Submitted to: Plant Disease Management Reports
Publication Type: Research notes
Publication Acceptance Date: 3/1/2012
Publication Date: N/A
Citation: Interpretive Summary: Table grapes will rot after harvest and most common solution to control rot under commercial conditions is to apply sulfur dioxide, but this can make the fruit more difficult to export or market domestically to some buyers. We applied a variety of ozone treatments to replace sulfur dioxide, and some concentrations were effective enough to merit consideration for commercial use by growers. This research provided insights into a new approach to increase the storage life of fresh table grapes use that could be adopted as a practical management tool for citrus growers.
Technical Abstract: Gray mold, caused by B. cinerea, causes severe losses since it spreads easily among berries during cold storage. Currently, it is controlled by fumigation with SO2 or SO2 emitting sheets within boxes. Alternative methods, such as storage in ozone atmospheres, are needed because SO2 is banned in organic agriculture and consumer preferences to avoid SO2 residues. Storage in continuous ozone atmospheres of different concentrations on decay and berry quality was evaluated. Freshly harvested, organic ‘Crimson Seedless’ table grapes with 20.3% soluble solids were used. About 1 kg of clusters were placed into plastic clamshell boxes and 6 replicate boxes were placed in 0.116 m3 stainless steel chambers containing air or ozone at 75, 100, 150, 200, 250, 300 or 500 parts per billion (ppb) at 2C for three weeks. Chamber atmospheres were approximately 95% relative humidity by passage of the air stream through water. Two single berries were injected 20 µl of a suspension containing 106 conidia of B. cinerea (isolate 1440) per ml before placement inside two clusters inside each clamshell. Ozone concentrations in each chamber were continuously monitored throughout storage at 30 minute intervals using an UV ozone analyzer/logger and did not vary more than 10% from the designated concentrations. The air exchange rate was approximately one chamber volume every hour. Natural incidences of gray mold and other rots were recorded. Spread of gray mold from the inoculated berries was recorded as the number of infected berries near it. Aerial mycelial growth on the inoculated berries, shatter (naturally detached berries) and rachis appearance were evaluated. None of the berries appeared harmed by any of the ozone concentrations used in this study. Storage in ozone at 100 ppb or more significantly decreased the natural incidence of gray mold and its spread to infected berries near the inoculated one. Other rots in ozone-stored boxes were lower but not significantly so. The other rots were mostly Alternaria spp., with some Penicillium spp. Ozone storage at all concentrations reduced the aerial mycelium growth of B. cinerea on the surface of the inoculated berries. The benefits of increasing the ozone concentration above 100 ppb were small. The number of shattered berries was significantly reduced by all the ozone concentrations, except with 75 or 200 ppb in which it was lower, but not significantly so. The rachis appearance was little altered by any treatment, except at 150 ppb in which the rachis was greener than the control. Ozone at 100 ppb or more reduced the natural incidence and the spread of B. cinerea from an artificially infected berry, did little to influence decay by other pathogens, berry shatter or rachis appearance.