Effect of UV-B on conidia and germlings of the entomopathogenic hyphomycete Metarhizium anisopliae

The effects of two uv irradiances (920 and 1200 mW m(-2) weighted irradianc e) on the conidia and germlings of the ARSEF 2575 and ARSEF 23 strains of M . anisopliae were studied. Conidia were exposed to the two irradiance level s for 1, 2, 3, 4, 6, or 8 l-. The 30% increase (from 920 to 1200 mW m-2) in uv irradiance caused a significant decrease in culturability following all periods of exposure and reduced the 50% lethal time (TL50) 36% for strain 2575 and 48% for strain 23. Exposure to uv radiation of only I h caused a d elay of several hours in the germination of surviving conidia. Longer perio ds of exposure delayed germination for days, demonstrating that, depending on the dose, the fungus may require a long period of time to recover and to resume germination. The results demonstrated the inability of the fungus t o germinate during direct exposure to the uv-B portion of simulated sunligh t. Both strains showed a transitory increase in uv tolerance during germina tion. The beginning of germination increased uv tolerance. However, startin g on the 6th hour of germination, a decrease in tolerance was observed, ind icating that uv tolerance varies as a function of physiological state and c ell-cycle phase.