Mycoviruses are resident of fungal cytoplasm and have been reported from almost all fungal taxonomic groups. The International Committee for the Taxonomy of Viruses (ICTV) currently recognizes 23 families of mycoviruses, mostly comprising of linear double-stranded RNA (dsRNA), and positive-sense single-stranded RNA ((+) ssRNA). Recently, viruses with single-stranded circular DNA genomes and negative-sense ssRNA ((-) ssRNA) genomes, whether segmented or non-segmented, have also been discovered [1–4]. There number of novel taxa of mycoviruses has been continuously increasing per year. The number and size of genome segments vary among mycoviral families. The nature of mycovirus genomes can vary significantly, and they exhibit a diversity of genetic structures. Each type of mycovirus genome has unique characteristics and replication strategies, contributing to the complexity and adaptability of these viral entities. Mycoviruses having (+) ssRNA genomes are grouped into eight families named Alphaflexiviridae, Barnaviridae, Botourmiaviridae, Deltaflexiviridae, Endornaviridae, Gammaflexiviridae, Hypoviridae, Narnaviridae (https://talk.ictvonline.org/) and the recently proposed family Fusariviridae. Members of the family Fusariviridae have + ssRNA genome ranging from 6 to 10 kb, with the largest ORF encoding a replicase-related protein and one to three smaller ORFs encoding hypothetical proteins with unknown functions. No true capsid has been reported from these viruses [5, 6]. Poly A tail is commonly observed in fusariviruses. Fusarium graminearum virus 1 (FgV1) is an exemplar strain the family Fusariviridae.
Botrytis cinerea is a plant pathogenic fungus which usually infects a wide range of hosts, which includes vegetables, fruits and ornamental plants. Gray mold is a major disease caused by this fungus. Mycelia produced by this fungus is velvety gray in color. Strawberries, raspberries, grapes, kiwis and pears are main host which are infected by this fungus [7]. This fungus is also responsible for postharvest losses. Considering the potential harmful effects of fungicides on humans and animals when used for controlling Botrytis infection, the application of mycovirus biocontrol emerges as a safer and more environmentally friendly approach. In recent years, research on mycoviruses in Botrytis has unveiled a captivating world of viral-fungal interactions that have significant implications for both basic science and applied fields. Mycoviruses have been identified in various species of Botrytis, and their presence appears to be widespread among different geographical regions. The diversity of mycoviruses in Botrytis is characterized by a range of viral families, including A number of mycoviruses have been reported from Botrytis spp., belonging to the families Alphaflexiviridae, Gammaflexiviridae, Endornaviridae, Narnaviridae, Totiviridae and Partativiridae [9, 10] and a recently newly established genus botybirnavirus [11], whilst few are unassigned [9], [12–14]. Among the characterised mycoviruses that infect Botrytis spp., Botrytis cinerea mitovirus 1 (BcMV1 [15, 16], Botrytis cinerea RNA virus 1 [12], Botrytis porri botybirnavirus 1 [11] and Botrytis cinerea CCg378 virus 1 [17] have shown the capacity to attenuate the virulence of host Botrytis. Advances in NGS sequencing technologies have led to a boom in the discovery of many diverse and novel viruses, which have improved our understanding of virus-host interactions. Mycoviruses found in Botrytis have shown promise as potential tools for biological control of fungal diseases. The ability of certain mycoviruses to reduce the virulence of the fungus without affecting its overall fitness raises the possibility of developing mycovirus-based biocontrol strategies for plant protection. Such strategies may offer eco-friendly alternatives to chemical fungicides and contribute to sustainable agricultural practices. However finding a mycovirus with a biocontrol potential is still an ongoing process.
In this study, we report two novel (+)ssRNA mycoviruses isolated from B. cinerea strain Kst14a. Sequence comparisons and phylogenetic analyses of deduced amino acid sequences of their RNA-dependent RNA polymerases (RdRps) revealed that both viruses belong to family Fusariviridae. These viruses were tentatively named Botrytis cinerea fusarivirus 8 (BcFV8) and Botrytis cinerea fusarivirus 9 (BcFV9). Pathogenicity testing and growth comparison analysis showed that both these viruses were responsible for inducing hypovirulence in Botrytis cinerea isolate Kst14a. To our knowledge, this is the first report of fusariviruses co-infecting B. cinerea from Pakistan.