Metarhizium seed treatment mediates fungal dispersal via roots and induces infections in insects

The study aimed to evaluate the extent to which Metarhizium spp. applied as conidia to seeds will disperse with the growing root system and maintain pathogenicity after dispersion. Tenebrio molitor larvae were exposed to roots of wheat plants that had been grown from seeds inoculated with conidia of either M. brunneum (KVL 04-57 and KVL 12-37) or M. robertsii (ARSEF 2575 and KVL 12-35) in both laboratory and greenhouse settings. All four Metarhizium isolates tested maintained pathogenicity towards T. molitor larvae for up to 4 weeks after being dispersed by roots through both an artificial growth substratum and non-sterile soil. Based on these results we propose that a plant-root association benefits entomopathogenic fungi with mobility in the soil and an increased likelihood of encountering a susceptible insect host.