SENSITIVITY OF PATHOGEN INOCULA TO CHLORINE DIOXIDE GAS

Abstract

There has been an increased use of chlorine dioxide (ClO2) in dump tanks and wash lines to kill pathogen spores and reduce potential disease development during storage and shipment of various fresh fruits and vegetables. In most instances, automated systems are used to generate ClO2 on site. Several growers in the Pacific Northwest are using ClO2 in place of formaldehyde to prevent the spread of Fusarium basal rot when bulbs are given hot water treatments. Controlled-release systems to produce ClO2 gas do not require specialized equipment and may have the potential to provide a convenient way to sanitize the surfaces of bulbs and flowers without having to dip or spray them with water. To determine the effectiveness of ClO2 gas in killing pathogen inocula, a series of tests were conducted by exposing inocula of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum f. sp. narcissi, Penicillium corymbiferum and Rhodococcus fascians on glass cover slips to various concentrations of gas for one hour at 20°C. Exposure of inocula to 5 mg ClO2/L (the lowest rate tested) reduced viability by 79 to 100%. At 25 mg ClO2/L, 92 to 100% of the inocula were killed. If additional studies find similar results with inocula on the surfaces of bulbs and cut flowers and there is no crop injury, this controlled release technology has the potential to provide growers with another approach for reducing losses associated with postharvest diseases during storage and shipment of bulbs and cut flowers.