Volatiles emitted by the entomopathogenic fungus Beauveria bassiana elicit growth and defense in sorghum plants

Background Beauveria bassiana is an entomopathogenic fungus that can establish an intimate endophytic relationship with plants. Otherwise, microbial volatile organic compounds (VOCs) are important chemicals for plant recognition and interactions. Therefore, this study provides novel evidence of the biochemical and physiological responses of plants to VOCs emitted by B. bassiana and 3-methylbutanol (3MB) as the most abundant compound emitted by the fungus. Methods Sorghum plants were exposed to the standard 3MB and VOCs emitted by the fungal strains AS5 and AI2 of B. bassiana isolated from soil and a mycosed insect cadaver, respectively. The accumulation of reactive oxygen species (ROS) such as superoxide anion (O 2 • ¯) and H 2 O 2 ; quantification of phytohormones such as salicylic acid (SA), jasmonic acid (JA), and indole-3-acetic acid (IAA) and phenolic compounds in leaves (4-coumaric acid and flavonoids); and the expression of genes SbPR-1 and SbCOI1 related to the activation of SA- and JA-signaling defense pathways, respectively, were analyzed. Results and discussion VOCs emitted by B. bassiana and 3MB stimulate plant growth, likely by triggering the production of ROS and IAA. Furthermore, these fungal compounds increased the expression levels of SbPR-1 and SbCOI1 at 2 d and SbCOI1 at 7 d. Consistently, an increase in the content of SA, JA, and phenolic compounds was observed in the inoculated plants. Conclusion VOCs emitted by B. bassiana and 3-MB promote sorghum growth and activate adaptive defense traits. Moreover, VOCs from AS5 triggered a stronger biochemical response in plants than VOCs emitted by AI2. These results suggested that the response of the plant was strain-specific. Finally, 3MB is a fungal compound that may stimulate plant growth and defense.