Biocontrol via mycoviruses: a neglected option for bioprotection?

‘Mycoviruses’ is the term used for viruses infecting fungi and fungus-like
organisms. Mycoviruses have been reported in Ascomycota, Basidiomycota,
Chytridiomycota, Deuteromycota and Zygomycota (Ghabrial et al., 2015). Most
reported mycoviruses consist of linear double-stranded RNA (dsRNA; ~70%),
while a small number are composed of negative single-stranded RNA (−
ssRNA) or positive single-stranded RNA (+ssRNA; ~30%) (Ghabrial et al, 2015;
King et al, 2011). More rarely, mycoviruses with circular single-stranded DNA
(ssDNA) have been found (Jiang et al., 2013; Li et al., 2020; Yu et al., 2010).
Like animal and plant viruses, mycoviruses require the living cells of their host
to replicate. The main differences between animal and plant viruses on the one
hand, and mycoviruses on the other, lie in the fact that most mycoviruses lack an extracellular route for infection and are transmitted between cells through cell division, sporulation and occasionally cell fusion, as well as lacking movement proteins (Son et al., 2015)
Many of these mycoviruses are considered to be cryptic, and supposedly
have little to no effect on their host. However, some notable exceptions have
been described, in which the viruses cause deleterious effects on their host,
and where the host is a plant pathogen, may cause hypovirulence, reducing the
infection, growth and reproduction of the fungus. Virocontrol, the biocontrol
of pathogens via hypovirulence-causing mycoviruses, is a small field, but one
which is now receiving more attention. This chapter discusses the characteristics
of mycoviruses and the conditions that need to be met to make a successful
virocontrol agent. The chapter describes one of the success stories so far, that
of the virocontrol of Cryphonectria parasitica, the chestnut blight pathogen.
The chapter ends by reviewing future trends and information on sources of
more information on mycoviruses and virocontrol.