Characterization of two plant rhabdoviruses not previously reported in South Africa

Abstract

Two previously uncharacterized plant rhabdoviruses, infecting Bermuda grass (Cynodon dactylon (L.) Pers) and soybean (Glycine max) respectively, have been found in South Africa. To determine the morphology and virion size of these viruses, embedded ultra-thin sections of infected plant samples were observed under a transmission electron microscope. The virion distribution within the cell, the bulletshaped morphology and the virion sizes indicated that both these viruses might belong to the Rhabdoviridae family. Degenerate polymerase chain reaction (PCR) primers were designed by alignment of the polymerase gene sequences of several plant rhabdoviruses in order to identify conserved regions. Standard PCR and sequencing protocols were used to determine a partial polymerase gene sequence of the viruses that was then compared to the most closely related sequences available on Genbank. The analysis indicated that the Cynodon rhabdovirus was most closely related to known nucleorhabdoviruses; and the rhabdovirus-infecting soybean (Soybean blotching mosaic virus proposed name) was closely related to other known cytorhabdoviruses. These results indicate that both the viruses are new members to the Nucleo- and Cytorhabdovirus genera, respectively.