Archivio Journal of Plant Pathology

Abstract:

A double-stranded RNA (dsRNA) ca. 19 Kbp in size was obtained from tissue extracts of a fig plant (Ficus carica) with chlorotic mottling and vein clearing of the leaves. Leaf dips showed the presence of filamentous closterovirus-like particles with distinct cross banding and a length of about 1800 nm. No virus was recovered by mechanical inoculation to herbaceous hosts. However, virus aggregates were plentiful in thin-sectioned companion cells and differentiating sieve tubes of symptomatic leaves. Using denatured dsRNA preparations as template, a 620 bp cDNA fragment was amplified by RT-PCR using degenerate primers designed on the phosphate motifs 1 and 2 of the heat shock-protein 70 homologue (HSP70h) of members of the family Closteroviridae. Computer-assisted analysis of the sequenced 620 bp fragment showed it to be part of a closteroviral HSP70h gene having identity at the amino acid level with the comparable gene of different closteroviral species ranging from 34% to 48%. In a phylogenetic tree constructed with the amino acid sequences of part of the HSP70h of several members of the family Closteroviridae, the fig virus grouped with species of the genus Closterovirus. RT-PCR with specific primers designed on the HSP70h sequence detected the virus in 36 of 57 field-grown trees, most of which had mosaic symptoms. The present results show that fig hosts a putative closterovirus species for which the name of Fig leaf mottle-associated virus (FLMaV) is proposed.