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Sensitivity of Sugarcane Clones to Toxin from Helminthosporium sacchari as Determined by Electrolyte Leakage. R. P. Scheffer, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824; R. S. Livingston, technician, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824. Phytopathology 70:400-404. Accepted for publication 8 October 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-400.

Host-selective toxin from Helminthosporium sacchari was processed to a high level of purity and was used in assays of relative sensitivities of sugarcane clones. An assay based on toxin-induced loss of electrolytes from leaf tissue was more precise than were assays based on visible expressions of toxicity. Electrolyte losses from tissues exposed to toxin for 1 hr and monitored for 18 hr equalled those of tissues exposed to toxin continuously for 18 hr. The rate of loss increased for 23 hr, then decreased. When toxin concentrations were increased from 0.1 to 0.5 μg/ml, electrolyte loss increased linearly. High concentrations (50 μg/ml) resulted in gradual but complete loss of ability of tissues to retain electrolytes. Sugarcane clone reactions varied from very sensitive (affected by toxin at 0.01 μg/ml) through several intermediate levels to very insensitive (unaffected by at least 100 μg/ml). In general, sensitivity or insensitivity to toxin correlated with susceptibility or resistance of the fungus. However, the correlation did not hold for three clones of 17 tested. The data suggest that toxin may determine pathogenicity to some clones but not to others, and that toxin should be used with caution in screening for disease resistance.