Psorosis

Background
Psorosis is a serious and widespread disease that affects citrus trees. It is one of the oldest citrus diseases: the name psorosis has been used since the late nineteenth century to describe certain characteristic citrus damages. The first documents which provide experimental evidences referred to the appearance of the disease were written by Fawcett .Psorosis has been reported in many countries around the world. However it has been confirmed only in North and South America and in the Mediterranean basin.

Symptoms
Typical symptoms of psorosis are bark scaling (which gives origin to the name psorosis), with pustules and accumulation of gum on the trunk; flecking, clorotic spots, and necrotic shock, on leafs. Two types of psorosis have been described : Psorosis A and B. The second is stronger than the first. The appearance of these kinds of damage is very slow: it can appear 10 to 15 years after infection, and for that reason the analysis of disease progression becomes very difficult. Citrus plants affected with psorosis are less productive; therefore this disease causes economic loss.

Causal agent
This plant pathology is caused by a virus called Citrus psorosis virus (CPsV), which is part of the genus Opfiovirus, within the recently described family Ophiovirae. The virus has a wide host range, mainly sweet orange (Citrus sinensis (L.) Osb.), mandarin (C. reticulata Blanco) and grapefruit (C. paradisi Macf.). Other species such as sour orange (C. aurantium L.), lemon (C. limon (L.) Burn. F.), rough lemon (C. jambhiri Lush) and pummelo (C. grandis (L.) Osb., can harbor CPsV, but they do not show symptoms).This virus can also infect herbaceous plants like Chenopodium quinoa, Nicotiana benthamiana and Gomphrena globosa. They are used as herbaceous experimental models.