Alternative means to conventional fungicides in gray mold postharvest control on table grapes

Gray mold, caused by Botrytis cinerea, is the main postharvest disease of table grapes. It can develop in the vineyard and spread rapidly among the berries after harvest, during transport, cold storage and shelf life.

In conventional farming, the bunches are generally treated with fungicides after flowering, at pre-bunch closure, at veraison, and later according to the harvesting time. The harvested bunches are stored by using sulfur dioxide, but the use of synthetic fungicides and of sulfur dioxide is not allowed for organic produce, furthermore the demand for environmentally friendly storage methods continues to increase.

For these reasons, in the last decades several studies were conducted to develop methods alternatives to chemical fungicides to control postharvest decay of fruit and vegetables.

In 2012, a group of Italian, Israeli and American researchers (Romanazzi et al., 2012) has published a review on ‘Postharvest Biology and Technology’ Journal about the alternatives means to the use of fungicides in the control of postharvest gray mold of table grapes.

The work reports the results published on this topic from 2006 to 2010 on the main international Journals, the authors have described the effectiveness to control gray mold of table grapes of following methods:

Biocontrol agents, such as Muscodor albus and Hansienaspora uvarum;
Natural antimicrobial compounds, such as salts (potassium tetraborate, sodium carbonate, sodium bicarbonate, calcium chloride), chitosan, Aloe vera gel coating, essential oil of Ocimum sanctum, Thymus vulgaris and Satureya hortensis;
Sanitizers classified as GRAS compounds (Generally Recognized As Safe), such as acetic acid, electrolyzed oxiding water, ethanol;
Physical methods, such as UV-C irradiation, treatments with pressure lower (hypobaric) or higher (hyperbaric) than atmospheric, MAP (Modified Atmosphere Packaging) with high CO2 concentration.

The authors have stressed that a single alternative approach might not be effective enough in controlling the postharvest decay if compared to the chemical fungicides, thus they have suggested that the combination of two or more alternative means could be more beneficial. For example, the effectiveness of chitosan increases when it is used with ethanol or UV-C irradiation, also the MAP combined with essential oils, such as eugenol, thymol and carvacrol, can reduce the incidence of gray mold by at least 30% after about two months of storage at 1°C.

The authors have concluded the work describing 1) the commercial aspects of table grape chain in Italy, Israel and California and 2) the potential of using calcium chloride, as preharvest treatment, and ozone, as postharvest treatment, to obtain table grapes free from fungicide residues. Especially, the ozone could be the mean alternative to fungicides and sulfur dioxide use both to control postharvest gray mold and to be used for organic production.

The authors have listed which criteria an ideal alternative mean should have to control gray mold and are following reported:

to have effectiveness equivalent or better than the current practices;
not to damage or cause phytotoxic effects on produce;
not to compromise the organoleptic quality of produce;
to be environmentally friendly;
to be compatible with standard practices, affordable and easy to implement;
to be in agreement with principles of organic farming;
to offer substantial benefit to the technology manufacturers, which often play a pivotal role in commercialization of novel treatments.

Original study. Romanazzi G., Lichter A., Mlikota Gabler F., Smilanick J.L., ‘Recent advances on the use of natural and safe alternatives to conventional methods to control postharvest gray mold of table grapes’, 2012, Postharvest Biology and Technology, Issue No. 63, pagg. 141-147. Further info: http://www.sciencedirect.com/science/article/pii/S0925521411001633