by National Science Foundation Grant GB 43192, United States Department of Agriculture Cooperative States Research Service Grant C145-2575, and is paper No. 563 of the Montana Agricultural Experiment Station.

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