RNA mycoviruses and their role in Botrytis biology

Abstract

Mycoviruses are viruses inhabiting and replicating in cells of filamentous fungi, yeasts, and oomycetes. Some mycoviruses can attenuate pathogenicity of their host fungi, thus having the potential for biocontrol of plant fungal diseases. RNA mycoviruses infecting Botrytis were first recorded in 1995. So far, several species of RNA mycoviruses (dsRNA or ssRNA) belonging to Alphaflexiviridae, Gammaflexiviridae, Narnaviridae, Partitiviridae, Totiviridae, and an unassigned viral family have been detected in Botrytis, mostly in B. cinerea. Genomes of a few RNA mycoviruses including B otrytis c inerea m ito v irus 1 (BcMV1), B otryotinia f uckeliana t oti v irus 1 (BfTV1), B otryotinia f uckeliana p artiti v irus 1 (BfPV1), B otrytis c inerea CCg 378 v irus 1 (Bc378V1), B otrytis v irus F (BVF), B otrytis v irus X (BVX) and B otrytis p orri R NA v irus 1 (BpRV1) have been fully or partially sequenced. Three mycoviruses (BcMV1, BVF and BVX) in B. cinerea have a worldwide distribution. BpRV1 was detected in B. porri and B. squamosa. Role of infection of Botrytis by BcMV1, BpRV1 and the 6.8-kb dsRNA mycovirus in attenuation of mycelium growth and pathogenicity of their host fungi has been determined. Vertical transmission of BcMV1 and BpRV1 from hyphae to conidia and horizontal transmission of the two mycoviruses from BcMV1- or BpRV1-infected hypovirulent isolates to virulent isolates of the same and the different VCGs were detected. The combined information suggests that RNA mycoviruses are widespread in Botrytis and some can cause virulence (pathogenicity) attenuation of Botrytis. Further studies on characterization of novel hypovirulence-causing (or hypovirulence-associated) mycoviruses are needed in order to use mycoviruses to control Botrytis.