Soybean blotchy mosaic virus, a new Cytorhabdovirus found in South Africa

Abstract

A previously unidentified plant rhabdovirus associated with a blotchy mosaic symptom of soybean (Glycine max) prevalent in the lower lying, warmer soybean production areas of South Africa, was isolated and partially characterized. The virus was shown to be transmitted by mechanical inoculation and at least one species of leafhopper (Peragallia caboverdensis Lindberg (Cicadellidae, Agalliinae)). To determine the morphology and virion size, as well as intercellular accumulation, negative-stained preparations or embedded ultra-thin sections of infected plant samples were observed under a transmission electron microscope. The distribution of the virions within the cytoplasm, its bullet-shaped morphology and size (338-371nm x 93nm) suggested that it is a putative member of the genus Cytorhabdovirus. Degenerate primers designed to a conserved region of the polymerase gene of a number of rhabdoviruses were used in reverse-transcriptase polymerase chain reaction (RT-PCR) with total RNA from symptomatic plants as template. Amplicons were sequenced and compared to related sequences available on Genbank. The analysis confirmed that the virus was related to cytorhabdoviruses, with the highest nucleotide similarity being 60.7% with Northern cereal mosaic virus. The particle morphology, typical virion accumulation in the cytoplasm of infected cells, nucleotide sequence similarity with that of other plant rhabdoviruses, and unique symptoms on soybeans, suggest that the virus is a previously unknown cytorhabdovirus, for which we propose the name soybean blotchy mosaic virus (SbBMV).