VIEW ARTICLE

Physiology and Biochemistry

Hydrogen Cyanide Potential During Pathogenesis of Sorghum by Gloeocercospora sorghi or Helminthosporium sorghicola. D. F. Myers, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address of senior author: Department of Plant Pathology, Montana State University, Bozeman, MT 59717; W. E. Fry, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 68:1037-1041. Accepted for publication 31 January 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1037.

The production of hydrogen cyanide (HCN) may be important in diseases of cyanogenic plants such as sorghum (Sorghum bicolor, S. sudanense). We measured the hydrogen cyanide potential (HCN-p) during pathogenesis of sorghum leaves by Gloeocercospora sorghi or Helminthosporium sorghicola. Different methods of measuring HCN-p were evaluated. A new, improved method combining an enzymatic and a nonenzymatic degradation of the cyanogenic glycoside dhurrin was used to estimate HCN-p. A decrease in HCN-p in diseased primary leaves was detected first between 24 and 48 hr after inoculation. Although plants of cultivar Grazer contained about twice as much HCN-p as those of cultivar Piper, the infection of either cultivar by either pathogen reduced the HCN-p to about 10% of the original level within 3-4 days after inoculation. The HCN that volatilized from nondisrupted primary leaves of cultivar Grazer infected by G. sorghi accounted for about 14% of the original total HCN-p. Efficiency of enzymatic dhurrin degradation in sorghum primary leaves increased 2- to 4-fold between 12 and 24 hr after inoculation. The results provide a basis for relating changes in HCN-p to specific events in pathogenesis of sorghum by G. sorghi or H. sorghicola.