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4-Hydroxybenzaldehyde and Vanillin as Toxins Formed in Leaf Wound Sap of Phaseolus lunatus. A. A. Bell, Former Assistant Professor, University of Maryland, College Park; now Research Plant Pathologist, Crops Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 60:161-165. Accepted for publication 29 August 1969. DOI: 10.1094/Phyto-60-161.

On the basis of Rf values, chromogenic reactions, and ultraviolet-absorption spectra in ethanol and sodium ethoxide, the fungitoxic aldehydes found in leaf wound sap of Phaseolus lunatus were identified as 4-hydroxybenzaldehyde and 3-methoxy-4-hydroxybenzaldehyde (vanillin). A molecular concentration of hydrocyanic acid equivalent to the combined concentration of the aldehydes was evolved concurrent with aldehyde formation. Two glycosides separated by paper chromatography yielded hydrocyanic and 4-hydroxybenzaldehyde when treated with beta-glucosidase (from almonds). The authentic aldehydes, as well as protocatechuic aldehyde, were more toxic to germination of uredospores of Uromyces phaseoli and Puccinia sorghi, and teliospores of Ustilago avenae and U. nuda, than corresponding benzoic or cinnamic acid derivatives. Cyanohydrins derived from the aldehydes were more than 10 times as toxic as the aldehydes. Biochemical reactions are proposed to explain the accumulation of the aldehydes.