Not known to transmit any human or animal pathogens.
Not known to vector any pathogens or other associated organisms.
Plum pox virus has been transmitted by at least 20 aphid species, although only a few are considered important vectors. The vectors that are considered important vectors in United States include: the black bean aphid (Aphis fabae), the spirea aphid (Aphis spiraecola), the black peach aphid (Brachycaudus persicae), and the green peach aphid (Myzus persicae).
Approved Method(s)
| Method | Detail | NAPIS Survey Method |
|---|---|---|
| Tissue Sample | Follow National PPV Survey Plan. Also see Sampling PPV document below. | 3011 - General Tissue Sample |
Negative data should be entered into NAPIS at the species level (Potyvirus plumpoxi). New state positive records should be further identified, however, to the strain level. Unusual positive records (highly virulent pathogen, expanded host range, etc.) can be entered at the strain level if strain-level information is available. Please contact stcaps@usda.gov if you need assistance, have questions, or want to enter an unusual record into NAPIS.
Survey Recommendations
No specific signs are present.
Plum pox virus symptoms vary in type and severity with the host, cultivar, environmental and growth conditions, timing of infection, and age of the trees. The virus can also be unevenly distributed within the tree. Healthy branches can be found on infected trees, and healthy and infected buds can occur on the same branch. Newly infected trees can be asymptomatic or symptoms can be restricted to only some parts of the tree, while the development of systemic infection can require several years. Symptoms may appear on leaves, flowers, fruits, stones, and woody tissues.
On leaves, symptoms typically appear in springtime, showing mild light green discoloration, chlorotic spots, bands or rings, vein clearing or yellowing, and leaf distortions.
Flowers can show petal discolorations and malformations with wrinkled petals.
Fruits can show chlorotic spots or lightly pigmented yellow rings. They may become deformed and develop necrotic areas (rings), show internal browning and gummosis of the flesh, and can drop prematurely. Generally, the fruits of early maturing cultivars of all susceptible species show stronger symptoms compared to the late maturing cultivars. In some cultivars, the virus can also cause flattening and cracking on the woody parts of the host. Those cracks develop into large open cankers, and the affected trees may decline over the course of a few years.
See below for symptoms from specific hosts:
Plum: Symptoms on leaves include chlorotic spots, rings and lines. Flowers can show spot necrosis or deformations. Fruits show light halos with darker center and sunken lesions, and stones can have dark spots. They can be deformed and some plum cultivars can drop fruits prematurely.
Peach: Symptoms on leaves include chlorotic spots, rings, bands, and halos. Leaves may be distorted, twisted and banded along the central vein. Lines and spots can appear on the petals, and flowers may exhibit color breaking. Immature fruits can have chlorotic spots and light rings; mature fruits can develop red rings, bright purple-red spots or large halos with a pink center.
Almond: Infection can be symptomless, with some varieties showing resistance. Leaves in infected trees show few symptoms.
Apricot: Symptoms on leaves include mild, pale green rings and diffuse chlorotic spots. Some cultivars show discolored spots with green, red, or violet rings on immature fruits. Fruits may be misshapen, may have rings on the surface of the seed.
Cherry: Symptoms on leaves include discoloration along veins, light green bands, and leaf distortions. Sour cherry fruits can show black ring patterns, depressions, and necrosis, which gradually disappear during ripening. Some sweet cherry fruits develop chlorotic and necrotic rings, notched marks, and premature fruit drop.
See the CAPS datasheet for images of symptoms.
The best time to collect samples is in the spring, from the time new leaves are fully expanded until temperatures become too hot for reliable leaf samples to be collected. Virus antigen levels are significantly lower at 85°F and above. In warmer states, there may be a relatively narrow window in which samples can be collected.
Surveyors should perform visual surveys. Inspect host plants for symptoms and sample symptomatic tissue. Survey for leaves showing symptoms such as mild light green discoloration, chlorotic spots, bands or rings, vein clearing or yellowing, and leaf distortions.
Survey for PPV in apricots, cherry, nectarine, peach or plum trees.
Detection survey for PPV in orchards is based on the use of a hierarchical sampling method. This involves collecting 8 leaf samples from each of 25 percent of the trees in an orchard. Trees to be sampled are selected in groups of 4, with 32 leaves that are collected from the four trees being ELISA tested as four 8 leaf samples. To determine the total number of samples to be collected in an orchard being surveyed, the following formula can be used:
(Number of trees per acre) x (number of acres in the orchard) / 4
Thus, in a 9 acre orchard with a planting rate of 140 trees per acre, 315 eight leaf samples would be submitted for ELISA testing. Sampling at lower rates significantly reduces the likelihood of detecting PPV, and sampling at higher rates is only warranted if there are unusual risk factors present.
Fully expanded symptomatic leaves from the middle of the branch are preferred. However, if symptoms are not present, collect asymptomatic leaves from the same locations. Do not sample dead leaves.
Label the sealed bag with the name of the host (including cultivar) and identification code used in your records in case a positive result triggers additional sampling to confirm a positive PPV tree. Place the sealed plastic bag into a second bag and seal the second bag. DO NOT freeze the plant material. Instead, keep it cool by placing the samples into a cooler with a lid and freezer bags/cold packs.
Approved Method(s)
PPV cannot be visually distinguished from other plant pathogens or abiotic symptoms. Molecular identification is necessary to confirm the presence of PPV. PPV may be confused with Taphrina deformans (peach leaf curl), Apple chlorotic leaf spot and Peach mosaic virus in peach, or Prunus necrotic ringspot in cherry. These diseases are present in the United States.
- EPPO. 2023. Plum pox virus PM 7/32 (2). EPPO Bulletin, 53: 518–539.
- Hughes, G., Gottwald, T.R., and Levy, L. 2002. The use of hierarchical sampling in the surveillance program for Plum pox virus incidence in the United States. Plant Dis. 86:259-263.
- Levy, L., Damsteegt, V., Scorza, R., and Kolber, M. 2000b. Plum pox potyvirus disease of stone fruit. APSnet Feature.
- Mumford, R.A., Perrin, A.S., and Danks, C. 2001. The diagnosis of Plum pox virus in the UK: from strain differentiation to on-site detection. Acta Horticulturae 550: 65-69.
- Rodoni, B., Sarec, R., Mann, R., Moran, J., Merriman, P., Ochoa-Corona, F. and Lovelock, D. 2020. National Diagnostic Protocol for Plum pox virus – NDP2 V4.
- Staniulus, J., Stankiene, J., Sasnauskas, K., and Dargeviciute, A. 1998. First report of sharka disease caused by Plum pox virus in Lithuania. Plant Disease 82(12): 1405.
If you are unable to find a reference, contact STCAPS@usda.gov. See the CAPS Pest Datasheet for all references.