Plum Pox Virus Survey and Eradication Program
Plum Pox Virus, the cause of the most significant and destructive viral disease of Prunus (known as plum pox, PPV, or Sharka) was detected in North America for the first time in 1999. Following recognition of symptomatic peach fruit and the positive confirmation of the causal agent of the disease in October, 1999, an official announcement of the presence of the virus in Adams County, Pennsylvania was made by the Pennsylvania Department of Agriculture. Worldwide, plum pox strains are capable of causing disease in peaches, plums, apricots, nectarines, almonds, sweet and sour cherries, as well as in other selected Prunus and non-Prunus species. The strain of virus found in PA is the D-strain. The virus can be transmitted to healthy plants by more than 20 different aphid species, and spread by movement of infected nursery stock or through grafting.
Upon detection of the Plum Pox Virus in an Adams County orchard in September 1999, the PA Department of Agriculture(PDA) in cooperation with the USDA and Penn State University, teamed up to take the measures necessary to identify, eradicate, and prevent further outbreaks of the Plum Pox Virus.
Damage
In areas of the world where plum pox is established, it is extremely damaging to fruit production. Tree yields can be severely affected - reports claim 80-100% premature fruit drop in some plum varieties. Infected fruit may be unsightly and difficult to sell as table fruit. Export of fruit is difficult; export of budwood and nursery stock is next to impossible.
Distribution
Plum Pox Virus has been described throughout Europe, and in several countries in Asia, Africa, and South America. The virus is well established in many European countries, although it is present only in restricted areas in some western European countries. In North America, the virus has been found and is under eradication in Canada and the United States.
Hosts
Host range depends on virus strain. PPV infects all Prunus species. In Europe, wild Prunus species are reservoirs of the virus, especially Prunus spinosa (blackthorn). Herbaceous plants that have been infected experimentally with PPV include an array of common Pennsylvania weeds, such as white clover (T. repens) and several nightshades (Solanum spp.), although no non-Prunus hosts have been identified in Pennsylvania field surveys.
Symptoms
Symptoms depend on host species and cultivar, and on strain of the virus. Strains are designated D (the strain found in PA), M, C, Rec, Ea, and W. The time between initial infection and symptom expression can vary from one year to several years.
Spread
PPV is transmitted by aphids in a non-persistent manner, and is retained by the aphid for no more than a few hours. The virus is transmitted by several species of aphid common in PA. Aphids do not pass PPV on to their progeny. Seed transmission in Prunus is known NOT to occur with the D strain, but there are some reports of seed transmission with the M strain. Long distance spread is through distribution of infected Prunus budwood and nursery stock.
Diagnostic Tools
Symptoms can be diagnostic, but laboratory testing should back up any diagnosis. Excellent laboratory methods and reagents are available for ELISA and RT-PCR. Bioassay on herbaceous or woody indicators is possible. Distribution of virus in a tree can be irregular, but detection from infected flowers, young leaves, old leaves, fruit, dormant wood, and roots is possible.
Control
The best control is preventing introduction. If introduced, a strict policy of eradication is exercised. In areas where eradication is not an option, less susceptible or tolerant cultivars are used to get fruit yields even when PPV is present. Transgenic plums have been developed that are resistant to PPV.
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