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Hydrogen Cyanide Sensitivity in Bacterial Pathogens of Cyanogenic and Non-Cyanogenic Plants. L. A. Rust, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address: Department of Plant Pathology, Seed and Weed Science, Iowa State University, Ames 50011; W. E. Fry(2), and S. V. Beer(3). (2)(3)Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 70:1005-1008. Accepted for publication 12 April 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1005.

The cyanide sensitivity of bacterial pathogens of cyanogenic and non-cyanogenic plants was determined by observing the effects of HCN on their growth rates in buffered nutrient broth. The HCN concentration that reduced the growth rate of each strain to 50% of its growth rate in the absence of cyanide (EC50) was calculated and used to compare strains. Bacterial pathogens of cyanogenic plants appeared to be only slightly more tolerant of HCN than were bacterial pathogens of non-cyanogenic plants; these differences were not statistically significant (P = 0.05). Pseudomonads generally were more sensitive to HCN than were the xanthomonads tested. Among xanthomonads, strains of Xanthomonas manihotis, a pathogen of the highly cyanogenic plant, cassava (Manihot esculenta), appeared to be most tolerant. None of the bacteria appeared to either metabolize HCN or to adapt markedly to it. In contrast to fungal pathogens of cyanogenic plants, bacterial pathogens of cyanogenic plants are not distinctly more tolerant of HCN than are those of non-cyanogenic plants.