Eeva J. Vainio and Jarkko Hantula
from: Viruses of Microorganisms (Edited by: Paul Hyman and Stephen T. Abedon). Caister Academic Press, U.K. (2018) Pages: 193-210.
Fungal viruses (mycoviruses) occur in all major fungal phyla. They are taxonomically highly diverse, and are currently classified into seven families that have mono- or multipartitite dsRNA genomes and six families with ssRNA genomes. One described mycovirus species, Sclerotinia gemycircularvirus 1, has a genome composed of circular ssDNA and resembles plant geminiviruses. Most mycoviruses are considered to form latent infections without major phenotypic alterations in their host fungi, but both detrimental and mutualistic associations are known. As an example, a mycovirus infection causes a disease in cultivated mushrooms resulting in crop losses. On the other hand, hypoviruses of the Chestnut blight fungus (Cryphonectria parasitica) can be used for biocontrol against their host, which is a devastating plant pathogen. There is even one mycovirus involved in a three-way symbiosis formed by a grass, its endophytic fungus, and the virus. Mycoviruses with RNA genomes are considered to be completely intracellular and to transmit laterally between fungal strains during cell-to-cell contact, and vertically via sexual or asexual spores. Most mycovirus species are regarded as host-specific, but there are also examples of horizontal virus transmission between host species. This contradicts the commonly held hypothesis of strict virus-host co-evolution. The evolution of mycoviruses has likely been shaped by events of horizontal transmission between plants and fungi read more ...