Oxidative Stress in Entomopathogenic Fungi and Its Potential Role on Mycoinsecticide Enhancement

Abstract

Entomopathogenic fungi (EF) are used worldwide as environmentally friendly mycoinsecticides. A successful invasion process depends on the fungal ability to cope with several stress factors, such as osmotic stress, temperature, UV radiation, and oxidative stress. Reactive oxygen species (ROS) can appear due to either previous environmental stresses or endogenous metabolic changes. Moreover, ROS may be either part of the host defense against fungi or the fungus itself can release ROS in the hemolymph to overcome insect defenses. Regardless of its source, fungi must mitigate ROS damage in their cells. Antioxidant response in fungi involves the action of enzymes as well as non-enzymatic compounds. Oxidative stress and antioxidant responses are known to have several direct and/or indirect consequences in fungal adaptation. Nutritive stress produced by non-preferred carbohydrate sources in conidia production can increase ROS scavengers consequently enhancing UV tolerance. Additionally, growth in long chain cuticular hydrocarbons triggers ROS production and antioxidant gene induction, leading to more virulent conidia. Also, ROS can act as signaling molecules for cell differentiation into new propagules such as microsclerotia and mycelial pellets that tolerate desiccation and produce new infective conidia in the field. In this chapter we will summarize ROS sources and antioxidant scavengers during conidial production and fungal invasion into their hosts, and the beneficial consequences for stress tolerance, virulence and cell differentiation that can arise from these initial drawbacks.