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United States Department of Agriculture

Agricultural Research Service

Plum Pox FAQ - More information for the plum orchard industry

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More information for the plum orchard industry—

I have an organic plum orchard. How do I keep pollen from HoneySweet from reaching my trees?
To find out how far HoneySweet plum pollen will travel to other plum trees, almost 3,000 seeds were evaluated over six years at distances from 230 to more than 3,500 feet from the HoneySweet planting. Over the six years of the test, only two seeds were found to have received HoneySweet pollen. These were at a distance of about 1,700 feet from the HoneySweet trees. So to ensure pollen does not mix, non-GE plum trees should be grown more than 1,700 feet (about 1/3 mile) from HoneySweet trees.

The inserted genes in ‘HoneySweet’ would be found in 50 percent of the pollen grains of ‘HoneySweet’. If a pollen grain carrying the inserted genes would fertilize another plum tree the pollen grain would fertilize the ovule which forms the seed. It is important to understand that the flesh of plum fruit is exclusively derived from the maternal tree (non-GE tree in this case) and the cells of the fruit flesh and skin are genetically identical to the cells of the maternal (non-GE) tree. Therefore, even in the rare instance of cross pollination between a GE ‘HoneySweet’ and a receptive organically or conventionally non-GE grown tree, the resulting edible portion of the plum fruit (i.e., flesh and skin) would contain no GE DNA in its cells. Although the plum stone, or pit, resulting from the cross pollination described above, could contain GE DNA, plum trees are not normally propagated from seeds. Instead, they are clonally propagated from another tree of the desired variety usually by grafting. A twig from such a tree is grafted onto an existing plum rootstock. The plum seed is not normally used for producing new plum trees nor are plum seeds used as food. The seed is bitter due to the presence amygdalin so people naturally refrain from eating it. Moreover, amygdalin, upon digestion, produces cyanide.

Clearly, cross pollination cannot change the genetic background of the tree receiving pollen from a ‘HoneySweet’ tree. The biology of plum fruit development and the method used for plum propagation ensure that in the unlikely event of a cross pollination from pollen of ‘HoneySweet’ and an organically or conventionally non-GE produced tree, the edible portion of the fruit and the tree itself will not be genetically altered.

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Last Modified: 7/23/2007