Differential Activity of the Extracellular Phenoloxidases in Different Strains of the Phytopathogenic Fungus, Microdochium nivale

To cause plant diseases, phytopathogenic fungi use numerous extracellular enzymes, among which, the phenoloxidases (POs) seem underestimated for the pathogens of non-woody plants. Our study aimed to (1) compare extracellular PO activities (lignin peroxidase, Mn peroxidase, laccase, and tyrosinase) in differentially virulent strains (inhabiting winter rye in a single field) of the phytopathogenic species, Microdochium nivale; (2) check whether these activities are responsive to host plant metabolites; and (3) search for correlations between the activities, lignin-decomposing capacity, and virulence. All strains displayed all four enzymatic activities, but their levels and dynamics depended on the particular strain. The activities displayed the hallmarks of co-regulation and responsiveness to the host plant extract. No relationships between the virulence of strains and levels of their extracellular PO activities or lignin-degrading capacity were revealed. We consider that different strains may rely on different POs for plant colonization, and that different POs contribute to the “uniqueness” of the enzymatic cocktails that are delivered into host plant tissues by different virulent strains of M. nivale. Our study supports the hypothesis of the differential behavior of closely related M. nivale strains, and discusses an important role of POs in the interactions of phytopathogens with herbaceous plants.