GENET archive


2-Plants: GE corn segregation in the U.S.

-------------------------------- GENET-news --------------------------------

TITLE:  Corn Segregation: A Necessary Evil in Today's Biotech Age?
SOURCE: Purdue University, USA, by R. L. Nielsen
DATE:   Apr 23, 2003

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Corn Segregation: A Necessary Evil in Today's Biotech Age?
R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ. West Lafayette, IN 47907-2054
Email address:

The recent approval by the US EPA (2003) of the new rootworm-resistant Bt
corn technology raises again the important issue of corn segregation or
identity-preservation for the purpose of minimizing uncertainty in the
marketplace. This latest plant-incorporated protectant for corn,
developed by Monsanto(TM), is referred to as the YieldGard(R) Rootworm
trait and contains the MON 863 transgenic event that results in the
production of the Bt protein known as Cry3Bb1.

Contrary to the earlier marketed Bt traits, this one targets the pesky
corn rootworm insect rather than the European corn borer. There is no
question that many Indiana corn growers have been waiting impatiently for
this new transgenic trait and are eager to test out hybrids containing
this trait. Supply of hybrid seed for the 2003 season is rather limited,
but will increase markedly in coming years.

As with some other transgenic corn traits (e.g., Herculex(R) Bt, Roundup
Ready(R), most Bt/RR stacked hybrids), Indiana growers need to temper
their enthusiasm with the recognition that the MON 863 trait has not
received global approval in the marketplace, especially with the European
Union (EU). Consequently, some grain buyers may not be willing to
purchase grain of these transgenic hybrids or non-transgenic grain that
contains detectable levels of transgenic contamination. It will be
imperative for growers of the new Bt hybrids to identify buyers who will
accept the grain at harvest time.

The intentions of major grain buyers regarding acceptance of grain from
hybrids not yet approved by the EU is available on the Web (National Corn
Growers Assoc, 2003). In addition, the American Seed Trade Association
(2003) maintains a grain buyer database that helps growers identify
"grain handling facilities that have indicated a willingness to purchase,
receive, and handle genetically enhanced corn products that have full
U.S. registration for food and feed use, but are not yet approved for
import into the European Union."

As with the earlier Bt traits, production of corn hybrids with the MON
863 event will require planting a non-Bt corn hybrid as a refuge to
minimize genetic selection pressure on the pest that may otherwise result
in the development of pest resistance to the Bt protein (Monsanto, 2003).
The refuge design is similar to that for Bt corn borer hybrids, but may
change in the future. According to the US EPA, "A 20% non-Bt corn refuge
is sufficient for a 3 year interim period while additional information is
being gathered. The non-Bt corn refuge should be planted as continuous
blocks adjacent to the MON 863 fields, as perimeter strips, or as non-
transgenic strips planted within the transgenic field. A 20% non-Bt corn
refuge is necessary to produce an adequate number of CRW susceptible to
the Cry3Bb1 protein. Considering the limited movement of CRW larvae,
planting refuges close to transgenic fields in large blocks is preferred
to narrow strips. If a 20% refuge is planted as row strips within a corn
field, then the strips must consist of at least 6 to 12 consecutive rows."

[Table: YieldGard Refuge Designs]
Source: Monsanto

This lengthy introduction finally leads to the important issue of grain
segregation for the express purpose of keeping grain of non-transgenic
hybrids (or transgenics with full market approval) segregated from grain
of transgenics that may require delivery to specific buyers. The US EPA
is requiring that Monsanto make available Cry3Bb1 strip tests to grain
handlers by September 2003. These qualitative tests will be used by some
buyers to detect the presence of the Bt protein in loads of grain that
are purportedly not from MON 863 fields.

Successful segregation of transgenic and non-transgenic grain includes a
number of factors. The most commonly talked about factor is the risk of
pollen drift from transgenic corn fields to non-transgenic corn fields.
Two recently published on-line newsletter articles address this issue
(Gray, 2003; Thomison, 2003), so I won't spend much more time discussing it.

Simply recognize that while it is true that the overwhelming majority of
a corn field's pollen load likely drops very close to the source field,
experience also tells us that small amounts of pollen can travel a
quarter mile or greater and still remain viable (Burris, 2002). Thus,
prudence dictates that growers be aware of what is being grown in
adjacent fields, monitor the calendar dates of pollination among those
fields to determine the risk of cross-pollination, and take appropriate
steps at harvest time if necessary to separately harvest and segregate
grain along field edges within several hundred feet of a possible
contaminant field (Nielsen & Maier, 2001).

Other factors important to successful grain segregation include planter
hygiene, harvesting hygiene, transport hygiene, and grain handling
hygiene (Maier & Nielsen, 2001). The key consideration here is to
identify and eliminate all opportunities for seed or grain commingling
between transgenic and non-transgenic hybrids throughout the entire
production cycle.

Follow the principle of First-In-Field, First-Out-Field (FIF-FOF). This
means that fields of non-transgenic varieties should be planted first to
avoid transgenic seed commingling with non-transgenic seed in the nooks
and crannies of the planter. Similarly, the non-transgenic fields should
be harvested first in the fall before transgenic fields in order to avoid
transgenic grain commingling with non-transgenic grain from the nooks and
crannies of the combine. Obviously, the planter and combine should be
thoroughly cleaned of remnant seed or grain from previous years prior to
their first use this season. Following the FIF-FOF principle will
facilitate proper hygiene of the transport, drying, and grain handling
activities also.


American Seed Trade Assoc. 2003. Grain Handlers Database. Online at [URL verified 4/22/03].

Burris, J. 2002. Adventitious Pollen Intrusion into Hybrid Maize Seed
Production Fields. American Seed Trade Assoc. Online at http:// [URL verified 4/22/03].

Gray, Mike. 2003. Pollen Drift and Refuge-Management Considerations for
Transgenic Hybrids. Illinois Pest & Crop Bulletin, Univ. of Illinois.
Online at [URL
verified 4/22/03].

Maier, Dirk and Bob Nielsen. 2001. GMO Issues Facing Indiana Farmers in
2001. Purdue Univ. Extension publication GQ-46. Online at http:// [URL verified 4/22/03].

Monsanto. 2003. YieldGard(R) Rootworm Insect Resistance Management.
Online at
yieldgardRootworm/irm.pdf [URL verified 4/22/03].

National Corn Growers Assoc. 2003. Processor Marketing Plans Table.
Online at
know_grow_positions_chart.html [URL verified 4/22/03].

Nielsen, Bob and Dirk Maier. 2001. Transgenic Corn Harvest Reminders.
Purdue Univ. Online at
GMO_Harv_Reminder-0913.html [URL verified 4/22/03].

Thomison, Peter. 2003. Managing "Pollen Drift" in Ohio Corn Fields:
Planting Considerations. Crop Observation & Recommendation Network. Ohio
State Univ. Online at
10.html#linkb [URL verified 4/22/03].

US Environmental Protection Agency. 2003. NEW CORN PEST CONTROL APPROVED
Conventional Insecticides For Control Of Corn Rootworm. US EPA National
Press Release. Online at
83e5ad62660c85256cd800729c3c?OpenDocument [URL verified 4/22/03].