2007 Plum Pox Survey
The Plum Pox Survey will soon be underway!
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2007 Plum Pox Survey
The Plum Pox Survey will soon be underway!
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Sampling of trees and all public outreach will be handled by the New York State Department of Agriculture and Markets. Surveys will be most tightly centered around orchards that had positive trees last summer. Within 500m of tree sites that tested positive, all stone fruit trees will have two samples taken. Out to 1.5 miles from former sites of infection, every second tree will have one sample taken. Beyond this radius, sampling will be random throughout the state. Each sample consists of eight leaves taken from multiple locations on the tree. Distribution of PPV in infected trees is not uniform and this increases the probability that the virus will be detected if present.
Samples will be placed into a plastic bag, bar-code labeled, and stored on ice until delivered to the Experiment Station in Geneva. Once the samples reach Geneva, we will scan them into a database and track them by their barcode number. We will have no information other than the barcode on any sample, so we will not have information as to where samples were taken.
If you have a question about the Plum Pox Survey, you should contact the New York State Department of Agriculture and Markets.
If you suspect that you may have an infected tree, contact your local extension agent as soon as possible.
Plum Pox is a viral disease of stone fruits first reported in Bulgarian plums in 1915. More widely known around the world by its Slavic name, Sharka, the disease first spread slowly through eastern Europe, gaining momentum in the 1950s as it reached Germany, Poland and Russia. In 1970, Plum Pox was reported in France, and in 1986 it was reported in Spain.
Plum Pox is considered the most widespread disease of stone fruits in Europe, with an estimated 100 million trees infected. Movement of the disease has continued, with symptoms first detected in the Western hemisphere in Chile in 1992. Currently, Plum Pox has been detected in North America in Canada and in the United States in Pennsylvania, New York, and Michigan. In New York, Plum Pox was identified on two plum trees in Niagara County in July 2006, followed by a peach tree that tested positive in August of 2006.
Plum Pox follows the convention that viruses are named according to the plant host in which they are first discovered—hence the name Plum Pox Virus (PPV). Plum Pox Virus can infect all cultivated stone fruit species including peach, nectarine, apricot, almond, and cherry, as well as wild and ornamental Prunus and some weed species. Spread of the virus is via aphid vectors and through infected budwood. New York infections are believed to be the result of aphid transfer of the virus from Canada. Four races of PPV have been identified; all occurences in North America thus far have been identified as Race “D”. Race “D” has been shown to naturally infect peach, apricot, plum; almond and sweet and sour cherry are not naturally infected but can be artificially infected by the PPV-D strain. PPV-D is the non-epidemic strain of the virus, as it is not seed-transmitted, is less efficiently aphid-vectored, and is difficult to transmit to experimental hosts.
Newly infected trees are rarely symptomatic. It is critical that symptomless trees be regarded very seriously as they will act as a silent source of further infection. Symptoms of PPV occur sporadically and often are not apparent until three or more years after infection. Symptoms of PPV vary with the strain of the virus, temperature, and by cultivar, age, and nutritional status of the host. The virus may be detectable in some parts of the host but not others. PPV reduces the quality of stone fruit and eventually renders the tree useless for fruit production; even symptomless trees will produce reduced quantities of fruit. All infected trees, even if symptomless, are sources of possible further PPV transmission to other neighboring stone fruit orchard crops.
Leaf symptoms : vein yellowing, light green to yellow rings, may be very subtle
- ( Plum leaves are the most severely affected, with nectoric brown or yellow spots often developing into shot hole.)
-(Peach leaves may show leaf crinkling, puckering, or curling).
-(Apricot leaves show lighter symptoms than peach or plum.)
Flowers : peach varieties with showy blossoms may exhibit color breaking
Fruit : lightly pigmented rings or line patterns resulting from several overlapping rings
-( Apricot and plum fruit may be irregular, deformed, turn brown or become necrotic)
-( and may have rings on the surface of the seed.)
Transmission and Spread of PPV
Short distance spread is the result of nonpersistant aphid transmission. When an aphid test probes a leaf cell, it penetrates the epidermal cell, expels any contents of the stylet into the plant and then draws fresh cell content to taste test the plant. During tasting of an infected host, some of the virus can be pulled into the stylet, stick to the lining of the food canal, and be transferred to a healthy plant. The virus does not persist in the aphid after it has been expelled into new tissue.
Long-distance spread of PPV occurs primarily by movement of infected plants or plant parts. Infection can spread through infected nursery stock or infected buds that are grafted onto healthy trees. Long-distance spread by aphids is unlikely as the lifespan of the virus within an aphid is generally less than an hour.
Exclusion
Commercial growers and nursery propagators should only purchase planting stock that is certified virus-free after it has been tested for PPV and other viruses. Almost universally, intercontinental spread of PPV has been associated with human transfer of infected materials. Therefore, once current, localized US outbreaks of PPV are under control, reliance on regulation and inspection combined with education of importers and travelers will be key in preventing the reintroduction of PPV to the US.
Eradication
The timely elimination of any infected trees found in the US is a critically important control method for PPV. There is no treatment for PPV; once a tree has been confirmed to have PPV it should be removed as quickly as possible to limit spread of the virus to neighboring hosts. If tree stumps are left behind they should be treated with herbicide to avoid sucker shoots, which can also carry PPV. Newly infected orchards are most often detected within 200 yards of an infected host, but can be range up to 1000 yards from the host. Second season infections can be widely scattered from the original infecion site if not controlled. European recommendations are that growers wait three years before replanting to stone fruit after a PPV outbreak.
Insecticides
Aphid control is not a feasible management tool; application of insecticides may reduce the overall population of aphids, but a single aphid can transmit PPV to a new host in a matter of seconds and total control of aphids is impossible to achieve.
Resistance
Limited naturally occuring resistance genes are available for use in developing highly resistant fruit varieties. Currently, the most promising prospect for PPV resistance are genetically engineered resistant stone fruit species. The insertion of PPV genes into plum or apriocot trees confers high resistance or immunity to PPV. This resistance is heritable and can therefore be incorporated into other cultivars through standard breeding practices. Although this method is still in early, experimental stages, it offers hope for the development of commercially viable stone fruit crops that are resistant to PPV.
Detection : Wondering how we find PPV?
Once samples are brought to the lab, we grind them in a buffer solution and test for the presence of PPV using Enzyme Linked ImmunoSorbent Assays (ELISAs). In very simplified terms, a test well is coated with a substance that will adhere to PPV. Each sample is placed in its own well; if PPV is present, it will adhere to the bottom of the well. The wells are then washed with second substance that will stick to PPV, essentially 'sandwiching' the detected virus molecules. The wells are then washed with a color agent that will adhere to the PPV complex. In this fashion, and wells that have PPV in them (from the sample) will develop color; any samples without PPV would not have formed the complex leading up to color adhesion and will therefore not form a color.
Any samples that test positive for PPV will be tested again by ELISA, followed by molecular sequencing techniques to verify the presence of the virus. If these tests are positive, samples will be sent out to two other labs for further confirmation prior to any action being taken.