Effects of simulated solar radiation on conidial germination of Metarhizium anisopliae in different formulations

The effects of exposure time to simulated solar radiation on conidial germination of Metarhizium anisopliae were evaluated with different formulations to determine whether some of them could enhance the ultraviolet (UV) tolerance of conidia. Conidial suspensions were prepared in water plus 10% emulsifiable oils; vegetable oil; mineral oils; and in water plus 0.05% Tween 80. Equal volumes (7.2 mu l) of each 1 x 10(8)/ml conidial suspension were placed into Petri dishes, and exposed to 2, 4 and 6 h solar radiation from an 'Oriel' sunlight simulator. Unexposed plates of all formulations were the controls. After irradiation, the formulations were diluted with equal volumes of Shellsol T or 0.05% Tween 80, and the resultant suspensions incubated on Sabouraud-Dextrose-Agar at 27 +/- 0.5 degrees C. Conidial viability was assessed after 24 and 48 h incubation. Germination decreased for all treatments when the time of exposure to simulated solar radiation increased. Peanut oil, Shellsol plus Ondina, water plus Emoleo(R), Codacide(R), Natur'l oil(R), Ashlade(R) significantly enhanced conidial tolerance (P<0.05) against UV light for up to 6 h of exposure compared with water plus Cropspray(R), Cutinol(R), Actipron(R) and Tween. Unexposed control plates of all formulations showed that germination of conidia was more advanced than in those plates subjected to simulated sunlight, thus confirming that UV exposure delays germination. (C) 1998 Elsevier Science Ltd. All rights reserved.