Free conidia of entomopathogenic fungi modify quality traits by changing glutathione levels after an oxidant stimulus

Abstract Adverse environmental conditions (e.g. high temperature, high osmotic pressure, atmospheric changes, solar radiation, etc.) reduce the efficacy of conidia from entomopathogenic fungi used for biological control. Strategies to improve the quality traits of conidia include the introduction of sub-lethal stress treatments applied to fungal mycelium, which can improve the resistance of generated conidia to several stress factors. This work presents for the first time evidence that free conidia of Metarhizium robertsii Xoch8.1, Beauveria bassiana Tac1.1 and Cordyceps javanica CHE-CNRCB303, subjected directly to oxidant pulses (26% O 2 ), had increased osmotic stress resistance compared to control conidia (maintained at 21% O 2 ). In addition, germination and thermotolerance improved in conidia of M. robertsii Xoch8.1 and B. bassiana Tac1.1. Only one pulse was enough to observe these positive effects on the stress tolerance of the free conidia. However, the Cordyceps genus showed an extreme sensitivity to the treatment, since the quality diminished for Cordyceps fumosorosea ARSEF3302, and in the case of C. javanica CHE-CNRCB303 the treatment affected those tolerance features. In addition, changes in the level of glutathione in the conidia indicated that the treatment could generate oxidative stress, which affects quality. In conclusion, despite the low metabolic activity in free conidia in a latency state, these responded to 26% O 2 pulses, modifying quality traits and in some cases, inducing cross protection in a species-dependent response. The information of this research could be tested in harvested conidia used in the preparation of formulations for biological control.