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

Abstract

Ultraviolet radiation from sunlight is probably the most detrimental environmental factor affecting the viability of entomopathogenic fungi applied to solar-exposed sites (e.g., leaves) for pest control. Most entomopathogenic fungi are sensitive to UV radiation, but there is great inter- and intraspecies variability in susceptibility to UV. This variability may reflect natural adaptations of isolates to their different environmental conditions. Selecting strains with outstanding natural tolerance to UV is considered as an important step to identify promising biological control agents. However, reports on tolerance among the isolates used to date must be analyzed carefully due to considerable variations in the methods used to garner the data. The current review presents tables listing many studies in which different methods were applied to check natural and enhanced tolerance to UV stress of numerous entomopathogenic fungi, including several well-known isolates of these fungi. The assessment of UV tolerance is usually conducted with conidia using dose-response methods, wherein the UV dose is calculated simply by multiplying the total irradiance by the period (time) of exposure. Although irradiation from lamps seldom presents an environmentally realistic spectral distribution, laboratory tests circumvent the uncontrollable circumstances associated with field assays. Most attempts to increase field persistence of microbial agents have included formulating conidia with UV protectants; however, in many cases, field efficacy of formulated fungi is still not fully adequate for dependable pest control.

Riboflavin induces Metarhizium spp. to produce conidia with elevated tolerance to UV ‐B, and upregulates photolyases, laccases and polyketide synthases genes

“…; Fernandes et al . ). Amongst these EF, M. acridum is well known for its notable tolerance to UV‐B radiation (Morley‐Davies et al .…”

“…Among these fungi, Metarhizium is the most investigated genus for microbial control of arthropod pests and kill their arthropod hosts. Additionally, their success may be limited by their vulnerability to abiotic stresses, particularly high temperatures Rangel et al 2010;Barreto et al 2016) and ultraviolet radiation (UV), UV-A and UV-B (Braga et al 2001a(Braga et al , 2001b(Braga et al , 2001c(Braga et al , 2001dRangel et al 2004Rangel et al , 2005Fernandes et al 2007;Fang et al 2010;Fernandes et al 2015).…”

“…, Lecanicillium lecanii Zare & Gams (=Verticillium lecanii) and Lecanicillium aphanocladii Zare & Gams (=Aphanocladium album) (Braga et al 2002). UV radiation may reduce conidial viability of EF and cause delayed germination of surviving conidia Fernandes et al 2015). Amongst these EF, M. acridum is well known for its notable tolerance to UV-B radiation (Morley-Davies et al 1995;Fargues et al 1996), suggesting that this species may be important in investigating mechanisms involved in fungal protection against UV-B radiation (Braga et al 2001a(Braga et al , 2001b(Braga et al , 2001c.…”

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

“…Thus, the selection of strains with the best inherent tolerance to UV is an important step to select the most promising entomopathogenic fungi as biological control agents. Isolate screening for better tolerance to UV radiation as documented by Fernandes et al (2015) as well as screening for superior tolerance to heat and higher virulence as documented elsewhere (Alston et al 2005;Rangel et al 2005Rangel et al , 2010Fernandes et al 2008Fernandes et al , 2009Fernandes et al , 2010Fernandes et al , 2011 are important for the successful biological control of insects in agriculture. Although the use of UV lamps in the laboratory does not represent the complexity of the field tests, it does provide a useful technique to help find ways to increase the resistance to UV radiation of entomopathogenic fungi, which will eventually undergo the ultimate tests under field conditions.…”

“…The article by Fernandes et al (2015) covers aspects of UV radiation from sunlight, which is the most detrimental environmental factor that affects the viability of entomopathogenic fungi applied for pest control. The outcomes of studies on this topic can be affected by two compounding factors: the sensitivity of most entomopathogenic fungi to UV radiation and the variability of the laboratory methods that are used to study the UV sensitivity of entomopathogenic fungi.…”