Recent advances in Citrus psorosis virus

Abstract

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.

Keywords: Certification; Citrus psorosis virus; Diagnostics; Ophiovirus; Segmented negative-stranded RNA virus; Viral resistance.

Fig. 1

Symptoms characteristic of the psorosis A (PsA) and psorosis B (PsB) syndromes in field trees in Northeast and Central Morocco (a–d) or in indicator plants in the greenhouse at the index facility at Kenitra, Morocco (e–g). PsA symptoms include bark scaling in the trunk of field trees (a), a shock reaction with leaf shedding of the first flush, and transient chlorotic flecking in young leaves of the following flushes (e) in indicator sweet orange seedlings. PsB symptoms in the field include rampant bark scaling (b–c) and chlorotic blotching in old leaves (d). In indicator sweet orange seedlings PsB isolates incite the shock reaction observed with PsA isolates (e), chlorotic blotches in old leaves (f) with gummy pustules on the underside (g)