Molecular characterization of a novel botoulivirus from the phytopathogenic fungus Sclerotinia minor

The good, the bad and the cryptic: The multifaceted roles of mycoviruses and their potential applications for a sustainable agriculture

Mycoviruses are natural inhabitants of fungi and have been identified in almost all fungal taxonomic groups. Mycoviruses that infect phytopathogenic fungi are now becoming a hot research area due to their potential for the biocontrol of important plant pathogens. But, before considering a mycovirus for biocontrol, we should be fully aware of the effects it induces in a fungal host and its interactions with other viruses, fungal strains and even the host plants. Mycoviral infections are generally associated with different effects, ranging from hypovirulence to hypervirulence, but they can often be cryptic (latent infections). The cryptic lifestyle has been associated to many mycoviruses, but thanks to growing knowledge we are now aware that it is often associated to axenic conditions while the real effects can be observed only in nature. Other mycoviruses either promote (hypervirulence) or (hypovirulence) fungal pathogenicity by a strong impact on the fungal physiology or by blocking the production of toxins or effectors. Finally, indirect effects of mycoviral infections can also be provided to the plant that hosts the fungal isolate, highlighting not only their potential as direct biocontrol agents but also as priming agents for plant resilience to biotic and abiotic stresses. This review provides a broad overview of mycoviral interactions both with their hosts and with other mycoviruses, highlighting the most interesting examples. In contrast to what has been observed to date, we believe that the collective availability of these data will not only improve our understanding of mycoviruses, but also increase our confidence in considering them as alternative measures against fungal diseases to improve the sustainable production of food and feed commodities.

Multiple mycoviruses identified in Pestalotiopsis spp. from Chinese bayberry

Background

Chinese bayberry (Myrica rubra) is a subtropical fruit crop widely grown in southern China. Twig dieback is a disease of Chinese bayberry caused by Pestalotiopsis spp. and results in great economic losses to Chinese bayberry production. A virus survey was conducted in the population of Pestalotiopsis spp. infecting M. rubra in China. We explored the viral diversity in Pestalotiopsis spp., which may provide resources for further development as biocontrol agents of twig dieback.

Methods

Strains of Pestalotiopsis spp. were isolated from diseased twigs of M. rubra, and cultured on potato dextrose agar for RNA extraction. The total RNA of each strain was extracted, mixed, and used for RNA sequencing. The resulting sequences were deduplicated, annotated, and then used for phylogenetic analysis.

Results

Seven novel viruses were characterized from 59 isolates of M. rubra collected from 14 localities in China. Based on the phylogenetic analysis, these viruses were classified into five viral families/orders, Botourmiaviridae, Mitoviridae, Partitiviridae, Tymovirales and Bunyavirales, and one virus, Pestalotiopsis negative-stranded RNA virus 1, which likely belongs to a new viral family.

Conclusions

Metatranscriptomics analysis showed the presence of various mycoviruses in Pestalotiopsis spp. isolated from M. rubra in China. The genomes of eight putative viruses were identified, seven of which were nearly full-length. Some of these viruses of Pestalotiopsis spp. may have the potential for the biological control of twig dieback of M. rubra.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01513-3.