The psorosis disease of citrus: a pale light at the end of the tunnel

Abstract

First reported in 1896, psorosis was the first citrus disease proven to be graft transmissible and also the first for which eradication and budwood certification programs were launched to prevent its economic damage. For many years psorosis etiology remained elusive, and only in 1986 was the disease associated with the presence of virus-like particles in infected plants. However, in the last 2 decades a virus with unusual morphology (Citrus psorosis virus, CPsV) was characterized and closely associated with psorosis disease as previously defined by field symptoms and by biological indexing in sensitive indicator plants. With a tripartite, negative-sense, RNA genome and a ~48 kDa coat protein, CPsV, the presumed causal agent of psorosis, is the type member of the genus Ophiovirus, within the new family Ophioviridae. Availability of the complete genomic sequence of 2 CPsV isolates and partial sequences of many others has enabled i) setting up rapid and sensitive RNA-based detection methods, ii) testing different citrus and relatives for resistance to CPsV, iii) identification of the 2 components (psorosis A and psorosis B) traditionally associated with non-scaled and scaled bark inoculum, respectively, from psorosis-infected plants and study their interactions, iv) analysis of genetic variation and evolutionary forces shaping the CPsV populations, v) preliminary studies on the interactions between virus and host factors, and vi) development of transgenic citrus plants expressing variable degrees of resistance to CPsV. In summary, 120 years after the first report on psorosis we start seeing a pale light at the end of the tunnel.

Citrus Phantom Disorders of Presumed Virus and Virus-like Origin: What Have We Learned in the Past Twenty Years?

“…Due to the similarity of BBS symptoms with those associated with psorosis, the disease was named Bahia-type psorosis (Nickel et al, 2007). But since CPsV is not its etiological agent, that denomination has been disregarded (Moreno et al, 2015). In 2006, Laranjeira et al suggested that BBS was transmitted by air-borne vectors with limited dispersion ability, strengthening the 6/15 hypothesis of a viral causal agent.…”

Diagnostic Efficiency of CTV and HSVd for Early and Mixed Infections Using Bioamplification in Citrus Arizona 861-S1 and RT‒PCR Compared to Direct RT‒PCR

“…In the case of Chile, citrus exports in 2020 were approximately 365 thousand tons, and constant growth is forecast for the coming years [4]. Citrus graft-transmissible disease (CGTD) is one of the main threats to this industry, causing estimated losses of 15% to 25% within infected orchards [5].…”

Elimination of Citrus psorosis virus using shoot tip grafting and electrotherapy techniques

“…In Egypt, some investigators isolated and identified CPsV (Nour-Eldin, 1956;Nour-Eldin, 1957;Fahmy et al, 2002). Citrus crop losses of graft-transmissible diseases were estimated as much as 15-25% (Moreno et al, 2015). These low losses may be due to the limited spread of the disease in Tucuman (Fawcett and Klotz, 1939).…”