Hypovirulence-Based Biocontrol: Mechanisms, Applications, and Prospects for Sustainable Crop Protection

Hypovirulence, defined as a reduction in a pathogen’s capacity to cause disease, can arise naturally or be induced by mycovirus infection, genetic mutation, gene silencing, or other molecular interventions. As an environmentally compatible alternative or complement to chemical pesticides, hypovirulence offers a promising strategy for sustainable crop disease management. A central principle underlying effective hypovirulence-based systems is the balance between attenuation and biological competence: pathogenicity must be sufficiently reduced, while the hypovirulent agent retains the capacity to survive, colonize, persist, or confer protection. Disease suppression can operate through four major, often interacting mechanisms: population-level spread of transmissible hypovirulence determinants, direct impairment of pathogen physiology and virulence traits, activation or priming of host defenses and beneficial endophytic interactions, and competitive exclusion or viral cross-protection. These mechanisms may offer high specificity and reduced non-target impacts, although ecological safety requires system-specific experimental validation; they also provide modes of action distinct from those of conventional pesticides and are suitable for integration into integrated pest management (IPM) programs. This review synthesizes current evidence from fungal, bacterial, and viral pathosystems, explicitly distinguishes laboratory and greenhouse proof-of-concept studies from repeated field evidence, and discusses major biological and operational constraints. We further examine emerging technologies while distinguishing experimentally demonstrated applications from prospective research directions that may improve the reliability, applicability, and scalability of hypovirulence-based biocontrol.