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Bactericidal Activity of Horseradish Peroxidase on Xanthomonas phaseoli var. sojensis. N. V. Rama Raje Urs, Research Associate, Department of Botany and Plant Pathology, Iowa State University, Ames 50010; J. M. Dunleavy, Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, and Professor, Department of Botany and Plant Pathology, Iowa State University. Phytopathology 64:542-545. Accepted for publication 1 November 1973. DOI: 10.1094/Phyto-64-542.

Horseradish peroxidase (HRP) was bactericidal on Xanthomonas phaseoli var. sojensis, a bacterium pathogenic on soybeans, in the presence of potassium iodide (KI) and hydrogen peroxide (H₂ O₂). The antibacterial activity was greatest when HRP was used at 50 µg/ml. Concns of HRP greater than 50 µg/ml did not increase the bactericidal activity. The antibacterial activity of HRP was largely prevented either by preheating the enzyme at 80 C for 20 min or by deleting H₂ O₂ in the assay system. The addition of ascorbic acid (20 nmoles/ml) to the assay system, increased the bactericidal activity of HRP. Substituting dehydroascorbic acid for ascorbic acid further enhanced the bactericidal activity of HRP, resulting in total loss in viability of the bacterium.