Novel Mycoviruses Discovered in the Mycovirome of a Necrotrophic Fungus

Botrytis cinerea is one of the most important plant-pathogenic fungus. Products based on microorganisms can be used in biocontrol strategies alternative to chemical control, and mycoviruses have been explored as putative biological agents in such approaches. Here, we have explored the mycovirome of B. cinerea isolates from grapevine of Italy and Spain to increase the knowledge about mycoviral diversity and evolution, and to search for new widely distributed mycoviruses that could be active ingredients in biological products to control this hazardous fungus. A total of 248 B. cinerea field isolates were used for our metatranscriptomic study. Ninety-two mycoviruses were identified: 62 new mycoviral species constituting putative novel viral genera and families. Of these mycoviruses, 57 had a positive-sense single-stranded RNA (ssRNA) genome, 19 contained a double-stranded RNA (dsRNA) genome, 15 had a negative-sense ssRNA genome, and 1 contained a single-stranded DNA (ssDNA) genome. In general, ssRNA mycoviruses were widely distributed in all sampled regions, the ssDNA mycovirus was more frequently found in Spain, and dsRNA mycoviruses were scattered in some pools of both countries. Some of the identified mycoviruses belong to clades that have never been found associated with Botrytis species: Botrytis-infecting narnaviruses; alpha-like, umbra-like, and tymo-like ssRNA+ mycoviruses; trisegmented ssRNA− mycovirus; bisegmented and tetrasegmented dsRNA mycoviruses; and finally, an ssDNA mycovirus. Among the results obtained in this massive mycovirus screening, the discovery of novel bisegmented viruses, phylogenetically related to narnaviruses, is remarkable.