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Abstract
Citrus psorosis was reported for the first time in Florida in 1896 and was confirmed as a graft-transmissible disease in 1934. Citrus psorosis virus (CPsV) is the presumed causal agent of this disease. It is considered as a type species of the genus Ophiovirus, within the family Aspiviridae. CPsV genome is a negative single-stranded RNA (-ssRNA) with three segments. It has a coat protein (CP) of 48 kDa and its particles are non-enveloped with naked filamentous nucleocapsids existing as either circular open structures or collapsed pseudo-linear forms. Numerous rapid and sensitive immuno-enzymatic and molecular-based detection methods specific to CPsV are available. CPsV occurrence in key citrus growing regions across the world has been spurred the establishment of the earliest eradication and virus-free budwood programs. Despite these efforts, CPsV remains a common and serious challenge in several countries and causes a range of symptoms depending on the isolate, the cultivar, and the environment. CPsV can be transmitted mechanically to some herbaceous hosts and back to citrus. Although CPsV was confirmed to be seedborne, the seed transmission is not efficient. CPsV natural spread has been increasing based on both CPsV surveys detection and specific CPsV symptoms monitoring. However, trials to ensure its transmission by a soil-inhabiting fungus and one aphid species have been unsuccessful. Psorosis disease control is achieved using CPsV-free buds for new plantations, launching budwood certification and indexing programs, and establishing a quarantine system for the introduction of new varieties. The use of natural resistance to control CPsV is very challenging. Transgenic resistance to at least some CPsV isolates is now possible in at least some sweet orange varieties and constitutes a promising biotechnological alternative to control CPsV. This paper provides an overview of the most remarkable achievements in CPsV research that could improve the understanding of the disease and lead the development of better control strategies.
Highlights
Psorosis is a widespread citrus disease in the world, causing yield, growth, and longevity reduction of infected trees which may linger for a few years before dying out [1]
Single-strand conformation polymorphism (SSCP) analysis of the RNA2 population occurring within different tissues of psorosis-infected plants showed that: (i) psorosis A (PsA)-inducing isolates accumulate in all tissues and contain psorosis B (PsB)-associated sequence variants at low frequency; (ii) the PsB-associated sequence variant is prevalent in blistered twigs and gummy pustules produced in old leaves, characteristic of PsB isolates; and (iii) the PsB-associated sequence variant shows a preference for accumulating in bark lesions of the trunk and limbs [23]
The results effectively showed that an Olpidium-like fungus is associated with citrus roots and that Citrus psorosis virus (CPsV) is detectable in zoospores from infected roots
Summary
Psorosis is a widespread citrus disease in the world, causing yield, growth, and longevity reduction of infected trees which may linger for a few years before dying out [1]. SSCP analysis of the RNA2 population occurring within different tissues of psorosis-infected plants showed that: (i) PsA-inducing isolates accumulate in all tissues and contain PsB-associated sequence variants at low frequency; (ii) the PsB-associated sequence variant is prevalent in blistered twigs and gummy pustules produced in old leaves, characteristic of PsB isolates; and (iii) the PsB-associated sequence variant shows a preference for accumulating in bark lesions of the trunk and limbs [23] Overall, these results agree with those of previous studies suggesting that different CPsV isolates may be involved in citrus psorosis and ringspot diseases [43,44]. This statement corroborates the idea that citrus psorosis remains a graft-transmissible disease that represents a major concern for citrus growers in the country due to its particular and poorly understood dissemination means [5]
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