Brief Summary of Minutes of Annual Meeting

The 2003 annual meeting of NE1006 was held on Nov. 17-19, 2003 at the U.S. Fish and Wildlife National Conservation and Training Center in Shepherdstown, WV. The meeting was initiated with welcoming remarks by Dr. Dariusz Swietlik, Director of the USDA-ARS Appalachian Fruit Research Station which hosted the meeting. A total of six sessions were held over 1.5 days, each consisting of 3-6 participants giving 15 min oral presentations reviewing work accomplished over the past year (see abstracts). Sessions were organized around general topics including: distribution of PPV in N. Am., PPV strain identification and characterization, State perspectives and results of annual surveys, PPV epidemiology and spread, Developing PPV management strategies and transgenic resistance, and developing innovative systems for information transfer to researchers, extension, and the fruit industry. A short business meeting was chaired by Fred Gildow, Penn State University, in which it was decided to hold next years meeting in Beltsville, MD. Discussion to extend the NE1006 program was delayed until next years meeting.

Meeting Agenda and Abstracts are available in the Minutes attachment.

Over the past two years the NE1006 Project has served to unify several diverse research and survey programs focused on PPV eradication, development of transgenic PPV resistant stone fruit cultivars, and understanding PPV biology required for development of disease management strategies. Major participants in NE1006 included research scientists, extension specialists, and county extension staff associated with the Pennsylvania State University, staff of the Pennsylvania Department of Agriculture associated with the Pennsylvania PPV eradication program, USDA-APHIS-PPQ personnel, USDA-ARS scientists, as well as, researchers and extension personnel associated with several major Universities and State Departments of Agriculture across the U.S. Unquestionably, the major accomplishment of NE1006 was in providing a framework supporting interagency cooperation focused on PPV eradication and on supporting collaborative research among university, state, and federally supported laboratories. This collaboration reduced interagency competition, greatly increased communications, and allowed pooling of limited resources for maximum efficiency. NE1006 can serve as a model for future collaborations required to combat introductions of invasive species or responses to agricultural pathogen introductions associated with biosecurity.

Specific accomplishments over the short life of this project are numerous and diverse. Aphid trapping studies in Adams Co., Mifflin Co., and Center Co. over the past three years by three different labs have identified over 50 aphid species encountered in Pennsylvania stone fruit orchards. Almost all of these aphids are migrant species that do not colonize peach during the growing season. Only 4-5 species occur in high population numbers each year and only one aphid, the spirea aphid, is an efficient PPV vector that occurs midseason in high numbers. Collaborative research among Penn State University and USDA scientists have identified at least 6 indigenous aphid species capable of vectoring Pennsylvania isolates of PPV. Three of these species were very common in Pennsylvania peach orchards and all three were very efficient PPV vectors. This work verified the likely mode of PPV spread within and between Pennsylvania orchards that had been predicted based on epidemiological analysis of patterns of infected trees. This information can be used in developing pest management strategies to reduce vector populations should the eradication effort fail or in the event that PPV is introduced to other areas in the future. Discovery that two species of Pennsylvania aphids could effectively acquire PPV from symptomless peach fruit harvested from PPV-infected trees or from fruit in discarded cull piles, suggested a previously unknown potential mode of PPV spread. Although the level of risk of PPV spread by movement of infected fruit has not been definitively verified in nature, the potential exists for PPV-infected fruit to be shipped long distances and be exposed to aphid vectors. Aphid vectors were demonstrated to feed and survive on harvested stone fruits for up to 1-2 weeks, and aphids were shown to visit and probe on peach fruit hanging on trees or in discarded cull piles. As a result of these finding, greater care was recommended for disposal of discarded fruit derived from commercial packing houses and markets. Because PPV was discovered in Chile several years before its discovery in Pennsylvania, there has been concern for the possibility of importing infected stone fruits as a source of virus. However, random testing of 1400 Chilean stone fruits representing 13 shipments imported into the Port of Philadelphia in 2003 failed to detect any PPV-infected fruit. Therefore, no evidence was obtained to suggest a high risk factor associated with imported fruit. Association of some Pennsylvania PPV infection sites with nearby stone fruit cull piles did suggest that local movement of fruit could be associated with virus spread. Testing of over 16,000 peaches from commercial orchards in four eastern states (Md, N.J., S.C. and Va) in 2003 failed to detect any PPV-infected fruit. To date, infected fruit has only been verified to have occurred in the Pennsylvania quarantined areas.

Research at the USDA Foreign Disease Biocontainment Facility at Ft. Detrick, MD in collaboration with Penn State plant pathologists indicates that Pennsylvania strains of PPV can be inoculated by aphid vectors to many Prunus species of both ornamental landscaping plants and native species typically located in fence rows, woodlots, and forests. This extremely large host range suggests that plenty of possible reservoir host species exist outside of the stone fruit orchard and that it is probably only a matter of time before PPV finds a way to move into one of these hosts and establish a reservoir for virus survival and spread. This fact adds to the urgency for rapid detection and eradication of all known infected plants. In addition to wild bird cherry and choke cherry, PPV was readily inoculated from peach to wild black cherry by two species of aphid. Once in black cherry, PPV retained the ability to be readily inoculated by aphids back to peach. This is significant because black cherry is an economically important lumber species and is extremely common in Pennsylvania woodlands and natural areas throughout the state. Once PPV naturally infects black cherry, eradication would likely become impossible.
In addition, the recent discovery of a PPV-infected dwarf flowering almond shrub in a homeowner landscape suggested movement of PPV by aphids into an ornamental host.
These host range studies and the observation of PPV naturally occurring in an ornamental add justification for continued support of ornamental and wild plant surveys. Over the past year two independent surveillance programs were developed to test for PPV vector spread. One system utilizes young susceptible plum trees as trap plants in previously infected orchard sites. The other system utilizes a series of known herbaceous plant species. These surveillance systems should detect aphids carrying PPV from any unknown PPV reservoir sources should they exist. Fortunately, surveys conducted at the Penn State Fruit Research and Extension Center in Adams Co. PA over the past three years of wild prunus species and other possible PPV host species collected from the quarantine area have all been negative for PPV.

The likelihood of PPV adapting to new host species and developing wild survival reservoirs outside the orchard is being studied. Recent work indicated that PPV surviving in peach was less likely to successfully infect non-prunus herbaceous hosts when compared to infection of prunus species. However, when PPV did infect non-stonefruit species, the virus retained its ability to readily move back into peach. Therefore, if a non-stone fruit species was infected, it could readily serve as a reservoir for continued inoculation of stonefruit orchards. Again, this argues for continued surveying and identification of infected plants and rapid eradication. In the long run, PPV may reinvade the U.S.. This is made more likely by the proximity of the Canadian PPV quarantined zone in Ontario to the fruit growing regions of New York and Michigan. In addition, it is difficult to completely regulate importation of budwood of new cultivars that may be in high demand. Therefore, development of PPV-resistant stone fruit cultivars is highly desired. Because little to no resistance has been identified in peach or plums, recent research at the USDA Appalachian Fruit Research Lab has focused on development of a transgenic plum cultivar. Current field trials in Europe indicate that the cultivar is very resistant to PPV damage. Work is now focused on understanding the molecular resistance mechanism in the hopes that it can be used in other stone fruits. Work at Clemson University is focused on studying the peach genome and genetic background in order to select or enhance host plant genes for induced resistance.


One of the major efforts associated with the NE1006 project included collaborations among University, State, and Federal agencies to carryout PPV surveys nationally and intensively in Pennsylvania. Nationally, in 2003 in addition to Pennsylvania, six states (CA, DE, MD, MI, NJ, and NY) were actively involved in orchard surveys for PPV, These are states at risk because they bordering the Pennsylvania quarantined area ( NJ, DE., MD), have a Prunus major nursery industry (MI), are adjacent to the quarantined area of Ontario, Canada ( MI and NY), or have a huge stone fruit industry of economic importance (CA). A total of 157,000 samples tested negative from these states. In Pennsylvania, the Department of Agriculture PPV lab in Harrisburg tested over 200,000 samples from a 4 county area centered on the quarantine zone of Adams Co. Of these, only 11 were positive (0.005%) and all were closely associated with the current quarantined zone. Of special note was the discovery of a few infected plants in a nursery located 5 miles outside the quarantine zone and 6 mi9les form the nearest known PPV infection site. This required an expansion of the zone into Butler township, Adams Co. Rootstock and budwood sources to the nursery stock all tested negative for PPV. Source of the infection is still unknown. Collaborative work between PDA and PSU-FREC personnel involves an annual wild plant and weed survey designed to detect potential non-Prunus PPV-infected plant reservoirs which could function in PPV survival during the absence of available Prunus species following eradication and before replanting Prunus. Over 10,400 weed plants collected from previous PPV-infected orchard sites were tested in 2003 and none were PPV positive by enzyme immunoassays. None of over 5,000 trap plants set out in old orchard sites became PPV infected. The data reported above indicate that the PPV eradication program enforced by the Pennsylvania Department of Agriculture and USDA-APHIS is being effective in eliminating PPV. However, recent detections of PPV in a few homeowner Prunus trees and in at least one ornamental shrub, and the discovery of a few infected trees in one nursery indicate that eradication is not complete. Because fewer infected trees remain, they are becoming more difficult to detect. In addition, some trees in previously tested healthy orchards may only now begin to show symptoms or develop detectable infections, even though inoculated several years ago, when infected adjacent orchards were nearby prior to eradication. For these reasons, several more years of very intensive testing is required in order to be certain that PPV is truly eradicated.

The resulting publicactions of this work are available in CRIS at http://cris.csrees.usda.gov