Transmission of Furcraea necrotic streak virus (FNSV) by Olpidium virulentus

Abstract

Furcraea necrotic streak virus (FNSV) is the causative agent of necrotic streak disease, also known as macana in fique crops (Furcraea spp.) resulting in damage to leaf fibres and economic losses. The rhizospheric fungus Olpidium spp. is present in the roots of affected plants and may play a role in the disease transmission. FNSV infection and the role of fungi were examined in macanavirus diseased plants in Colombia. Spherical, and icosahedral (24.7 ± 1.98 nm), non-enveloped virions with a granular surface were isolated from field fique plants showing signs of macana disease, and the viral genome was completely sequenced. Taxonomic status was assigned through sequence analysis (Macanavirus genus in Tombusviridae family). The variability of the virus pangenome was evaluated in diseased fique plants from ecologically different Andean regions that showed low gene flow. Olpidium virulentus zoospores, identified by internal transcribed spacer (ITS) sequencing and microscopic analysis, were associated with viral particles and resting spores in diseased fique roots. An in vitro virion?zoospore binding assay showed that FNSV and O. virulentus zoospores interacted. Transmission assays in lettuce (Lactuca sativa), a model plant used to study this virus, showed 100% infection when a preincubated mixture of zoospores and FNSV was added to roots, whereas only 33% infection occurred when FNSV was added alone. This demonstrated the ability of O. virulentus to act as a vector for FNSV, potentially enhancing viral transmissibility in field fique crops. This is the first report of FNSV being transmitted by O. virulentus, a rhizosphere fungus.