Root colonization of industrial hemp (Cannabis sativa L.) by the endophytic fungi Metarhizium and Pochonia improves growth

Metarhizium is an endophytic, insect pathogenic fungus. Here we investigated the time-course of systemic and rhizospheric colonization by Metarhizium and its influence on the growth of industrial hemp (Cannabis sativa L.). Fungal colonization of hemp root, stem and leaf as well as rhizospheric soil, and agronomic parameters of hemp, were tested in four Metarhizium species with broad- (Metarhizium robertsii, Metarhizium anisopliae, Metarhizium brunneum) and narrow-insect (Metarhizium acridum) host ranges, as well as Pochonia chlamydosporia, a phylogenetically related endophytic fungus that is a nematode pathogen. Root and rhizosphere colonization were found in all Metarhizium species and Pochonia at 10, 20 and 30 days post-inoculation. Pochonia showed greatest root colonization compared to that of all Metarhizium species. Endophytic root colonization by Metarhizium was confirmed by confocal fluorescence microscopy using green fluorescent protein-expressing fungal strains. The genes, cat, mpl and EF1α were tested using a qPCR assay for Metarhizium and hemp. Root colonization by Metarhizium and Pochonia positively influenced shoot length, stem weight and root weight of hemp during the early stages of colonization. Our results suggest the potential for the application of Metarhizium and Pochonia as biocontrol and plant growth promoter agents during hemp colonization.