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Production of Ethylene by Oats Resistant and Susceptible to Victorin. Louis Shain, Assistant Professor, Department of Plant Pathology, University of Kentucky, Lexington, 40506; Harry Wheeler, Professor, Department of Plant Pathology, University of Kentucky, Lexington, 40506. Phytopathology 65:88-89. DOI: 10.1094/Phyto-65-88.

Ethylene production by detached first leaves of oats susceptible (Vg 48-93) and resistant (C. I. 7418) to victorin, the pathotoxin produced by Helminthosporium victoriae, was determined 2 hours after a 4-hour uptake period in aqueous dilutions of victorin. Susceptible tissues were treated with victorin solutions diluted 10⁴- to 10⁸-fold; resistant ones with solutions diluted 20- to 10³-fold. The lowest concentration of victorin which caused a significant increase in ethylene evolution was a dilution of 10⁷ for susceptible, and 10² for resistant, tissues. At these concentrations, ethylene production was ca. 25 nl/g dry weight per hour for both susceptible and resistant tissues. With susceptible tissues, ethylene production increased with increased concentrations of victorin until saturation was reached at ca. 550 nl/g dry weight per hour with victorin diluted 10⁵-fold. In contrast, resistant leaves produced ca. 70 nl/g dry weight per hour with the highest concentration used (victorin diluted 20-fold). The victorin used inhibited root growth by 50% when diluted 5 × 10⁷-fold and 20-fold for susceptible and resistant plants, respectively. These results indicate that increased ethylene production, a common physiological response of plants to infection, may provide a sensitive and rapid method for assaying toxicants such as victorin.