Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/16/2011
Publication Date: 8/20/2011
Citation: Romanazzi, G., Mlikota-Gabler, F., Lichter, A., Smilanick, J.L. 2011. Recent advances on the use of natural and safe alternatives to conventional methods to control postharvest gray mold of table grapes. Postharvest Biology and Technology. doi:10.1016/j.postharvbio.2011.06.013. Interpretive Summary: Table grapes will rot after harvest unless actions are taken to stop this from happening. Now, grapes are treated commercially with sulfur dioxide gas to stop the rot, but this process can bleach the color from some of the berries and this treatment is banned from use on grapes produced in compliance with the USDA National Organic Program (NOP) rules. In this review, we describe research in the last five years to find an alternatives to sulfur dioxide that is acceptable to the NOP and similar regulatory programs in other countries.
Technical Abstract: Gray mold, caused by Botrytis cinerea, is the main postharvest decay of table grapes. It can develop in the vineyard and spread rapidly among berries after harvest, during long distant transport, cold storage and shelf life. In conventional agriculture, bunches are sprayed with fungicides after flowering, at pre-bunch closure, at veraison, and later depending on the time of harvest. Under commercial conditions, grapes may remain on the vines long after they are physiologically mature. Harvested bunches are usually stored in the presence of sulfur dioxide. However, the use of synthetic fungicides and of sulfur dioxide is not allowed on organic grapes and the study of alternative means to control postharvest decay has developed during several decades, along with the expansion of organic agriculture. This review summarizes the results published in the field within the last five years (2006-2010). We can group these approaches as follows: i) biocontrol agents; ii) natural antimicrobials; iii) GRAS type decontaminating agents; and iv) physical means. Two biocontrol agents, Muscodor albus and Hanseniaspora uvarum, have shown equal or better effectiveness than conventional means to control gray mold of table grapes in laboratory scale experiments. Currently, the bottleneck regarding the commercial use of biocontrol agents is that the registration process is comparable to that of fungicides, with similar costs but often with a narrower market, and this issue delays their transition from experimental to practical use. Natural antimicrobials, such as salts, chitosan, and plant extracts, demonstrated good results and often were applied in semi-practical or practical conditions. Several GRAS-classified sanitizers were tested to extend postharvest storage of table grapes, including acetic acid, electrolyzed oxidizing water, and ethanol, although the GRAS status of some of these compounds is dose-dependent or questionable. Physical means in reference to variations in temperature, radiation, pressure or changing atmospheric composition are all postharvest practices which require significant adaptation by the industry which is accustomed to minimal intervention during harvest. However, the use of ozone is one of successful examples moved to practical application. The optimal treatment of grapes against gray mold should consist of pre-harvest treatment or treatment during storage that will not interfere with current handling during harvest. All of these approaches act on the pathogen or on the host tissues and have different environmental consequences. Improved understanding of the various methodologies and their mode of action will lead to further optimization of the treatments and to generation of novel combinations to control postharvest decay of table grapes. The possible requirements that alternative means should have for the application in the table grape fields and/or packinghouses were summarized.