By Kim Kaplan
Plum trees with resistance to plum pox (PPV), a virus that can
devastate stone fruit, have moved a step closer to reality, according to the
Agricultural Research Service (ARS), which is leading the project.
The U.S. Department of Agriculture's Animal and Plant Health
Inspection Service, which has regulatory authority over genetically
engineered organisms, recently "deregulated" HoneySweet, as the
PPV-resistant plum tree is named. This means APHIS had determined that the
tree is not a plant pest and that it will have no significant impact on
other plants.

Deregulated products have a history of safe use in U.S. agriculture.
APHIS has overseen the deregulation of more than 70 genetically engineered
plants, including corn, cotton, rapeseed (canola), soybean, flax, sugar beet
and squash. In September 1996, papaya became the first genetically
engineered tree to be deregulated.

ARS is now taking the next step in HoneySweet's development, which is
for cooperators such as universities to plant small quantities of the trees
to study how they grow under a variety of conditions, a process commonly
undertaken for new varieties.

A standard genetic engineering technique was used to introduce a gene
for the PPV coat protein into cells extracted from plum seeds. Cells that
incorporated the new gene into the plum DNA were then regenerated and grown
into complete plum trees. These trees have the new gene in their DNA and are
resistant to PPV through a process called gene silencing.

While HoneySweet itself produces high-quality fruit of commercial
standard, it may also be used as breeding stock to introduce PPV resistance
into other plum breeding lines for future variety development. Fruit from
HoneySweet or its progeny will not be eaten or sold without further
regulatory approval by the U.S. Food and Drug Administration and the U.S.
Environmental Protection Agency.

PPV was first identified in the United States in Pennsylvania in 1999
and has since been found in New York and Michigan. To ensure that PPV was
eradicated during the 1999 outbreak, over 1,600 acres of commercial orchards
and homeowner trees had to be destroyed at a cost of more than $40 million.

But since developing a PPV-resistant plum tree is not a simple or
quick process, ARS has not waited until plum pox has a major presence in the
United States to do the research. Rather, ARS has taken the proactive step
of developing a PPV-resistant tree and doing the testing required to allow
genetically engineered trees to become available before plum pox
precipitates a crisis in this country.

More information about the HoneySweet plum tree can be found at
[www.ars.usda.gov]