Mycoviruses against plant pathogenic fungi: current understanding and future avenues of their potential implication.

Mycoviruses are ubiquitous and have a wide host range. Their genome characteristics vary greatly among different viral families. Though mycoviruses lack extracellular routes of transmission, they are efficiently maintained in fungal populations through vertical transmission via spores and horizontal transmission through hyphal anastomosis. A subset of mycoviruses induces hypovirulence in plant pathogenic fungi resulting in reduced fungal growth, sporulation and pathogenicity. These Hypovirulence-inducing mycoviruses have potential as biological control agents (BCAs) against fungal diseases, offering an environmentally sustainable alternative to chemical fungicides thereby reducing economic losses in agriculture. However, these biocontrol agents are yet in their preliminary phases. In addition to technical and ecological constraints, certain mycoviruses may negatively affect beneficial fungi that are themselves used as biocontrol agents that raises concerns about unintended impacts. This review provides a brief overview of mycoviruses infecting plant pathogenic fungi, their origin, host range, genome organization, modes of transmission, and effects of mycoviruses on their fungal host, defense mechanisms of mycoviruses and fungi, and methods to detect mycoviruses. Their potential applications as biological control agents have also been discussed along with the challenges faced today. Moreover, limitations of mycovirus-based BCAs have also been briefly discussed here. It will highlight the research gaps as well as the areas that need in-depth research.