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An Assay for Helminthosporium victoriae Toxin Based on Induced Leakage of Electrolytes from Oat Tissue. K. E. Damann, Jr., Graduate Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824; J. M. Gardner(2), and R. P. Scheffer(3). (2)(3)Graduate Assistant and Professor, respectively, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 64:652-654. Accepted for publication 20 November 1973. DOI: 10.1094/Phyto-64-652.

Rate of electrolyte loss from treated susceptible oat tissues was used to assay for the host-selective toxin of Helminthosporium victoriae. A direct relationship was found between toxin concn and rate of electrolyte loss, as measured by conductance of ambient solutions. Leakage rates increased with increases in toxin exposure time (1 to 120 min) and temp (5-24C). High concns (>10.0 µg/ml) induced no further leakage, indicating a saturation effect. Rates of leakage in response to subsaturating concns were linear for at least 3 hr and were used to quantify toxin by its effects. Standardized procedures are necessary for reproducible assays.