Conidial Pigmentation Is Important to Tolerance Against Solar‐simulated Radiation in the Entornopathogenic Fungus Metarhizium anisopliae

Abstract

The importance of conidial pigmentation to solar UV radiation tolerance in the entomopathogenic fungus Metarhizium anisopliae var. anisopliae, was estimated by comparing the effects of exposure to simulated solar UV radiation on the wild-type parent strain U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) Collection of Entomopathogenic Fungal Cultures (ARSEF) 23, which has dark green conidia, and three groups of color mutants with yellow, purple and white conidia. The comparisons included inactivation levels and the kinetics of germination of conidia exposed or not exposed to simulated solar UV radiation. In addition to significantly inactivating the conidia of different mutants, exposure to radiation delayed for several hours the germination of surviving conidia of the wild type and all mutants. In general, mutants with white conidia were more sensitive to simulated solar UV radiation than mutants with purple conidia, which were more sensitive than mutants with yellow conidia, which in turn were more sensitive than the green wild strain. A significant variation in tolerance to simulated solar radiation was observed among mutants within each color group, particularly among mutants with yellow conidia. Revertants with green conidia, DWR 179 and DWR 176, were obtained from the very sensitive UV mutants DWR 148 (yellow conidia) and DWR 149 (purple conidia), respectively. These revertants had levels of tolerance to simulated solar UV radiation similar to those of the wild-type ARSEF 23. This observation is strong evidence of the importance of green conidial pigmentation for tolerance to simulated solar UV radiation, a factor that could be manipulated to produce M. anisopliae strains with more tolerance to solar UV radiation.

Tolerance of entomopathogenic fungi to ultraviolet radiation: a review on screening of strains and their formulation

“…Variation in susceptibility of entomopathogenic fungi to UV was also related to the color of conidia, since conidial pigmentation seems to be very efficient in protecting against UV radiation, directly (Braga et al 2006;Rangel et al 2006b;Nascimento et al 2010), or indirectly because enzymes involved in pigment-synthesis pathways are also required for tolerance to abiotic stresses (Fang et al 2010). A study conducted with simulated ultraviolet sunlight reported that conidial color can influence the inactivation of conidia by the radiation, where the UV radiation may be blocked on black conidia whereas penetration of UV may vary for other pigmented conidia (Ignoffo and Garcia 1992).…”

“…Accordingly, the black conidia of Aspergillus niger presented a remarkably higher mean half-life of 14.8 h when exposed to simulated sunlight than those of all other species investigated, which included less-pigmented conidia of Beauveria, Nomuraea, Metarhizium, and a tancolored mutant of A. niger, with a half-life ranging from 1.1 h for Nomuraea rileyi to 2 h for the tan-colored mutant A. niger (Ignoffo and Garcia 1992). Color mutants of the darkly pigmented conidia M. robertsii wild-type ARSEF 23 were, in general, significantly more tolerant to UV than the less-pigmented conidia of its mutants (Braga et al 2006;Rangel et al 2006b;Nascimento et al 2010). Conversely, other studies report that the hyaline conidia of B. bassiana s.l.…”

A proteomic approach to identifying proteins differentially expressed in conidia and mycelium of the entomopathogenic fungus Metarhizium acridum

“…Incubation was in the dark at 28 C for 12 days, as previously described (Braga et al 2006). After growth, mature conidia were carefully harvested, frozen in liquid nitrogen, and stored at À80 C until use.…”

Fungal stress biology: a preface to the Fungal Stress Responses special edition

“…As both solar UV-A and UV-B can kill the conidia, as well as limit the proliferation and dispersion of fungi, it is important to summarize the available knowledge of the effects of solar radiation on conidia and on the major systems involved in the protection and repair of damage induced by solar UV radiation. The authors also assure the importance of the fungal pigmentation on conidial UV tolerance as published elsewhere (Braga et al 2006;Rangel et al 2006b). The review demonstrated that it is possible to manipulate fungi in laboratory conditions so that the resulting strains produce conidia that are more tolerant to solar radiation than wild type.…”