View source for Plum pox

{{Taxobox_begin | color = violet | name = ''Plum pox virus''}}
{{Taxobox image | image =[[Image:Ppv2.gif|240px| Genome organisation of Plum pox potyvirus]] | caption = Genome of PPV with proteolytic cleavage sites}}
{{Taxobox_begin_placement_virus}}
{{Taxobox_group_iv_entry}}
{{Taxobox_familia_entry | taxon = [[Potyviridae]]}}
{{Taxobox_genus_entry | taxon = '''''[[Potyvirus]]'''''}}
{{Taxobox_species_entry | taxon = '''Plum pox virus'''}}
{{Taxobox_end_placement}}
{{Taxobox_end}}

'''Plum pox''', also known as '''sharka''', is the most devastating viral disease of [[stone fruit]] from the genus ''[[Prunus]]''. The disease is caused by the '''plum pox [[virus]]''' (PPV), and the different strains may infect a variety of stone fruit species including [[peach]]es, [[apricot]]s, [[plum]]s, [[nectarine]], [[almond]]s, and [[Wild Cherry|sweet]] and [[Morello Cherry|tart]] [[cherry|cherries]]. Wild and ornamental species of ''Prunus'' may also become infected by some strains of the virus. 

The virus is transmitted by [[aphid]]s and by the transfer of infected plant material to new locations. Plum pox poses no danger to consumers. But it can ruin the marketability of stone fruit by causing acidity and deformities. The only way to manage the disease is to destroy all infected trees, which can cause significant economic losses. A [[transgenic plant|genetically modified]] plum resistant to plum pox virus has been developed but is not commercially available.

==Biology==
The plum pox virus is a linear single stranded [[RNA]] virus.<ref name="ictvdb">International Committee on the Taxonomy of Viruses. 2002. [http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/57010054.htm Plum pox virus]<br></ref> There are four strains of plum pox virus: PPV-D, PPV-M, PPV-EA, and PPV-C. PPV-M isolates are more aggressive in peach, are [[aphid]] [[vector (biology)|vector]]ed more efficiently, and spread more rapidly in an orchard.<ref name="aphis">APHIS. [http://www.aphis.usda.gov/ppq/plumpox/faqs.html Plum Pox Potyvirus Disease of Stone Fruits]<br></ref> PPV-M has been reported to be [[seed]] transmitted, the other PPV strains are known not be transmitted through seeds. Both PPV strains M and D infest peach, plum, and apricot. PPV-C infects [[Wild Cherry|sweet]] and [[Morello Cherry|tart]] cherry naturally and is the only strain known to do so, it has infected other ''Prunus'' hosts experimentally.

==Pathology==
[[Image:Myzus persicae.jpg|right|thumb|140px|The aphid ''Myzus persicae'' is a vector for plum pox virus in the United States.]]

Several aphid species can transmit plum pox within an orchard and over short distances (200-300 meters) to trees in nearby [[orchard]]s. Unlike some other viruses, like [[barley yellow dwarf virus]], PPV is not persistent in the aphid and is transferred from the mouthparts of the aphid between plants. Long distance spread usually occurs as a result of the movement of infected nursery stock or propagative materials. Once a plant is infected the virus is systemic and occurs in the [[cytoplasm]] of [[cell (biology)|cell]]s from all parts of the plant.

When a host tree is infected by plum pox, the infection eventually results in severely reduced fruit production, and the fruit that is produced is often misshapen and blemished. The presence of plum pox can also enhance the effects of other endemic viruses infecting various species of the genus ''Prunus'', such as prune dwarf virus, Prunus necrotic (browning) ringspot virus, and apple chlorotic (yellowing) leaf spot virus, resulting in still greater economic losses.
[[Image:Plum pox in apricot.jpg|240px|left|thumb|Plum pox infection in an apricot. There are rings on the leaves and the fruit and seed are discoloured.]]
In [[peach]], infected trees may exhibit color-breaking symptoms in the [[blossom]]s. This appears as darker pink stripes on the flower [[petal]]s and can be useful for early season surveys. Symptoms can be present in young leaves in the spring and /or on developing [[fruit]]. Some trees show no symptoms on leaves or fruit. 

Not all infection in ''Prunus'' are characterized by a ring symptom on leaves. Several cultivars show yellowing line patterns and blotches, or necrotic ring symptoms on expanded leaves. Leaf distortion has also been observed. Infected fruit can develop yellow rings or blotches, or brown rings, and some [[plum]] and [[apricot]] fruit can be severely deformed and bumpy. The seed of many infected apricots and some plums show rings.

Many non-''Prunus'' species, in at least nine plant families, have been infected artificially with one or more strains of the plum pox virus, and in some cases found naturally infected in the field. The manintance of the virus in non-''Prunus'' species complicates disease management.

==Management==
[[Image:C5 plum pox resistant plum.jpg|right|thumb|200px|C5 genetically modified plum pox resistant plum (''Prunus domestica)''.]]
There is no cure or treatment for the disease once a tree becomes infected. Infected trees must be destroyed. Once the disease becomes established, control and prevention measures for plum pox include field surveys, use of certified nursery materials, control of aphids, and elimination of infected trees in nurseries and orchards. 

Sources of resistance exist in ''Prunus'', but are not common. A team of scientists from the [[United States]] and [[France]] has [[genetic modification|genetically engineered]] a plum pox-resistant plum called C5, and the resistance can be transferred through hybridization to other plum trees. The [[transgenic plant|transgenic]] plum expresses a plum pox virus coat protein, the plant produces the coat protein [[mRNA]] and it is processed by a system called [[post transcriptional gene silencing]] (PTGS), which functions like  the plants immune system and is mechanistically similar to [[RNAi]].<ref name="hily2004">Hily, J.M. et al. 2004. Stability of gene silencing-based resistance to Plum pox virus in transgenic plum (''Prunus domestica'' L.) under field conditions. ''Transgenic Research'' 13: 427-436<br></ref> C5 provides a unique source of [[germplasm]] for future breeding programs worldwide. Similar success has not yet occurred in attempt to genetically modify other ''Prunus'' species, although these efforts are ongoing.

==Distribution==
{|border="2" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; border: 1px #aaa solid; border-collapse: collapse;"
|- bgcolor="#d3d3d3"
!width="150"|Disease Status
!Country
|-
|Restricted Distribution
|[[Albania]], [[Austria]], [[Canada]], [[Cyprus]], [[Czech Republic]], [[France]], [[Italy]], [[Luxembourg]],[[Moldova]], [[Norway]], [[Portugal]], Southern [[Russia]], [[Slovenia]], [[Spain]], [[Syria]], [[Turkey]], [[Ukraine]], [[United Kingdom]], [[United States]]
|-
|Widespread
|[[Bulgaria]], [[Croatia]], [[Germany]], [[Greece]], [[Hungary]], [[Poland]], [[Romania]], [[Slovakia]]
|-
|Introduced, Established
|[[Azores]], [[Bosnia-Herzegovina]], [[Egypt]], Former USSR including [[Central Asia]], [[India]], [[Lithuania]]
|-
|Introduced, Presumably Eradicated
|[[Belgium]], [[Netherlands]], [[Switzerland]]
|-
|Present Status Unknown
|[[Chile]], [[Denmark]]
|-
|colspan="2"| <small>Modified from: Levy et al. 2000. Plum Pox Potyvirus Disease of Stone Fruits. American Phytopathological Society<ref name="levy2000">Levy et al. 2000. [http://www.apsnet.org/online/feature/PlumPox/ Plum Pox Potyvirus Disease of Stone Fruits]. American Phytopathological Society<br></ref><small>
|}
	
In the fall of 1999, plum pox strain PPV-D was detected in an [[Adams County, Pennsylvania|Adams County]], [[Pennsylvania]] orchard. This was the first time that plum pox had been found in [[North America]]. The infected areas in Pennsylvania have been quarantined to prevent the spread of the disease, and infected trees have been destroyed.<ref name="aphis" /> 

Since this time, as a result of random surveying done in 2000, detection has also occurred in [[Nova Scotia]] and in Southern Ontario, particularly in the [[Niagara Region]]. Like the United States infection, the [[Canadian Food Inspection Agency]] has put into effect quarantine zones throughout Southern Ontario in a bid to prevent the spread of PPV. The virus has yet to be found in other areas of Canada which contain susceptible trees despite intense surveying. The Canadian plum pox eradication initiative has involved large numbers of samples tested for the plum pox virus. Samples are tested through a technology known as enzyme linked immunosorbent assay (ELISA). The University of Guelph - Laboratory Services Division has performed well over 2,000,000 tests in the past 5 years in support of this initiative.

==References==
{{reflist|2}}
<!-- dead reference:
{{mnb|CFIA|5}}Canadian Food Inspection Agency - Plant Protection Division [http://www.inspection.gc.ca/english/plaveg/pestrava/ppv/contexte.shtml Canadian Context of PPV]
[http://www.plumpox.blogspot.com University of Guelph PPV Laboratory]
-->

[[Category:Plant pathogens and diseases]]
[[Category:Viruses]]

[[cs:Šárka (nemoc)]]
[[de:Grüne Pfirsichblattlaus]]
[[fr:Sharka]] 
[[it:Sharka]]
[[nl:Groene perzikluis]]
[[pt:Myzus persicae]]