ABSTRACT
The detrimental effects of solar radiation, especially the ultraviolet waveband, on quiescent conidia of Paecilomyces fumosoroseus were investigated. Conidia were irradiated by a high-intensity source, which emitted a continuous spectrum from 270 to 1100 nm and which was equipped with long-pass filters to block short wavelengths below 280, 295, 320, or 400 nm. After irradiation, conidia were tested for germinability, survival, and infectivity toward Spodoptera frugiperda larvae. It was demonstrated that the detrimental effects of light depended on irradiance in the shortest wavelengths. The UVB (280-320 and 295-320 nm) appeared to be the most detrimental part of natural radiation, although UVA (320-400 nm) was also harmful. Visible and near infrared radiations were less harmful than UV. Our results demonstrate that the irradiance of the UVB waveband should be considered as the pertinent factor for the detrimental effects of sunlight on the persistence of conidia of entomopathogenic fungi in insolated environments.
Subject(s)
Paecilomyces/radiation effects , Spores, Fungal/radiation effects , Sunlight , Ultraviolet Rays/adverse effects , Paecilomyces/growth & development , Paecilomyces/pathogenicity , Time FactorsABSTRACT
The detrimental effect of solar radiation on the survival of conidia of the entomopathogenic fungusPaecilomyces fumoroseus was studied by monitoring germinability and ability to form colonies (CFU) of conidia irradiated at two temperatures, 25 and 35 °C, harmless to shaded conidia. There was no apparent effect when spores were exposed to a high level of artificial radiation (0.66 W m(-2) UVB). However, at a lower level of irradiance (0.33 W m(-2)), effects of radiation occurred more quickly at 35 °C than at 25 °C. Under natural solar radiation, the rate of decrease in germinability or viability was doubled at 35 °C as compared to 25 °C, indicating an interaction between temperature and radiation effects under natural conditions. This interaction was not detected in indoor experiments, indicating that the spectral distribution of UV radiation has to be taken in account as well as its irradiance when studying its effects.
