Effect of endophytic Beauveria bassiana on herbivore defence in Arabidopsis thaliana

Abstract

The entomopathogenic fungus Beauveria bassiana can live as an endophyte by colonizing plant tissues without causing disease symptoms. Recent studies in different crop plants indicated that endophyte presence can have a negative effect on herbivorous insects. However, whether this was due to induced plant defence responses has not been reported. We established Arabidopsis thaliana as a model plant to find out whether B. bassiana colonization increases herbivore resistance by activating/priming the jasmonic acid (JA) or salicylic acid (SA) defence pathways. Three B. bassiana strains were applied as conidial suspension to Arabidopsis using root dipping. Colonization was assessed through plating on selective medium and through PCR based detection using B. bassiana specific SCAR markers. The endophyte was recovered from leaves and inflorescence confirming systemic colonization throughout the plant. Bioassays were carried out to test the effect of endophyte presence on caterpillars of Plutella xylostella and the aphid Myzus persicae. Endophyte presence did not have any antagonistic effects on the growth of P. xylostella and the fecundity of M. persicae. The re-isolated fungus caused 100% mortality when applied topically on caterpillars. This correlated with the finding that JA levels were only induced by caterpillar feeding but were not influenced by the presence of the fungus. No effect by either treatment was found on endogenous SA levels. In conclusion, our results do not confirm that endophytic B. bassiana induces plant defences against the selected herbivore species. Further studies are planned to assess the plant’s transcriptomic response to the presence of this endophytic entomopathogen.