|Rubio Ames, Zilfina|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2012
Publication Date: 3/1/2013
Citation: Feliziani, E., Smilanick, J.L., Margosan, D.A., Mansour, M.F., Romanazzi, G., Gu, S., Gohil, H., Rubio Ames, Z. 2013. Preharvest fungicide, potassium sorbate, or chitosan use on quality and storage decay of table grapes. Plant Disease. 97:307-314. Interpretive Summary: Table grapes will rot after harvest and most common solution to control rot under commercial conditions is to apply fungicides before harvest and use sulfur dioxide after harvest, but residues of these can make the fruit more difficult to export or market domestically to some buyers. The purpose of this work was to evaluate the effectiveness of alternatives to vineyard fungicide applications to control postharvest decay and compare these to a conventional fungicide application practices. This research provided insights into better management decisions for grape growers to increase the storage life of fresh table grapes so they can minimize or avoid fungicide residues in consumers' diets.
Technical Abstract: A program of four fungicides, potassium sorbate, or one of three chitosan formulations was applied to clusters of ‘Thompson Seedless’ grapes at berry set, pre-bunch closure, veraison, and 2 or 3 weeks before harvest. The natural incidence of postharvest gray mold after cold storage for 6 weeks was reduced by potassium sorbate, fungicides, or both together, in 2009 and 2010. Grape sugar content after potassium sorbate use was higher than the controls. In 2011, the experiment was repeated with three chitosan products (OII-YS, Chito Plant, and Armour-Zen) added. Chitosan or fungicide treatments significantly reduced the natural incidence of postharvest gray mold. Infection of berries inoculated with Botrytis cinerea conidia was significantly reduced by two of the chitosan treatments and the fungicides. None harmed berry quality, and all increased endochitinase activity. Chitosan decreased berry hydrogen peroxide content. One of the chitosan formulations increased quercetin, myricetin, and resveratrol content of the berry skin. In another experiment, ‘Princess Seedless’ grapes treated with one of several fungicides before 4 or 6 weeks of cold storage, had less decay than the control. Fenhexamid was markedly superior to the other fungicides for control of both the incidence and spread of B. cinerea during storage.