Ultrastructure of white-streaked Dendrobium phalaenopsis orchid flowers infected with a rhabdovirus

Abstract

This report describes the first true rhabdovirus in orchids. Virions occurred as long bacilliform particles with a mean length of 320 ± 10 nm and as enveloped bullet-shaped particles and short bacilliform particles with a mean length of 180 ± 10 nm. Semienveloped bullet-shaped particles also were present. Both enveloped and unenveloped particles were in the perinuclear space. Inclusion bodies of similar appearance and density were in the nucleoplasm and the perinuclear space. No virus particles were observed in association with the inclusion bodies in the nucleoplasm but unenveloped virions were found on the margin of the inclusion bodies in the perinuclear space. Perinuclear pockets containing virions were often invaginated into the nucleoplasm or evaginated into the cytoplasm. In contrast to other bacilliform viruses studied in orchids, this virus did not induce the formation of membrane-bounded vesicles lined with unenveloped particles (“spokewheels”) in the cytoplasm. The morphological differences between this virus and other bacilliform viruses found in orchids may represent distinct modes of development of different viruses.