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Postharvest Pathology and Mycotoxins

Development of Resistance Against Geotrichum candidum in Lemon Peel Injuries. A. B. A. M. Baudoin, Former graduate research assistant, Department of Plant Pathology, University of California, Riverside 92521, Present address of senior author: Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg 24061; J. W. Eckert, Professor of plant pathology, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 75:174-179. Accepted for publication 24 August 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-174.

Injuries in the peel of lemons became progressively more resistant to infection by Geotrichum candidum when inoculated 4- 20 hr after wounding. No significant accumulation of antifungal compounds was detected in 2- or 5-day-old arrested infections. The deposition of ligninlike substances around the inoculated tissue paralleled the development of resistance. Deposition was more rapid in the flavedo than in the albedo and was stimulated more strongly around inoculated wounds than around sterile wounds. The development of ligninlike zones and of resistance were strongly inhibited by cycloheximide (1μg/ml). The ligninlike zones were not resistant to maceration when infiltrated with enzymes of the pathogen, but infiltration with water also overcame the resistance and activated arrested infections. Although the ligninlike zones may represent a defense mechanism against infection, they did not appear to be responsible for differences in resistance. The more resistant light-green or subturgid lemons produced less ligninlike material after inoculation than the more susceptible yellow or turgid fruits. The greater amount of ligninlike substances in susceptible fruit may be a response to greater fungal development.