Plum pox is a serious viral disease of stone fruit species that was detected, in 1999 for the first time in North America, in a Pennsylvania orchard. The plum pox virus (PPV) can be transported long distances in infected plant material and is transmitted from infected trees by insects or by grafting or budding. PPV does not kill trees, but it reduces the yield and marketability of fruit. In addition, PPV does not affect human or animal health.
Subsequent to its discovery in the United States, an infestation of plum pox virus was detected in Ontario and Nova Scotia, Canada. It appears that this infestation pre-dates the detection of plum pox. At this time there is no evidence that the two infestations are related. The PPV strain detected in the United States and Canada is the D strain or PPV-D. PPV-D was originally described from Europe, is not the most virulent of plum pox strains, and does not appear to infect cherry species.
In March of 2000, the United States Secretary of Agriculture declared an extraordinary emergency in order to prevent the spread of the virus from Pennsylvania to the rest of the United States and to other countries. The emergency declaration allowed the United States Department of Agriculture to provide the funding necessary for eradication and to pay compensation to affected growers. Through surveying and removal of infected and exposed trees, PPV was eradicated from Pennsylvania. The Federal plum pox quarantine for Pennsylvania was rescinded on October 29, 2009, following 3 years of negative survey results.
In 2006, PPV was detected in Michigan. A single plum tree located at a Michigan State University facility located near Benton Harbor, Michigan was determined to be infected with PPV. The infected tree was destroyed and, through trace-forward and trace-back investigations, no additional trees in Michigan were found to be infected with PPV. Plum pox is considered eradicated in Michigan.
PPV was detected in New York State in 2006 and is currently under eradication. Survey and eradication efforts, in cooperation with the New York Department of Agriculture, are currently ongoing. State and Federal quarantine regulations have been imposed to prevent the spread of PPV from impacted areas in New York State.
Plum pox occurs on Prunus species including peaches, nectarines, apricots, plums, almonds, cherries, and some ornamental Prunus cultivars.
Plum pox was first reported in Bulgaria in 1915 and is known to occur in Europe, the Middle East, North Africa, India, Chile, and Canada.
In the United States, PPV is known to occur in Niagara, Orleans, and Wayne counties in New York.
Symptoms and Identification
Trees infected with PPV show an uneven distribution of the pathogen within the tree. Symptoms of infection appear on leaves, flowers, and fruit but may vary considerably depending on the tree species or cultivar. Fruits can become distorted in shape and show characteristic ring or spot blemishing. Flowers may have streaking on the petals or pigmented ring patterns, commonly referred to as color break. Leaves can have rings or show light green or yellow veining, have a distorted shape and prematurely drop. Seeds may appear deformed, and discolored.
Sometimes infected trees display no symptoms on the leaves or fruit at all. To confirm the presence of virus in trees that appear to be symptom-free, molecular diagnostic tests must be performed on sample plant tissues.
Biology and Disease Spread
The virus that incites plum pox is spread from plant to plant by insects called aphids. Several aphid species can serve as vectors for the spread of PPV, varying in efficiency by the species of aphid, strain of virus, and host species affected. The aphids suck sap from infected plants and then carry the PPV to other plants. The virus stays viable in the aphid's mouthparts for approximately one hour and most aphids can generally transmit infection up to 120 meters from the initial source plant.
PPV can be transported long distances in live nursery stock, and by budding and grafting with infected plant material.
Plum pox, also known by as sharka (the Slavic name for plum pox), is the most devastating viral disease worldwide of stone fruit. Infection of susceptible host species weakens the trees and eventually results in severely reduced fruit production. The fruit that is produced is often misshapen and blemished. The presence of PPV can enhance the damaging effects and increase the economic losses caused by other endemic viruses infecting various species of the genus Prunus. Plum pox poses no danger to consumers; however, it can ruin the marketability of stone fruit by causing acidity and deformities. Plum pox can decrease the yield of infected trees. The severity of the disease depends on the strain of the virus present and the susceptibility of the Prunus cultivars under production.
Control and prevention measures for PPV include field surveys, use of certified nursery stock, use of resistant varieties (when available), control of aphid vectors, elimination of infected trees, and enforcement of domestic and international quarantine regulations. In the United States, trees, seedlings, root stock, budwood, branches, twigs, and leaves of host Prunus species are regulated. Seeds and fruit are not pathways to spread PPV and are therefore not regulated.