Effects of UVB irradiance on conidia and germinants of the entomopathogenic hyphomycete Metarhizium anisopliae: A study of reciprocity and recovery

We tested the effects of irradiances of 920 and 1200 mW m(-2) (weighted irr adiance) on the conidia and germinants of the entomopathogenic Hyphomycete Metarhizium anisopliae, The conidia were exposed to the two irradiances for 1, 2, 4, 6, 7 or 8 h, Increased exposure decreased relative percent cultur ability, The inactivation provoked by the irradiance of 1200 mW m(-2) was h igher than for the 920 mW m(-2), with a reduction in the 50% lethal time (L T50) from 6 h 40 min to 4 h 26 min. Reciprocity was not observed when conid ia in water suspension and germinants in different stages of the germinativ e process were exposed to a 17.3 kJ m (2) total dose at both irradiance lev els, Although nonreciprocity was observed in all situations, its magnitude varied as a function of metabolic state and/or cell-cycle phase in which th e conidia were at the exposure time, The least difference between the effec ts of the two irradiance levels was observed when nongerminating conidia in suspension were exposed, and the greatest was observed when conidia were e xposed during an advanced germination phase. Doses of 6.6 and 17.3 k7 m(2) supplied through the two irradiance levels delayed the germination of the s urviving conidia, At both doses, delay was greater during exposure to the h igher irradiance. Nonreciprocity was higher for the 17.3 kJ m(-2) dose. Non reciprocity magnitude, in addition to depending on the conidial physiologic al state, also depended on dose, The results demonstrate the importance of evaluating the impact of the increase in irradiance during the different st ages of the fungal life cycle, especially during the stages which are more sensitive to UV, and not simply in dormant conidia.