Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/4/2010
Publication Date: 2/1/2011
Citation: Ozkan, R., Smilanick, J.L., Akgun Karabulut 2011. Toxicity of ozone gas to conidia of Penicillium digitatum, P. italicum, and Botrytis cinerea and control of gray mold on table grapes. Postharvest Biology and Technology. 60:47-51. Interpretive Summary: Fresh produce can rot soon after harvest due to infections by rot pathogens that are mostly fungi. Ozone gas, a treatment approved for use on fresh produce by regulatory agencies, was applied to the spores of several of the most common fungi that cause fresh produce to rot to determine the concentration of ozone gas needed to control them. The concentration of ozone gas were determined, then applied to fresh grapes at a rate that kills spores of the gray mold fungus, and the treatment significantly prolonged the period the fruit were free from rot after harvest. Ozone gas has the potential to be a useful treatment to prolong the postharvest life of fresh products that can tolerate the relatively high rates needed to control fungi.
Technical Abstract: Penicillium digitatum, P. italicum, and Botrytis cinerea attack fresh fruit and cause significant postharvest decay losses and the toxicity of ozone (O3) gas at different relative humidities to control their conidia was determined. Conidia were exposed to an atmosphere containing 200 to 350 µL L-1 of O3 at 35%, 75%, and 95% relative humidity (RH) at 25 C. Before exposure to O3 gas, the conidia were distributed on cover glasses and conditioned for 2 h at 95% RH or 12 h at 35% or 75% RH. O3 gas was produced by UV light generators and passed through three 500 ml solutions of saturated MgCl2 (35% RH), NaCl (75% RH), or KSO4 (95% RH). O3 concentrations and RH inside the chamber were monitored. O3 exposures were quantified as concentration x time products adjusted to 1 h (µL L-1 x h). After exposure to O3 for varying periods, the conidia were removed from the chamber, placed on potato dextrose agar (PDA), and their germination was determined after 18 h incubation at 20 C. Conidia died more rapidly at higher humidity than at lower humidity, and P. digitatum and P. italicum were more resistant to O3 than B. cinerea. At 95% RH, 99% of the conidia of P. digitatum, P. italicum, and B. cinerea were incapable of germination after O3 exposures of 817, 732, and 702 µL L-1 x h, respectively. At 75% RH, similar inhibition required exposures of 1,781, 1,274, and 1,262 µL L-1 x h, respectively. At 35% RH, O3 toxicity declined markedly, and 99% mortality required 11,410, 10,775, and 7,713 µL L-1 x h, respectively. These values can be used to select O3 gas exposures needed to control these conidia. Conidia of B. cinerea were sprayed on to the surface of table grapes ‘Autumn Seedless’ and ‘Scarlet Royal’ and 2 h later the grapes were exposed to 800 to 2000 µL L-1 x h of O3. After incubation for one week at 20 C, concentrations of 800 µL L-1 x h of O3 or more reduced the incidence of infected berries by 85 and 45% on ‘Autumn Seedless’ and ‘Scarlet Royal’ grapes, respectively. O3-treated grapes that did develop infections had small, non-sporulating lesions, while the control grapes were covered with aerial mycelium and conidia. Fumigation with O3 can control postharvest pathogenic fungi on commodities that tolerate this gas, or it can be applied to disinfect processing equipment and storage rooms when the produce is not present.