Bioproducts of Suppress DMI Fungicide-Induced and Gene Expression in and Generate Synergistic Effects with Metconazole and Propiconazole.

Mixtures of fungicides with different modes of action are commonly used as disease and resistance management tools, but little is known of mixtures of natural and synthetic products. In this study, mixtures of metabolites from the rhizobacterium strain ASF009 formulated as Howler EVO with below-label rates (50 µg/ml) of conventional sterol demethylation inhibitor (DMI) fungicides were investigated for control of anthracnose of cherry () caused by . Howler mixed with metconazole or propiconazole synergistically reduced disease severity through lesion growth. Real-time PCR showed that difenoconazole, flutriafol, metconazole, and propiconazole induced the expression of DMI target genes and in . The addition of Howler completely suppressed the DMI fungicide-induced expression of both genes. We hypothesize that the downregulation of DMI fungicide-induced expression of the DMI target genes may, at least in part, explain the synergism observed in detached fruit assays.