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Damage and recovery from UV-B exposure in conidia of the entomopathogens Verticillium lecanii and Aphanocladium album

     Department of Biology, Utah State University, Logan, Utah 84322-5305

Stephan D. Flint

     Department of Rangeland Resources and the Ecology Center, Utah State University, Logan, Utah 84322-5230

Charles D. Miller
Anne J. Anderson
Donald W. Roberts ¹

     Department of Biology, Utah State University, Logan, Utah 84322-5305

We evaluated the effects of exposure to doses supplied at an environmentally realistic intensity of UV-B radiation (800 mW m^-2 weighted irradiance) on the culturability and germination of selected strains of the entomopathogenic Hyphomycetes Verticillium lecanii and Aphanocladium album. Increased UV-B exposure decreased relative percent culturability for all strains. Four hours of exposure to UV-B were sufficient to reduce the culturability close to zero. The LT₅₀ (50% lethal time) ranged from 120 ± 5 min for the V. lecanii strain ARSEF 6430 to 86 ± 14 min for the A. album strain ARSEF 6433. A strong delay in the germination of surviving conidia was observed. To determine the occurrence of photoreactivation in these two genera, we evaluated the effect of exposure to visible light after exposure to UV-B radiation. There was no significant difference in relative culturability between conidia exposed to visible light after UV-B exposure compared to those incubated in the dark after UV-B exposure. This indicates that photoreactivation, if it occurs, must have limited importance in the repair of the damage induced by UV-B radiation in these two genera.

Key words: biological control, conidial germination, conidial photobiology, Hyphomycetes, photoreactivation, UV damage

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