First Report of Freesia sneak virus Infecting Lachenalia Cultivars in South Africa

Recent advances in Citrus psorosis virus

Psorosis is a globally devastating disease of citrus caused by an infectious filamentous ophiovirus, Citrus psorosis virus (CPsV), which causes annual losses of about 5 % and a progressive decline of trees by affecting the conductive tissues. The disease can be harboured asymptomatically in many citrus species. In the field, the most characteristic symptoms of the disease in adult trees are bark scaling in the trunk and main branches and also internal staining in the underlying wood. The virus has a tripartite single-stranded RNA genome, and has been inadvertently spread to most citrus growing areas through the movement of citrus propagative material. No natural vectors have been identified except in limited citrus areas in some cases. Management strategies for CPsV involving shoot-tip grafting and thermotherapy or somatic embryogenesis from stigma and style cultures have been successfully used to eliminate CPsV from plant propagating material. Molecular pathogen-mediated strategies have been used to produce citrus plants. Such a strategy protects against infections by the virus from which the resistance gene and promising resistance may emerge from trials. Certification programs are among the best established means of increasing phytosanitary health, and some of those for citrus are among the oldest in the world. In conjunction with quarantine and clean stock programs, they remain important weapons in the ongoing fight against citrus diseases. One of the elements essential for successful certification programs to produce such propagation material is the availability of sensitive and effective diagnostic methods. In this review, we discuss an updated status of CPsV disease.

Ophioviruses CPsV and MiLBVV movement protein is encoded in RNA 2 and interacts with the coat protein

Citrus psorosis virus (CPsV) and Mirafiori lettuce big-vein virus (MiLBVV), members of the Ophioviridae family, have segmented negative-sense single-stranded RNA genomes. To date no reports have described how ophioviruses spread within host plants and/or the proteins involved in this process. Here we show that the 54K protein of CPsV is encoded by RNA 2 and describe its subcellular distribution. Upon transient expression in Nicotiana benthamiana epidermal cells the 54K protein, and also its 54K counterpart protein of MiLBVV, localize to plasmodesmata and enhance GFP cell-to-cell diffusion between cells. Both proteins, but not the coat proteins (CP) of the respective viruses, functionally trans-complement cell-to-cell movement-defective Potato virus X (PVX) and Tobacco mosaic virus (TMV) mutants. The 54K and 54K proteins interact with the virus-specific CP in the cytoplasm, suggesting a potential role of CP in ophiovirus movement. This is the first study characterizing the movement proteins (MP) of ophioviruses.