Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/4/2005
Publication Date: 4/1/2006
Citation: Romanazzi, G., Gabler, M.F., Smilanick, J.L. 2006. Preharvest chitosan and postharvest uv irradiation treatments suppress gray mold of table grapes. Plant Disease. 90: 445-450. Interpretive Summary: Table grapes often rot after harvest due to gray mold, caused by infection of the fungus Botrytis cinerea. Fungicides are usually applied to control this problem, however, in this work to alternative treatments, ultraviolet light illumination and application of the natural biopolymer chitosan, were combined to control gray mold. In addition to reducing gray mold, the combination of treatments also elicited production of catechin and resveratrol in the grapes, which are natural antimicrobial compounds with demonstrated human health benefits.
Technical Abstract: The effectiveness of chitosan treatment of table grape, alone or in combination with ultraviolet C (UV-C) radiation to control postharvest gray mold caused by Botrytis cinerea, was determined in California, United States. The influence of these treatments on catechin and resveratrol contents and chitinase activity in grape berry skins was also assessed. Clusters of cvs Thompson Seedless, Autumn Black, and Emperor were sprayed in the vineyard with 1% chitosan, then harvested daily for 5 days. Promptly after harvest, they were inoculated with B. cinerea. Decay incidence and disease severity were significantly reduced by chitosan, which was most effective on berries harvested 1 or 2 days after treatment. In another experiment, grape berries were sprayed in the vineyard with chitosan, harvested 2 days later, irradiated for 5 min with UV-C treatments applied to cv Autumn Black or selection B36-55 were synergistic in reducing gray mold incidence and severity compared with either treatment alone. Preharvest chitosan treatment increased neither concentration of catechin or resveratrol nor activity of chitinase in berry skin. Conversely, UV-C irradiation, alone or combined with chitosan treatment, induced catechin in cv Autumn Black berries and trans-reseveratrol in both cv Autumn Black and selection B36-55.