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Assessing the Spread of Engineered TMV

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Science  29 Oct 1999:
Vol. 286, Issue 5441, pp. 901
DOI: 10.1126/science.286.5441.901f

In Trisha Gura's News Focus article “New ways to glean medicines from plants” (27 Aug., p. 1347), tobacco mosaic virus (TMV) engineered by Biosource Technologies Inc. to carry human genes is said to be unlikely to spread in the environment because “they [Biosource] found no detectable virus outside of plants after 2 or 3 days….” Presumably the assays were done 2 or 3 days after the plants were sprayed with TMV to infect them. One cannot make any conclusions about the likelihood of engineered TMV spreading from the plants on the basis of such assays. A more meaningful test would be to look for the spread of TMV to susceptible plants (crop or weed hosts) growing near the experimental plants throughout the time these plants are grown.

TMV is not spread from plant to plant by a specific biological vector but, rather, by mechanical means that may involve such diverse agents as the claws of aphid's feet, the hoses used to water plants in the greenhouse, and the hands or clothing of workers who touch healthy plants after handling or brushing against infected plants. Furthermore, the virus can be transmitted mechanically from the dry residue of roots, shoots, or leaves of infected plants after they die and dry out. It also contaminates greenhouse structures, where it survives to infect the next susceptible crop.

To assess the risk of release, one might better ask how far experimental plants are grown from tobacco fields in Kentucky or tomato fields in California and the precautions taken to prevent “traffic” between said fields.

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