biostudies-literatureShu PWisconsin Potato and Vegetable Growers AssociationUnited States Department of Agriculture- Agriculture Research Service-National Sclerotinia InitiativeUnited States Department of Agriculture Agricultural Research Service National Sclerotinia InitiativeWisconsin Soybean Marketing Boarde1013813https://www.ebi.ac.uk/biostudies/studies/S-EPMC12774355biostudies-literatureUnknown21(12)The mechanisms through which mycoviruses reduce fungal growth and aggressiveness remain unclear, particularly regarding the viral factors involved and their modes of action. In this work, we investigated the hypovirulence mechanism by which Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV1), of the species Gemycircularvirus sclero1, impaired the necrotrophic plant fungus Sclerotinia sclerotiorum growth. We first identified the replication-associated protein (REP) of SsHADV1 as the key factor of hypovirulence. Using different patho-systems, we demonstrated that the viral SsHADV1 REP outside the context of viral infection directly restricts fungal growth and disease development. This slow growth was associated with a reduction in fungal oxalic acid production, which is aPLoS pathogensSclerotinia sclerotiorum growth and aggressiveness are regulated by a mycoviral REP protein.PMC12774355MSN274633MSN2461803060-21220-031-000DAWD00000338Chowdhury RNMajumder KRakotondrafara AMFeng CSmith DLGroves CShu PLawrence AJLasky DTseng YWKnopke-Mooney OMarzano SLKiani YfalseSclerotinia sclerotiorum growth and aggressiveness are regulated by a mycoviral REP protein.The mechanisms through which mycoviruses reduce fungal growth and aggressiveness remain unclear, particularly regarding the viral factors involved and their modes of action. In this work, we investigated the hypovirulence mechanism by which Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV1), of the species Gemycircularvirus sclero1, impaired the necrotrophic plant fungus Sclerotinia sclerotiorum growth. We first identified the replication-associated protein (REP) of SsHADV1 as the key factor of hypovirulence. Using different patho-systems, we demonstrated that the viral SsHADV1 REP outside the context of viral infection directly restricts fungal growth and disease development. This slow growth was associated with a reduction in fungal oxalic acid production, which is a2025-01-01T00:00:00Z2025 Dec2026-06-09T03:18:20.137Z2026-06-09T03:08:02.081ZS-EPMC127743554145291910.1371/journal.ppat.1013813