Preliminary Assessment of Commercial Biofertilizers as Biocontrol Agents of Oak Wilt

Bretziella fagacearum (formerly Ceratocystis fagacearum (Bretz)) Hunt is a vascular pathogen responsible for oak wilt disease, which affects various oak species in North America. Once established, management options include root disruption, removal of infected wood, and fungicide application, each with variable efficacy. This is the first study to assess three commercial biofertilizers against B. fagacearum in vitro, using Spectrum supplemented with Pepzyme Clear (SPC), EM-1, and Power Gelatinase and Chitinase-producing Microorganism (PGCM), as no biological methods currently exist. These biofertilizers were chosen for microbes associated with improved nutrient uptake and for their potential biocontrol activity. We conducted dual-culture plate assays, volatile organic compounds (VOCs) assays, and non-volatile metabolite assays. EM-1 and PGCM exhibited the strongest antagonistic effects for dual-culture plate assays (56% and 68%, respectively) and for VOCs assays (62% and 47%, respectively). After 15 days of exposure to non-volatile metabolites, microscopic analysis revealed severe hyphal distortions from EM-1 and PGCM. These preliminary in vitro findings suggest that PGCM and EM-1 suppressed mycelial growth of B. fagacearum and may be used as biological control. Further field studies are needed to understand how environmental factors and soil-tree-microbe interactions can affect their efficacy against oak wilt disease.