Progress 10/01/01 to 09/30/06
Outputs
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.
Impacts
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.
Publications
- No publications reported this period
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Progress 01/01/05 to 12/31/05
Outputs
The PPV eradication program appears to be making excellent progress but the virus has not yet been eliminated from the quarantine zone. In 2005 the virus was found in three orchards that were in close proximity to each other and not scattered throughout the quarantine zone as might be expected. The pattern of infection is suggestive of a local unknown reservoir. To follow up on this possibility, weed collecting sites have been established in the woodlands and undisturbed marginal areas around these infected orchards to test the weed populations. Similarly, new weed collecting sites were established in 2004 around an infected two-year-old fruit tree nursery that was located approximately seven miles from the nearest known virus source. It is not possible to know the significance of these pockets of infection. Ideally they may be the last remnants of PPV in the quarantine zone although they could also be indicators of undetected PPV reservoirs. Therefore, it seems
prudent to follow up on weed surveys in these locations to check if wild plants are infected. Two different programs have been developed to search for reservoirs of PPV. The protocol for each program has been described in earlier reports. The Weed Survey tests for PPV in indigenous weeds and native trees within the PPV quarantine zone. A total of 15,307 samples from 86 different weed and native tree species were tested and all were negative for PPV. The Surveillance Project uses herbacious bait plants as an early detection system for PPV. Seedlings of known herbaceous hosts for PPV were transported to field locations where aphid vectors were allowed to feed on them for two weeks. The plants were then returned to the greenhouse for an additional two weeks before testing by ELISA. This schedule was repeated throughout the summer. Two of the surveillance sites that were used in 2004 were taken down and reestablished in the vicinity of three new infection sites discovered early in 2005.
In 2005 a total of 8,688 bait plants were processed and all were negative for PPV.
Impacts
Millions of state and federal dollars have been spent on PPV eradication. The data from commercial orchard, home owner, weed, bait plant and sentinel tree surveys indicate that the eradication program is working and success appears to be at hand. It is critical however, that all reservoirs of PPV be identified and destroyed or a resurgence of the virus is likely. For both practical and financial reasons it is imperative that eradication be completely successful because a second opportunity may not be possible. The weed survey and bait plant surveillance projects are designed to provide important supplemental information to regulatory agencies to show that PPV has not been found in alternate hosts.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
The number of commercial fruit trees testing positive for PPV has declined dramatically over the past few years which supports the idea that eradication of PPV is possible. However the possibility that unknown reservoirs of PPV exist in wild Prunus or other native plants continues to be a major concern. In 2003 PPV was found for the first time in an ornamental Prunus and in 2-year-old nursery trees with no known nearby source of inoculum suggesting that reservoirs may exist. Two different programs have been developed to search for reservoirs of PPV. The protocol for each program has been described in earlier reports. The "Weed Survey" tests for PPV in indigenous weeds and native trees within the PPV quarantine zone. In 2004 the weed collecting sites were shifted to new locations to broaden the search and to minimize repeated sampling of the same perennial weeds each year. In addition, a new site was established in the vicinity of the PPV infected nursery block. A
total of 15,058 samples from 115 different plant species were tested and all were negative for PPV. The "Surveillance Project" uses herbacious bait plants as an early detection system for PPV. Seedlings of known herbaceous hosts for PPV were transported to field locations where aphid vectors were allowed to feed on them for two weeks. The plants were then returned to the greenhouse for an additional two weeks before testing by ELISA. This schedule was repeated throughout the summer. The same surveillance sites that were maintained in 2003 were used in 2004 as well as three new sites that were set up in the vicinity of the infected tree nursery. In 2004 a total of 8,384 bait plants were processed and all were negative for PPV.
Impacts
Millions of state and federal dollars have been spent on PPV eradication. The data from commercial orchard, home owner, weed, bait plant and sentinel tree surveys indicate that the eradication program is working and success appears to be at hand. It is critical however, that all reservoirs of PPV be identified and destroyed or a resurgence of the virus is likely. For both practical and financial reasons it is imperative that eradication be completely successful because a second opportunity may not be possible. The weed survey and bait plant surveillance projects are designed to provide important supplemental information to regulatory agencies to show that PPV has not been found in alternate hosts.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Two projects designed to monitor for Plum Pox Virus (PPV) within Pennsylvania's PPV quarantine zone were continued in 2003. The 'weed survey' protocol remained essentially the same since the project was initiated in 2000 and details can be found in an earlier report. Collecting sites that had been used for three consecutive years were discontinued and replaced by new sites. Close proximity to PPV infected orchards remained the primary criterion for site selection. Leaf samples from weeds and native trees were collected two to three times per week, stored on ice in the field and transported to the Fruit Research and Extension Center in Biglerville, PA for testing by ELISA. The number of samples of each species varied according to the relative abundance of each species in the field. A total of 10,212 samples were processed in 2003 and none were positive for PPV. The weeds and native tree samples included 66 species from 34 plant families. As in previous years, some
weeds initially gave spurious positive results due to nonspecific binding of the antibody. All suspicious samples were compared with similar samples that were collected from locations about ten miles outside the quarantine zone to check if the result was typical for that species. All questionable samples were tested further until a definitive result was obtained either by additional ELISA tests or if necessary sent to the APHIS lab in Beltsville for confirmation by PCR. The 'PPV surveillance' project was initiated in 2002 and uses herbaceous bait plants as an early detection system for PPV. 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. Several improvements were made to the project in 2003 including the design of custom Styrofoam trays that facilitated transporting plants and provided excellent weed suppression. The surveillance sites were also provided with better
deer and rodent barriers. These improvements saved time and improved bait plant survival. 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 were evidence that the system was theoretically sound. The bait plants were tested for PPV using the Durviz Plum Pox Virus ELISA kit and the results were negative from 5,508 bait plants tested in 2003.
Impacts
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.
Publications
- No publications reported this period
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Progress 01/01/02 to 12/31/02
Outputs
A new plum pox virus (PPV) surveillance project used herbacious alternate hosts as 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. Seventeen 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. The bait plants were tested for PPV using the Durviz Plum Pox Virus ELISA kit and the results were all negative from over one thousand bait plants tested in 2002. A
previous report provides a description of the PPV weed survey project that was initiated in 2000. This project was continued during the 2002 season and tested over ten thousand herbaceous and woody plants. As in previous years some false positive readings for PPV were obtained from certain weeds but these were confirmed to be negative with further testing. In summary, no alternate hosts of PPV were detected.
Impacts
Eradication of PPV will not be accomplished if the virus has managed to become established in native plant species that could serve as reservoirs for future infections. State and federal agencies have established that the criteria for a declaration of successful eradication and for lifting the PPV quarantine in Pennsylvania is three years of negative data but all other survey projects focus on commercial orchards and home owner properties. These projects provide important supplemental information to regulatory agencies to show that PPV has not been found in alternate hosts.
Publications
- No publications reported this period
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