A Novel Ilarvirus Is Associated with Privet Necrotic Ringspot Disease in the Southern United States

Abstract

Necrotic ringspot disease (NRSD) is a graft-transmissible disorder of privet (synonym ligustrum), originally reported from Florida and Louisiana more than 50 years ago. In this communication we report an isometric virus isolated from Japanese privet (Ligustrum japonicum) collected in the southern United States displaying symptoms resembling those of NRSD. In mechanical transmission tests, the virus induced systemic infections in several herbaceous hosts. Double-stranded RNA analysis showed a pattern resembling replicative forms of members of the family Bromoviridae. The genome organization along with phylogenetic analyses and serological tests revealed that the virus belongs to subgroup 1 of the genus Ilarvirus. Pairwise comparisons with recognized ilarviruses indicated that the virus is a distinct, and as yet, undescribed member in the taxon, for which we propose the name Privet ringspot virus (PrRSV). Furthermore, the near-perfect association of PrRSV infections with symptoms, and apparent absence of any other virus(es) in studied samples, strongly suggest an important role of this virus in the etiology of NRSD of privet in the southeastern United States.