Genetically modified plum trees with resistance to plum pox, a virus that can devastate stone fruit, have moved a step closer to reality, according to the Agricultural Research Service.

The Animal and Plant Health Inspection Service, which has regulatory authority over genetically engineered organisms, recently "deregulated" HoneySweet, as the plum pox-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.

ARS is 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 plum pox virus 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 plum pox virus through a process called gene silencing.

While HoneySweet itself produces high-quality fruit of commercial standard, it also may be used as breeding stock to introduce plum pox virus 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 Food and Drug Administration and the Environmental Protection Agency.

Plum pox, also known as sharka, was first identified in the United States in Pennsylvania in 1999 and has since been found in New York and Michigan.