A Novel Naturally Occurring DNA Virus with Significant Potential for Controlling Sclerotinia sclerotiorum

Although mycovirus-based biopesticides have shown promise in laboratory studies, they are not yet widely available. Our previous characterization of soybean leaf-associated gemygorvirus 1 (SlaGemV1) indicated its unique property for extracellular transmission and to evaluate its effectiveness against Sclerotinia sclerotiorum, we tested three formulations in greenhouse and field settings. First, in greenhouse trials, introducing hypovirulent S. sclerotiorum infected with SlaGemV1 into soil at the time of planting led to significant improvements in leaf area, plant height, and photosynthetic efficiency (all P < 0.01) while also reducing disease symptoms from subsequent S. sclerotiorum infections (P < 0.001). In field tests, plant height increased (P < 0.01). Second, SlaGemV1-infected S. sclerotiorum was homogenized to create a slurry, which was sprayed at flowering. This treatment provided protection against S. sclerotiorum infection, reducing sclerotia formation and average lesion lengths on greenhouse tomato plants (P < 0.05) and reducing lesions on pinto bean plants (P < 0.01) while increasing aboveground dry mass under S. sclerotiorum inoculation (P < 0.05). Third, filtering the homogenate and spraying crude particle filtrates (PFs) successfully reduced lesion lengths in basil, geranium, and sunflower (P < 0.05) in greenhouse trials. In 2023, PF spray also lowered disease incidence in sunflower plots in the field (P < 0.05). In 2024, PF-treated soybean and sunflower plots showed a significantly reduced disease severity index at the end of the growing season (P < 0.05). Based on these findings, we conclude that SlaGemV1 is an effective biopesticide using the formulations and delivery methods described.