Magnésio, zinco e cálcio como indutores de tolerância ao estresse em conídios de Metarhizium robertsii (ARSEF 2575)

Abstract

During the natural infection of insects, entomopathogenic fungi experience nutritional stress on the cuticle, oxidative stress within the cuticle, osmotic stress within the hemocoel, heat and ultraviolet (UV-B) radiation exposure after emerging from the host. These stress conditions interfere with their effectiveness as biological control agents. Several approaches have been tested to enhance the tolerance of these fungi through cross-protection, i.a fungi growth under sublethal stress exposure that induces higher conidial tolerance. This work investigated the influence of calcium, magnesium, and zinc as elicitors of stress tolerance of Metarhizium robertsii (ARSEF 2575) conidia. M.robertsii conidia were produced on minimal medium (MM = Czapek medium without sucrose), on Potato Dextrose Agar (PDA) medium as a control, or PDA supplemented with calcium phosphate at 2 and 4 g/l, magnesium sulfate at 40 and 100 mM, and zinc sulfate at 1.5 and 2 g/l. The conidia produced were then exposed to oxidative stress (menadione), osmotic stress (KCl), heat stress (45o C), and UV-B radiation (847.90 mWm-2) to evaluate their tolerances. All salts in all concentrations induced crossprotection against only to osmotic stress; nevertheless, these salts did not induce higher tolerances to oxidative stress, heat stress and UV-B radiation. Conidia produced on MM, on the other hand, induced the highest tolerance to all stress conditions. In conclusion, the study demonstrated that the use of calcium, magnesium, and zinc as elicitors can induce cross-protection in M. robertsii conidia against osmotic stress. Conidia produced on a minimal medium showed higher tolerance to all tested stress conditions. Future research should focus on optimizing growth conditions to balance stress tolerance on conidial yield, enhancing the effectiveness of these fungi as biological control agents.