Effect of gaseous ozone exposure on the development of green and blue molds on cold stored citrus fruit

The effects of gaseous ozone exposure on in vitro growth of Penicillium digitatum and Penicillium italicum and development of postharvest green and blue molds on artificially inoculated citrus fruit were evaluated. Valencia oranges were continuously exposed to 0.3 +/- 0.05 ppm (vol/vol) ozone at 5 degreesC for 4 weeks. Eureka lemons were exposed to an intermittent day-night ozone cycle (0.3 +/- 0.01 ppm ozone only at night) in a commercial cold storage room at 4.5 degreesC for 9 weeks. Both oranges and lemons were continuously exposed to 1.0 +/- 0.05 ppm ozone at 10 degreesC in an export container for 2 weeks. Exposure to ozone did not reduce final incidence of green or blue mold, although incidence of both diseases was delayed about 1 week and infections developed more slowly under ozone. Sporulation was prevented or reduced by gaseous ozone without noticeable ozone phytotoxicity to the fruit. A synergistic effect between ozone exposure and low temperature was observed for prevention of sporulation. The proliferation of spores of fungicide-resistant strains of these pathogens, which often develop during storage, may be delayed, presumably prolonging the useful life of postharvest fungicides. In vitro radial growth of P. italicum, but not of P. digitatum, during a 5-day incubation period at 20 degreesC was significantly reduced by a previous 0.3 +/- 0.05 ppm ozone exposure at 5 degreesC for 4 days. Inoculum density did not influence the effect of gaseous ozone on decay incidence or severity on oranges exposed to 0.3 +/- 0.05 ppm ozone at 20 degreesC for 1 week. Susceptibility of oranges to decay was not affected by a previous continuous exposure to 0.3 +/- 0.05 ppm ozone at 20 degreesC for 1 week. A corona discharge ozone generator was effective in abating ethylene in an empty export container.