Metarhizium brunneum (Hypocreales: Clavicipitaceae) and Its Derived Volatile Organic Compounds as Biostimulants of Commercially Valuable Angiosperms and Gymnosperms.

Metarhizium brunneum is a highly effective entomopathogenic fungus that also functions as a plant biostimulant. It can act as both an endophyte and rhizosphere colonizer; however, the mechanisms driving biostimulation are multifactorial. In this work, oilseed rape ( Brassica napus ) seeds were grown in composts treated with different concentrations of M. brunneum strains ARSEF 4556 or V275, or the M. brunneum -derived volatile organic compounds 1-octen-3-ol and 3-octanone. Biostimulation efficacy was found to be strongly dose dependent. Concentrations of 1 × 10 6 conidia g -1 compost were found to be most effective for the M. brunneum , whereas dosages of 1 µL 100 g -1 compost were found to be efficacious for the volatiles. These optimized doses were assessed individually and in combined formulations with a hydrogel against oilseed rape ( Brassica napus ), sitka spruce ( Picea sitchensis ), maize ( Zea mays ) and strawberry ( Fragaria annanassa ). Both volatile compounds were highly effective biostimulants and were found to increase in biostimulatory efficiency when combined with M. brunneum conidia. Hydrogels were not found to interact with the growth process and may offer avenues for novel formulation technologies. This study demonstrates that Metarhizium -derived volatile organic compounds are actively involved in plant growth promotion and have potential for use in novel formulations to increase the growth of a wide range of commercially relevant crops.