Farmers who grow non-genetically modified organism (GMO) crops for specialty markets can utilize a variety of tests to ensure that their crops are GMO-free.
A number of tests measure levels of herbicide and insect tolerance in such crops as corn and soybeans.
"These tests are commonly used by grain elevators, crop consultants and others when they check grain before it's sent off to market," said Peter Thomison, Ohio State University agronomist.
The tests can determine what percentage of a crop, if any, contains GMOs, allowing producers to compete in national and international grain markets where non-GMO certification standards are strict.
Currently, the standard for GMO certification is set at zero tolerance, although several proposals have been developed to set the maximum allowable levels between 1 percent and 3 percent.
Japan recently introduced legislation that sets a zero tolerance for seed and food imports containing unapproved biotech material. StarLink corn is one such example. The Japanese legislation also requires food products containing less than 5 percent approved GMOs be labeled non-GMO products.
The European Union (EU) also has proposed rules on the labeling of foods containing GMOs. EU rules would allow food and feed to contain up to 1 percent GMO material without being labeled a GMO product.
"I would imagine a grower would be in quite a bind if the contamination level of his crop exceeded that 1 percent or the tolerance level that is set by the end user. He'd have to sell his corn or soybeans at the conventional market," Thomison said. "This is something that organic producers are concerned about. They want to make sure their end users are willing to take their products, and these tests will help them achieve that."
The most common types of GMO tests used include herbicide bioassays, enzyme-linked immunosorbent assay -- or ELISA -- and the polymerase chain reaction (PCR) method.
Herbicide bioassays are used to detect GMO herbicide-resistant traits in Roundup Ready and Liberty Link soybeans. The test involves placing seeds in a germination medium containing diluted solution with the herbicide, or directly spraying the seeds with the herbicide. Seeds that develop normally test positive for the GMO herbicide trait, while those that die or do not develop normally are considered GMO-free.
The assay is inexpensive -- $20-$30 -- but test results can take up to a week.
ELISA tests detect the presence of a specific protein that the GMO DNA produces in a plant. Several versions of ELISA exist, including the "strip test" or "dipstick" procedure that uses lateral flow strips and delivers results in 2-5 minutes, and the "plate test" that uses color intensity to determine what percentage of the grain is GMO material.
The PCR method is more accurate than ELISA, in that it measures exactly where the GMO is present on the DNA gene sequence. The PCR method is highly sensitive but can take up to three days to complete. PCRs cost between $75 and $300 per sample.
"A typical procedure for a food-grade corn or soybean producer, for example, might be for him to test samples or ask a certifying association to come out and monitor his field throughout the season," Thomison said.
"The association would then certify his field as non-GMO and finalize the procedure by taking samples of grain from the field and checking it in their lab. The grower would then present that certification to the end user, who would probably turn around and retest the product again."
The tests are designed to identify traits of different GMO "events," such as Bt corn or Roundup Ready or Liberty Link herbicide-resistant soybeans, Thomison said. End users would subject a farmer's grain to a battery of tests based on the types of crops grown in Ohio and how prevalent the GMO events would be, he said.
Presently, six GMO events exist. A new GMO event, rootworm Bt, is expected to be released to the market next year.
"While there is a sizable number of farmers who want GMO crops, there are also a number who don't want them either," Thomison said. "Some farmers don't want GMO crops because they have reservations about possible risk to human health and adverse effects to the environment. Others are somewhat indifferent to the GMO issue and are trying to take advantage of the market that is there.
"The industry hopes that the furor of GMO products will die down when the public sees there are no negative issues resulting from the use of GMO products."
Ohio State University's Crop Observation and Recommendation Network (C.O.R.N.) newsletter contains a list of labs that test crops for GMOs. The newsletter is available online at http://corn.osu.edu/archive/2001/sep/01-31.html#linkc  .