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Fire Blight Resistance in Pyrus: Involvement of Arbutin Oxidation. C. C. Powell, Jr., Research Assistant, Department of Plant Pathology, University of California, Berkeley 94720; D. C. Hildebrand, Associate Research Plant Pathologist, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 60:337-340. Accepted for publication 19 September 1969. DOI: 10.1094/Phyto-60-337.

Arbutin was readily oxidized by commercial polyphenol oxidase (PPO) and tissue homogenates of pear. Greater oxidation occurred with homogenates of old leaves than with young ones. Hydroquinone was oxidized by homogenates (independently of arbutin) but not by PPO. Oxidation products of arbutin were toxic to Erwinia amylovora. More were formed by older leaves. Hydroquinone stimulated the oxidation of arbutin by PPO, but the degree of stimulation depended upon when the hydroquinone was added to the reaction mixture. Chromatographic evidence indicated that hydroquinone reacted with one of the oxidation products of arbutin. It is suggested that the oxidation pathway of arbutin degradation may be involved in fire blight resistance through both the formation of toxic substances and an interaction with the hydrolytic pathway.