Germination of fungal conidia after exposure to low concentration ozone atmospheres

• Conidia of six fungi that cause postharvest decay were exposed to ozone at 150 nL/L for 100 d at 2 °C.
• In ozone, 50% could not germinate after 3–4 weeks and 95% after 2–3 months.
• In air, 50% or more were alive after 3 months.
• Conidia from older cultures of Penicillium digitatum were more resistant to ozone.

The germinability of conidia of Alternaria alternata, Aspergillus flavus, Aspergillus niger, Penicillium digitatum, Penicillium expansum, or Penicillium italicum was determined periodically during exposure for approximately 100 d to a humid atmosphere of air alone or with 150 nL/L ozone at 2 °C. Conidia were exposed on glass coverslips that were removed from chambers at intervals of one week and the germination of 100 conidia of each species was assessed after incubation for 24 h on potato dextrose agar. The period in d when 50% or 95% (ET50 and ET95, respectively) could not germinate and 95% confidence intervals for these estimates were made using Finney's probit analysis. ET50 and ET95 estimates were approximately one month and two to three months, respectively. Some natural mortality of the conidia occurred during these periods, so the entire decline in germinability was not solely due to ozone. The age of the culture from which conidia were collected influenced their susceptibility to ozone. Conidia were harvested from 7, 14, 21, and 28 d old potato dextrose agar cultures of P. digitatum and exposed to 13,000 nL/L ozone at 2 °C. After 48 h of exposure to ozone, none of the conidia from the seven-day old culture germinated, while 30–35% of conidia from 14, 21, or 28 d in age cultures germinated.