Eradication, Containment, and/or Management Plum Pox Disease (Sharka)

NON-TECHNICAL SUMMARY: The Plum Pox Virus (PPV) is considered the most economically important stone fruit virus worldwide and it was recently discovered in North America for the first time. This project will determine the distribution of PPV and collect information needed for eradication or effective management of the virus.

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APPROACH: 1. Epidemiological data will be obtained from testing 400 individual trees from infected orchards. These data will be sent to Dr. Tim Gottwald (USDA) for analysis and used to disease incidence. 2. Surveys for PPV will be conducted in weeds and native trees from PPV infested areas using the same DURVIZ PPV ELISA (DASI) test kit procedures of the commercial orchard surveys. New reports of PPV will be confirmed by the USDA/APHIS lab in Beltsville, MD by PCR. These surveys will determine if PPV has crossed over into wild plant populations and increase our understanding of the natural host range of this virus. Aphid transmission experiments will be conducted at the BL3-P facility in Frederick, MD. Results from aphid surveys will be used to develop a list of potential aphid vectors for use in developing future control strategies of vector populations. 3. Economical survey strategies to monitor for the appearance of the virus will be developed such as the use of sentinel plants. New ideas for restricting virus movement will be developed and tested at field stations around the country including ideas for orchard ground cover management to reduce aphid populations and the testing of new aphicidal compounds. 4. Plum Pox eradication / management programs will rely heavily on educational tools. In the event that PPV becomes a management issue traditional and novel delivery systems including grower meetings, extension publications, videos, and the worldwide web will be used to deliver timely information necessary for growers to make informed decisions.
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PROGRESS: 2001/10 TO 2006/09 <BR>
Since the discovery of Plum Pox Virus (PPV) in PA in the autumn of 1999, the goal of state and federal agricultural agencies across the country has been eradication of the virus with a contingency plan of developing management programs should eradication prove impossible. Successful eradication relies on finding and destroying all plants serving as reservoirs of the virus. To this end, several programs have been developed to seek out PPV in potential hosts including commercial orchard, home owner, nursery and native vegetation (weed) surveys as well as surveillance programs using sentinel trees and bait plants. This report summarizes efforts of the weed survey and bait plant surveillance project. Weed collecting sites were generally established adjacent to infected orchards where the potential for virus spread was considered likely. The sites measured one hundred feet by fifty feet and included wooded areas with wild Prunus. These sites served as a reference point so that repeated visits could be made to the same area for collection of plant material. Each year the sites were shifted along the perimeter of the orchard to cover a greater area and prevent repeated sampling of the same perennial weeds. After three years of sampling in one area the sites were moved to different locations based on new findings of PPV infected orchards. Except for grasses and conifers representative samples of all plants were collected and identified to species. A special effort was made to gather samples of weed species that had been cited in the literature as susceptible to PPV. All specimens were tested while they were fresh. The Durviz Plum Pox Virus ELISA kit was used to determine whether any of the samples were infected with virus. Specimens that resulted in suspicious test readings were retested. Specimens that consistently yielded suspicious test readings were sent to the Pennsylvania Department of Agriculture and to the United States Department of Agriculture facilities for confirmation of results. Each year 15,000 - 17,000 samples were processed. A PPV surveillance project was established that used herbacious bait plants to serve as an early detection system for the virus. The host plants, including garden pea, zinnia, clover and African daisy have been reported to become naturally infected with PPV by feeding activities of aphid vectors. Surveillance sites were established on land adjacent to orchards that previously had high levels of PPV infection. Fresh bait plants were germinated in the greenhouse on a weekly schedule. Seedlings were transported to the surveillance sites, maintained for two weeks and returned to the greenhouse for an additional two weeks. This schedule was repeated throughout the summer. Aphids feeding on the bait plants in the field was evidence that this detection system was theoretically sound. Approximately 8,000 bait plants were tested for PPV using the Durviz Plum Pox Virus ELISA kit each year and the results were all negative. In addition to these tests, a number of miscellaneous were also process. Most of these were ornamental plants collected from home owner properties that had been identified as having PPV infected Prunus.
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IMPACT: 2001/10 TO 2006/09 <BR>
Infection with PPV renders many varieties of peaches, plums, nectarines and apricots unmarketable or causes the tree to lose the crop. The potential economic impact on the U.S. stone fruit industry is enormous. Scientific and economic panels have determined that the best course of action for the United States is to eradicate the virus if possible and millions of state and federal dollars have already been invested in the eradication process. Recent PPV survey data shows that the eradication program is effective and eradication of PPV from commercial orchards appears attainable. However, total eradication of PPV will not be accomplished if the virus has managed to become established in native plants that could serve as reservoirs. Determining whether or not natural reservoirs of PPV exist is difficult but the possibility must be addressed. These projects provide important supplemental information to regulatory agencies to show that PPV has not been found in alternate hosts.