Almond; Apricot; Peach, Nectarine; Plum

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 the northeastern United States include: the black bean aphid (Aphid fabae), the spirea aphid (Aphid spiraecol), the black peach aphid (Brachycaudus persicae), and the green peach aphid (Myzus persicae).

Negative data should be entered into NAPIS at the species level (Potyvirus Plum pox virus). 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 Cynthia Music or Daniel Mackesy if you need assistance, have questions, or want to enter an unusual record into NAPIS.

No specific signs are present.

Symptoms of PPV can be conspicuous or very subtle on stone fruit trees. Symptoms vary in type and severity with the strain of the virus, host, cultivar, environmental factors, and the timing of infection. Diagnostic symptoms occur mainly on leaves and fruits in the United States. In general, leaf symptoms include vein yellowing or light green to yellow rings. Foliar symptoms may develop during the cooler temperatures of spring and fall but fade during the hot summer months. Symptoms of PPV occur sporadically and often are not apparent until three or more years after infection. Newly infected trees are rarely symptomatic.

Plums: Pale green or light yellow chlorotic spots, blotches, bands, rings, or line patterns may occur on the leaves. They are difficult to see in the bright sunlight. Leaf symptoms are most easily seen on the fully expanded leaves from late May/early June. These symptoms are often irregularly distributed and may appear on only a few branches or leaves. Plum fruit symptoms depend on the original color of the fruit. Dark-skinned fruits show bluish, necrotic rings, which may be sunken. Pale-skinned fruit show uneven ripening, blotching, and rings. Necrotic tissue may extend through the flesh to the stone, on which a reddish necrotic ring may develop. Plum fruits are often deformed. Also, some plum cultivars can drop fruit prematurely.

Peach: The leaf symptoms of PPV on peach are distinctive. Affected leaves are distorted when they first unfold, having a wavy edge and a slight twist, and the veins show pale green or bright yellow flecks or lines. These symptoms disappear as the leaves mature. Peach fruit may develop lightly pigmented rings or line patterns that result from the convergence of several rings. Peach fruit, however, may have paler colored rings and lines than those found in plums. Peaches are generally more susceptible to damage from the disease than plums. Flowers on PPV-infected peach trees may exhibit color breaking but only on cultivars with large showy flowers. Color-breaking appears as darker pink stripes on the flower petals.

Apricot: Show lighter symptoms than plum or peach. Apricot fruits may be misshapen, turn brown or become necrotic and may have rings on the surface of the seed.

Almonds: Show few leaf symptoms. Infection is often symptomless.

Cherry: Pale green patterns and rings appear on the leaves. Fruits are slightly deformed with chlorotic and necrotic rings, notched marks, and premature fruit drop.
Note: PPV strain D, which occurs in the United States, is not known to naturally cause infection in cherry.

The visual symptoms accompanying the reduction in sugar content make the affected fruit unmarketable.

A diagram for optimal leaf sampling of stone fruit trees can be found here.

The approved screening protocol for the field is the PPV Enzyme-Linked ImmunoSorbent Assay (ELISA). The work instruction is available upon request. The work instruction describes detection of PPV using the ELISA kit from Agdia Inc., which detects six known PPV strains/subgroups: PPV-C, PPV-D, PPV-EA, PPV-M, PPV-Rec, and PPV-W in leaves, fruit, and flowers.

PPV symptoms are sometimes difficult to distinguish from other diseases and may be confused with rusty spot (Podosphaera spp.) of peaches and nectarines and bacterial canker as well as insect-related problems such as damage from thrips, white apple leafhopper, and San Jose scale. Nutritional deficiencies and pesticide damage can also be confused with PPV symptoms.

In the United States, the disease was recorded in Pennsylvania in 1999 followed by New York and Michigan in 2006. The disease has since been eradicated in Michigan and Pennsylvania. Eradication efforts are continuing in New York (Levy et al., 2000).

Eight strains of PPV (D, M, El-Amar, C, W, T, CR, and Rec) have been identified worldwide based on their biological, serological and molecular properties to date. PPV-M and PPV-D are the most widespread. All occurrences in the United States have been identified as strain D (PPV-D).