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

Abstract

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.

• biological control
• conidial germination
• conidial photobiology
• Hyphomycetes
• photoreactivation
• UV damage

We are grateful to Susan Durham for the statistical analysis, Dr. Martyn M. Caldwell for supplying the spectroradiometer, and to the State of São Paulo Research Foundation (FAPESP), São Paulo, Brazil for financial support to G. U. L. B. This project was supported in part by a NRICGP/CSREES No. 99-35302-8052 grant, and a Utah State Mineral Lease funds grant.