Toxicity of ozone gas to conidia of Penicillium digitatum, penicillium italicum, and botrytis cinerea and control of gray mold on table grapes

Abstract

Penicillium digitatum, Penicillium italicum, and Botrytis cinerea attack fresh fruit and cause significant postharvest decay losses. The toxicity of ozone (O-3) gas at different relative humidities to control their conidia was determined. Conidia distributed on cover glasses were exposed to an atmosphere containing 200-350 mu LL-1 of O-3 gas at 35%, 75%, and 95% relative humidity (RH) at 25 degrees C. O-3 gas was produced by UV light generators and passed through three 500 mL solutions of saturated MgCl2 (35% RH), NaCl (75% RH), or K2SO4 (95% RH). O-3 and RH inside the chamber were monitored. O-3 exposures were quantified as concentration x time products adjusted to 1 h (mu LL-1 x h). After exposure to O-3 for varying periods, the conidia were removed from the chamber, placed on potato dextrose agar and their germination observed. Conidia died more rapidly at higher humidity than at lower humidity. and P. digitatum and P. italicum were more resistant to O-3 than B. cinerea. At 95% RH, 99% of the conidia of P. digitatum, P. italicum, and B. cinerea were incapable of germination after O-3 exposures of 817, 732, and 7024 mu LL-1 x h, respectively. At 75% RH, similar inhibition required exposures of 1781, 1274, and 1262 mu LL-1 x h, respectively. At 35% RH, O-3 toxicity declined markedly, and 99% mortality required 11,410, 10,775, and 7713 ILL x h, respectively. These values can be used to select O-3 gas exposures needed to control these conidia. Conidia of B. cinerea were sprayed on to the surface of table grapes and 2 h later the grapes were exposed to 800-2000 mu LL-1 x h of O-3. O-3 at 8004 mu LL-1 x h or more reduced the incidence of infected berries by 85% and 45% on 'Autumn Seedless' and 'Scarlet Royal' grapes, respectively. Fumigation with O-3 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.