Antagonism of the endophytic insect pathogenic fungus Metarhizium robertsii against the bean plant pathogen Fusarium solani f. sp. phaseoli

The antagonism of bean (Phaseolus vulgaris) root rot fungus Fusarium solani f. sp. phaseoli by the endophytic insect pathogenic fungus Metarhizium robertsii was investigated in vitro and in vivo. Dual cultures on Petri dishes showed antagonism of M. robertsii against F. solani. A relative inhibition of c. 60% of F. solani growth was observed in these assays. Cell-free culture filtrates of M. robertsii inhibited the germination of F. solani conidia by 83% and the inhibitory metabolite was heat stable. Beans plants colonized by M. robertsii, then exposed to F. solani, showed healthier plant growth and lower disease indices compared with plants not colonized by M. robertsii. These results suggest that the endophytic insect pathogenic fungus M. robertsii could also be utilized as a biocontrol agent against certain plant root pathogens.