Variability in response to UV-B among species and strains of Metarhizium isolated from sites at latitudes from 61 degrees N to 54 degrees S

The effects of irradiances of 920 and 1200 mW m(-2) (biologically effective weighted irradiance) were examined in 2 Metarhizium album strains, 26 M. a nisopliae strains, 1 M. flavoviride strain, and 1 M. taii strain isolated f rom sites located at latitudes from 61 degreesN to 54 degreesS. Conidia wer e exposed to UV-B from 1 to 6 h and subsequently examined for relative perc entage culturability. Total dosage received at the end of the exposure peri ods ranged from 3.3 to 19.9 kJ m(-2) for the lower irradiance and from 4.3 to 25.9 kJ m(-2) for the higher irradiance. Both the irradiance values and the doses are environmentally realistic and can be observed even in tempera te regions. The relationships between latitude of origin and UV-B tolerance were compared for the two levels of irradiance for the data from 1 and 2 h exposure. Exposure to both irradiances drastically reduced the relative pe rcentage culturability of all strains. Tolerance to UV-B varied widely amon g strains and high variation was observed for both irradiances after all pe riods of exposure. After 1 h of exposure, a difference between the two irra diance levels was detectable, and this difference was magnified at longer i rradiations. A significant quadratic relationship of decreasing UV-B tolera nce with increasing latitude was observed after exposure of I and 2 h. The shape of the relationship did not differ for the two levels of irradiance. Also, we studied the effect of 1200 MW m(-2) irradiance on conidial germina tion time in 1 M. album strain, 7 M. anisopliae strains, and 1 M. taii stra in. Exposure to UV-B delayed the germination of surviving conidia of all st rains. In general, the delay in germination was directly proportional to th e dose. (C) 2001 Academic Press.