''Citrus psorosis ophiovirus'' is a

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

pathogenic

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's 1 ...

infecting

citrus ''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...

plants worldwide. It is considered the most serious and detrimental virus pathogen of these trees.

Psorosis disease

Psorosis includes various graft-transmitted diseases all of which can be associated with different pathogenic strains including the more mild CPs-V-A and more severe CPsV-B. The virus is characterized by a single-stranded RNA molecule with a 48 kDa coat protein and a spiral filament structure. Common hosts of this disease are citrus and herbaceous plants like sweet orange, grapefruit, mandarin, and Mexican lime. Symptoms of infected hosts consist of interveinal chlorotic flecks and leaf mottling in younger tissues–in more severe cases these symptoms persist in older tissues. In mild cases, the bark of the trunk or limbs may exhibit scaling and flaking. Later in the disease cycle, gum can permeate into the wood and form an irregular circular pattern. In more severe cases symptoms include rapid expansion of bark lesions, gum-impregnated lesions on twigs, and chlorotic patterns on fruit. Techniques used for the identification of citrus psorosis virus include the enzyme-linked immunosorbent assay (ELISA) that uses a specific antibody to determine the antigen, polymerase chain reaction to amplify target sequences, and detecting nucleic acids by lateral flow microarrays. Other methods commonly used are direct tissue blot immunoassays, fluorescence in-situ hybridization, immunofluorescence, and electron microscopy for viral pathogen detection. Citrus psorosis virus is often transmitted mechanically by infected budwood or contaminated tools. Additionally, the disease has the potential to proliferate through root grafting or infected seeds. The best management practices that can be implemented involve sourcing indexed and certified disease-free budwood, temporary recovery by pruning infected bark, host removal, and disinfection of machinery or equipment.

Isolation

The Citrus psorosis virus Egyptian strain (CPsV-EG) was isolated from naturally infected citrus grapefruit (''

Citrus paradisi The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit is ...

'' Macf.) at ARC. The grapefruit used for CPsV-EG isolatation was found to be free from CTV, CEVd and ''

Spiroplasma citri ''Spiroplasma citri'' is a bacterium species and the causative agent of Citrus stubborn disease. Its genome has been partially sequenced. The restriction enzyme SciNI, with the cutting site 5' GCGC / 3' CGCG, can be found in ''S. citri''. '' ...

'' by testing with DTBIA, tissue print hybridization and Diene's stain respectively.Ghazal, S.A.; Kh.A. El-Dougdoug; A.A. Mousa; H. Fahmy and A.R. Sofy, 2008. Isolation and identification of ''Citrus psorosis virus'' Egyptian isolate (CPsV-EG). ''Commun. Agric. Appl. Biol. Sci. 73(2): 285–95''. CPsV-EG isolate was transmitted from infected citrus to citrus by syringe and grafting and herbaceous plants by forefinger inoculation and syringe. The woody indicators and rootstocks were differed in response to CPsV-EG isolate which appeared as no-response, response, sensitivity and hypersensitivity. A partial fragment of RNA3 (coat protein gene) of CPsV-EG (–1140bp and –571bp) was amplified by reverse transcription-polymerase chain reaction (RT-PCR) from grapefruit tissues using two sets primers specific CPsV (CPV3 and CPV4) and (PS66 and PS65) respectively. The virus under study was identified as CPsV-EG isolate according to biological, serological and molecular characters. The serological characters represented as the antigenic determinants of CPsV-EG isolate related to monoclonal antibodies specific CPsV strain where as appeared precipitation reaction by DAS-ELISA and DTBIA. CPsV-EG was detected on the basis of biological indexing by graft inoculation which gave oak leaf pattern (OLP) on Dweet tangor and serological assay by DAS-ELISA using Mab specific CPsV. CPsV-EG was reacted with variable responses on 16 host plants belonging to 6 families. Only 8 host plants are susceptible and showed visible external symptoms which appeared as local, systemic and local followed by systemic infections.

Histology

Young grapefruit leaves of both healthy and CPsV-EG infected plants have been studied histologically and ultrastructurally.Sofy, A.R.; A.A. Mousa; H. Fahmy; S.A. Ghazal and Kh.A. El-Dougdoug, 2007. Anatomical and Ultrastructural Changes in Citrus Leaves Infected with ''Citrus psorosis virus'' Egyptian Isolate (CPsV-EG). ''Journal of Applied Sciences Research. 3(6): 485–494''. In general CPsV-EG-infection affects the upper

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...

of the leaf which is composed of non-tabular parenchyma cells covered by a thin layer of

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

. Crystal idioblast (CI) containing cells are lacking in the palisade layer and protrude into the epidermis. The oil glands are lacking compared with healthy leaf. Secondary growth occurs in midvein and major lateral veins in smaller veinlets. The vein endings consist of a single trachoid strand of elongated

parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word π ...

cells enclosed by the bundle sheath compared with healthy ones. The ultrastructure of infected leaves showed a number of changes. Infected cells have large numbers of abnormal

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

and hypertrophied nuclei. Cells of CPsV-EG infected citrus plants have abnormally elongated and curved mitochondria. The nuclei have several dark stained bodies, which are displaced toward nucleus periphery along the nuclear envelope. Sometimes

nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis, which is the synthesis of ribosomes. The nucleolus also participates in the formation of sig ...

appear abnormally shaped. Inclusion bodies that may contain virus particles are also found.

Strains

Three Egyptian isolates of ''Citrus psorosis virus'' (CPsV-EG)—ARC, TB and TN—were obtained from three citrus cultivars—

Grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit is ...

, Balady and

Navel The navel (clinically known as the umbilicus, commonly known as the belly button or tummy button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. All placental mammals have a navel, although ...

—respectively. These isolates were differed in some of their external symptoms. The CPsV-EG isolates were detected by biological indexing, giving rise to Oak Leaf Pattern (OLP) on Dweet tangor. The three isolates were differentiated using Double Antibody Sandwich-Enzyme-Linked Immunosorbent Assay (DAS-ELISA), woody indicator plants, differential hosts, peroxidase isozymes and activity, total RNA content and Reserves Transcription-Polymerase Chain Reaction (RT-PCR). The severe isolate (ARC) gave the highest OD value (2.204) in ELISA, followed by the mild isolate (TB) (1.958) and the last latent isolate (TN) (1.669). These isolates differed also in incubation period, intensity of symptoms and response to sensitivity of woody indicator plants and differential hosts. The CPsV-EG isolates showed differences in isozymes fractions, RF value and intensity as compared with healthy plant. Results were confirmed by peroxidase activity where the level of peroxidase activity was considerably higher in ARC leaves than TB and the last TN. The total RNA content in infected leaves gave the highest content in ARC followed by TB isolate while the lowest was recorded in TN isolate. Finally, RT-PCR showed differences between CPsV-EG isolates of PCR products using specific primer (Ps66 and Ps65) where base number of coat protein gene ARC isolate 571 bp; TB isolate 529 bp and TN isolate 546 bp.El-Dougdoug, Kh.A.; S.A. Ghazal; A.A. Mousa; H. Fahmy and A.R. Sofy, 2009. Differentiation Among Three Egyptian Isolates of ''Citrus psorosis virus''. ''International Journal of Virology. 5(2): 49–63''.

References

{{Taxonbar, from=Q51929876, from2=Q5122915 Viral citrus diseases Aspiviridae