European Plant Protection Organization
While lending a hand with some pruning work in a Scotian Gold Cooperative apple grower’s orchard last summer, fieldman Larry Lutz noticed some strange growth on several trees, so he notified the Canadian Food Inspection Agency.
Testing showed it was apple proliferation phytoplasma (APP) in the orchard near Kentville, Nova Scotia.
The affected orchard of five-year-old Pacific Gala on B. 118 rootstock was placed under quarantine, and the source of the trees identified. They came from a nursery in Washington State, budded to roots from a nursery in Oregon.
The Canadians notified the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS), which began sampling and testing in Washington and Oregon. APHIS said this is the first confirmed finding of APP in North America. It is a quarantine pest in both the U.S. and Canada. It is present throughout Eastern Europe.
In response to questions from Good Fruit Grower, APHIS public affairs representative Tanya Espinosa, said: “The source of the infestation is unknown. However the infected plants were imported from Washington in 2008-09. The Washington nursery used rootstock from an Oregon nursery. No symptoms of APP have been observed in the source nurseries or reported in the U.S. at large. Sampling and testing are occurring in Oregon and Washington.”
APHIS has provided trace-forward information to the Canadian agency.
In Ottawa, the Canadian Food Inspection Agency’s media relations representative Elena Koutsavakis, said the Canadian grower with the infected trees will not be much affected.
“The affected orchard has been placed under quarantine,” she said. “This means that the grower cannot propagate from or move the trees in the affected orchard. Regular orchard management can still be applied to the orchard as APP is not spread through pruning, seed, or fruit.”
The agency is gathering information to determine whether further regulatory response is needed. Information is being shared with industry and national stakeholder groups, she said.,
Lutz said the disease is difficult to detect in dormant wood, as the phytoplasma organism retreats to the roots in the winter, but testing will be done later.
It is not considered an emergency situation. “It doesn’t spread easily,” Lutz said, “mostly by grafting infected wood.”
APP, or Candidatus phytoplasma mali, is present throughout Europe, where it is considered to be one of the most critical diseases of apple trees, APHIS said in a statement. “APP is spread through propagation practices with infected material including budding and grafting. Long-distance dispersal of APP occurs through the trade of infected rootstock, scion wood, or budwood. It is not transmitted through seed or pollen or fruit or pruning.”
Reportedly, it is spread in Europe by some insects, like leafhoppers, but in scientific tests, transmission by other than infected wood has been hit and miss. It is not known whether any North American insects could vector the disease.
A data sheet from the European Plant Protection Organization says that symptoms of APP include shoots around axillary buds, which create a broom-like appearance at the end of affected branches and gives the malady its name. It is called witches’ broom in some parts of Europe. Late growth of terminal buds in the fall is usually the first noticeable symptom. It also causes leaf rosetting, enlarged leaf stipules, reduced growth, and smaller, poorly flavored fruit that is both less sweet and less acidic.
Diseased trees may die, or they may recover and, if adequately fertilized, produce normal fruit, according to the data sheet.