Repeated treatments with acetic acid vapors during storage preserve table grapes fruit quality

Postharvest losses on table grapes caused by Botrytis cinerea, are controlled with SO2 fumigations carried out every 7 or 10 d. The use of this gas is becoming more difficult to justify because of undesirable effects on the fruit and the increasing concern for human health. Objectives of the paper were to evaluate if repeated treatments with acetic acid (AC) during storage, were effective in preserving table grapes quality, comparing in addition the effects of AC and SO2 treatments. Experiments carried out in vitro on B. cinerea proved that the effect of AC on mycelia growth and conidia germination was related not only to the dose and exposure period, but also to the elapsed time between fungal inoculation and treatment. The reinoculum test demonstrated that a treatment with 20 ?L L-1 of AC for 15 min had a fungicidal effect. A laboratory test was performed, to evaluate in vivo the effectiveness of AC on B. cinerea. Results suggested that higher doses were needed to control the pathogen. On naturally infected table grapes two storage experiments were carried out: in the first trial a single AC concentration of 50 ?L L-1 was used to perform one or two fumigations after 4 or 8 weeks (w), while three different AC concentrations (30, 50 and 75 ?L L-1) were used in the second trial and fumigations were repeated 5, 3 and 2 times respectively. Treatments lasted 15 min and fruit was stored for 8 w at 5 °C and 90% RH, followed by 3 d of a simulated marketing period. All treatments reduced gray mold incidence, with respect to untreated fruit, after 8 w of storage, but repeated treatments resulted the most effective. Two fumigations at 50 ?L L-1 or 5 fumigations at 30 ?L L-1 reduced gray mold incidence by 63.6 or 57.1% respectively. Fruit weight loss was significantly reduced by all treatments, while quality parameters resulted not to be affected by any of the treatments.