Methods for Detecting GMOs in Grain Crops
September 20, 2001 8(25):161-164
Joe Lauer, Corn Agronomist
The following is an edited excerpt from a review on detecting transgenic genes in
crop plants written by Dr. Peter Thomison at Ohio State University.
As market restrictions for various transgenic (genetically modified organism or
GMO) crops (e.g. Bt-corn, Roundup Ready soybeans and corn) continue, there is increasing
interest among growers in determining the presence of GMOs in crops. Growers producing
non-GMO grains for specialty markets need to verify that there is no GMO contamination
or that contamination levels meet tolerance levels established by an end user. The
default standard for certification as GMO free has been taken to be zero in many
cases, although experience shows that meeting such a standard will be difficult.
There have been proposals for setting maximum allowable levels in the range of 1
to 3%, and it's likely that some tolerance level above zero will be accepted
in the future. Japan recently established new legislation that sets a zero tolerance
for seed and food imports containing unapproved biotech material, e.g. StarLink
corn (containing the Cry9C Bt transgene). The Japanese legislation will allow food
products containing less than 5 % of approved biotech crops like corn and soybeans
to be labeled as non-GMOs. The European Union (EU) has recently proposed rules on
the labeling and traceabililty of foods containing GMOs. According to these new
rules, accidental traces of GMOs that have been cleared by the EU's scientific
advisers, even if they have not received final official approval, will be allowed
in food and feed up to a maximum of 1% without being subject to labeling requirements.
Other countries importing U.S. grains are considering tolerances similar to those
of Japan and the EU.
There are also other circumstances when GMO testing may be useful in crop production,
such as when troubleshooting crop disorders during the growing season. If an allegedly
herbicide resistant corn or soybean field exhibits extensive injury following herbicide
application, the grower may want to confirm that plants in the field are actually
herbicide resistant. Similarly a grower, if uncertain, may need to determine what
fields, or what parts of fields, he planted to GMO crops.
There are several commonly used GMO testing protocols, including biological tests,
as well as ELISA and PCR tests, for herbicide and insect tolerance. Growers and
end users should consider the advantages and disadvantages of the various testing
methods before harvest. Exporters should probably resign themselves to the most
rigorous testing protocol to anticipate the additional scrutiny their products will
receive overseas. Some major end-users, i.e. large food processors, are currently
using a combination of tests for identity-preserved (IP) grains.
Herbicide bioassays are used to detect GMO herbicide resistant traits in Roundup
Ready and Liberty Link soybeans and corn. The tests involve placing seeds in a germination
media moistened with a diluted solution containing the herbicide or spraying the
herbicide on seedlings. Seeds that test positive for the presence of the herbicide
tolerant GMO trait will germinate and develop normally, whereas those that die or
do not develop normally will be GMO-free. This procedure is widely used by seed
and grain companies exporting soybeans. Advantages of the bioassay method: it's
relatively inexpensive ($20 -$30), user friendly, and produces straightforward results.
Disadvantages of the test: it takes up to a week to complete, its use is limited
to the Roundup Ready and Liberty Link herbicide resistant GMO crops, and the seeds
need to germinate for the test to work. Herbicide bioassays can also be used to
detect herbicide resistant traits in non-GMO corns such as ClearfieldÂ® hybrids which
are tolerant to imidazolinone herbicides (Pursuit, Scepter, Lightning).
ELISA (enzyme-linked immunosorbent assay) tests for the presence of the specific
protein that the genetically modified DNA produces in the plant. ELISA procedures
use antibodies that react with specific proteins produced by the GMO. There are
different versions of the ELISA method used for GMO detection. One version uses
lateral flow strips and delivers results in 2 to 5 minutes. This "strip test"
technology is similar to that used in-home pregnancy tests. Strip tests are commonly
used at grain elevators where a rapid assessment to determine the presence or absence
of GMOs is needed. Some companies marketing this ELISA technology for seed testing
refer to these tests as the "dipstick" procedure. Another version of the
ELISA test, the "plate test", provides some indication of the quantity
(percentage) of the tested sample that is the GMO in question. Intensity of color
indicates the amount of the protein present. The plate test can take 2 to 4 hours
and is more laborious, and costly than the strip test. Advantages of the ELISA strip
tests are speed, relative ease of use, and low cost. The major disadvantage of the
strip test is that it cannot quantify how much GMO is present. ELISA tests have
limited application for testing GMOs in processed foods because heat processes denature
the proteins, thereby making detection of proteins difficult.
The PCR (polymerase chain reaction) method is more sensitive than the ELISA method
and tests for the presence of the specific DNA sequence of the gene itself. The
major advantage of PCR tests is sensitivity, i.e. detection of GMOs at very low
levels. PCR is the only one of these methods that can effectively detect GMOs in
processed foods. Major disadvantages of the PCR protocol include length of time
needed (2-3 days), and cost ($75-$300 per sample). PCR tests also require more sophisticated
equipment and greater expertise. While more sensitive to GMOs, PCRs in some cases
tend to show false positives. PCR procedures were originally developed as research
tools for analyzing genes and assisting in the movement of genes among organisms.
Given the expense, time, and expertise required, PCR testing has limited potential
in the field or at grain elevators.
As the number of GMO traits increases (e.g. GMO corns with resistance to Roundup,
European corn borer, and western corn rootworm), it will become more costly to monitor
the presence of GMOs in crops, since each different gene requires a separate test.
However, if the demand for non-GMO crops increases, it's possible that tests
for different genes may be combined on the same ELISA test strip.
Although some of these GMO testing procedures such as the ELISA strip tests can
be used in the field and elevators, the other procedures for detecting GMOs require
more sophisticated training and equipment to be used effectively. The following
is list of some of the laboratories that offer GMO testing of grain crops for a
fee. The websites for these labs provide an overview of the specific GMO testing
procedures they conduct. The following are some commercial laboratories testing
for GMOs in crops (as of 7-10-01):
Central Hanse Analytical Lab LLC
101 Wordland Hwy
Belk Chasse, LA 70037
504-393-5290; fax 504-393-5270
Biogenetic Services Inc.
801 32nd Ave
Brookings, SD 57006
605-697-8500; fax 605-697-8507
California Seed & Plant Lab, Inc.
7877 Pleasant Grove Rd
Elverta, CA 95626
916-655-1581; fax 916-655-1582
1760 Observatory Dr
Fairfield, IA 52556-9030
888-229-2011; fax 641-472-9198
Mid-West Seed Services
236 32nd Ave
Brookings, SD 57006
605-692-7611; fax 605-692-7617
Ohio Seed Improvement Association
6150 Avery Rd, Box 477
Dublin, OH 43017-0477
614-889-1136; fax 614-889-8979
30380 Country Road 6
Elkhart, IN 46514
219-264-2014; fax 219-264-2153
507 Highland Dr
River Falls, WI 54022
715-426-0246; fax 715-426-0251
Indiana Crop Improvement
770 Stockwell Rd
Lafayette, IN 47909
765-523-2535; fax 765-523-2536
Illinois Crop Improvement
3105 Research Rd, PO Box 9013
Champaign, IL 61826-9013
217-359-4053; fax 217-359-4075
OTHER REFERENCES RELATING TO GMO TESTING
The Non-GMO Source. 2001. An Overview of GMO Testing Methods. 1:4 Biotechnology
Issues on the Web.2001 Purdue University. www.agry.purdue.edu/ext/corn/cafe/biotech.html