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Tennessee fights rust with DNA analysis

If Asian soybean rust enters west Tennessee this season, soybean farmers should know about it even before the disease’s lesions show up in sentinel plots, thanks to a project sponsored by the Tennessee Soybean Promotion Board.

Sentinel plots consist of early-maturing soybeans, planted earlier than usual so that the plot achieves canopy closure quickly. Under the right environmental conditions, rust should first appear in the sentinel plots, giving growers some lead time (one to three weeks) for treating their soybean fields for rust, if necessary. The University of Tennessee has planted 24 sentinel plots in the state.

But west Tennessee is adding another layer of diagnostics to the sentinel plots, using DNA analysis to detect the disease very early in its development, according to University of Tennessee plant pathologist Melvin Newman.

“The Tennessee Soybean Promotion Board has provided funds for weekly polymerase chain reaction (PCR) testing of samples from all 24 locations in west Tennessee, beginning in mid-May. The test can be run on anything that contains DNA. It will be used to determine if rust is present long before symptoms, including lesions, show up on the plant. We will be able to detect the disease before you can see it.”

The PCR test can give the producer even more time — an additional week, perhaps, of advance notice of the disease’s movement.

Soybean plants from Tennessee’s 24 sentinel plots will be sampled at random each week, and leaves packaged and delivered overnight to a Knoxville laboratory set up by Kurt Lamour, University of Tennessee plant pathologist.

Lamour will scrape any suspicious-looking spots on leaves and run the samples through DNA analysis. “If there is any rust in that sample, the test can pick it up and in 24 hours, he’ll have an answer on whether the plot has rust,” Newman said. “It’s very specific and very accurate. As far as I know, we’re the only state that is doing this on a weekly basis. Once rust is found in a particular sample, further samples will not be taken.

“In addition, over 200 Extension agents and first detectors have been trained to use hand lens and microscopes to detect the disease. The agents will also photograph and send images of possible occurrences of rust via the Internet to the state’s Distance Digital Diagnostics program.”

The images can be observed by diagnosticians at Tennessee’s primary diagnostic laboratory at Ellington Center in Nashville.

“A lot of our county agents have microscopes in their offices and received a lot of training this winter. They’re going to help us quite a bit in the field, not only on the first diagnosis, but determining the severity of the disease as the season progresses.”

Newman added that UT will also monitor a handful of other plots at the West Tennessee Experiment Station in Jackson, Tenn., to determine the susceptibility of clovers and legumes to Asian soybean rust.


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