Hydrogen Cyanide Potential During Pathogenesis of Sorghum by Gloeocercospora sorghi or Helminthosporium sorghicola

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Abstract
The production of HCN may be important in diseases of cyanogenic plants such as sorghum (Sorghum bicolor, S. sudanense). The HCN potential (HCN-p) during pathogenesis of sorghum leaves by G. sorghi or H. sorghicola was measured, using different methods. 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 24-48 h after inoculation. Although plants of ''Grazer'' contained about twice as much HCN-p as those of ''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 ''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 12-24 h 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.