Genetically-Engineered (GE) Corn Pollen: Is It A Source Of Diffuse Pollution?

By John M. Jemison, Jr. and Michael E. Vayda

Introduction

While concern over genetically-engineered (GE) crops continues, usage by U.S. farmers continues to increase. Most of the soybeans and cotton grown in the U.S. are GE, but only about a third of the corn grown in the U.S. is GE. This is partly because the corn weed management appears to be more difficult than that found for Roundup-ready soybeans.  There is also more concern over corn pollen transport. For instance, Maine corn growers who choose to purchase GE seed are provided with information to help them reduce the potential for pollen drift. Maine organic corn growers can have no GE proteins in their feed, and as such GE corn pollen is viewed in Maine as a source of diffuse pollution.  Much like growers are forbidden to spray pesticides when conditions suitable for significant drift, growers have been asked to use setbacks away from other fields to prevent the risk of GE pollen transport. Following a vandalism incident at the University of Maine Roger’s Farm, we received a grant from the Maine Agricultural Center to study corn pollen movement. We established a study from 1999 – 2001 to monitor GE corn pollen movement from a one-acre plot of Roundup-Ready corn into nearby cornfields. The goals of this research were to: 1) determine the optimum timing and rate of glyphosate for Roundup-Ready corn; and 2) determine amount of cross-pollination of GE corn into a conventional corn hybrid. For this paper, we will focus only on the second objective.

Methods

Roundup-ready and conventional corn hybrids were planted at the Rogers Farm in Stillwater, ME between 15 and 17 May 1999, on 20 May 2000, and 17 May 2002. Each hybrid planted was an 83-85 day maturity hybrid. The GE corn (DeKalb DK335 RR) and the conventional hybrid were planted at 78,496 seeds ha^-1. In 1999, the GE study area was 3454 m² located between the two other studies. One recipient field was located 30 m east of the GE study. The other recipient field was located 350 m SW of the GE corn source. Since summer season prevailing winds are predominantly southwesterly, the field 30 m E represented a scenario more favorable for cross-pollination than the weed control study. In 2000, field layout was similar except that the second receiving field was located 105 m S of the GE pollen source. In 2001, we had only one receiving field which was planted to pre-screened open-pollinated corn varieties. This corn was located from 25 – 35 m due E of the GE pollen source. We subdivided each field potentially receiving GM corn pollen into 12 subplots (each subplot was 23.5 m²) to measure cross pollination. Corn was harvested 19 September, 1999, 22 September 2000, and 25 September 2001. Corn (50 ears) was harvested from each 23.5 m² subplot of each study. Corn was dried to < 12% moisture and shelled.  Approximately 200 seeds from each subplot were sown per 0.14 m² flats. The greenhouse screening study was replicated four times each year. The conventional hybrid and DK355 were included with the corn offspring to test purity of initial seed source. Plants were watered daily and fertilized twice with NPK fertilizer. At growth stage V2, glyphosate was applied at 1.12 kg ai ha^-1. After 10 days, plants survival was assessed. Selected glyphosate resistant plants were submitted for polymerase chain reaction tests to confirm the presence of the transgene.

Results 

In 2000, we found significant GE contamination (0.16%) of GE corn in the conventional corn used to monitor drift. So, we will report only on the 1999 and 2001 findings. In 1999, we did not find any cross contamination in the corn planted 350 m southwest of the GE corn. Typical prevailing winds did not favor transport to that site, and we found no survival of corn offspring harvested from that site. We did find some cross-pollination into the conventional corn planted between 30 and 50 m due east of the GE corn (Table 1.)

Table 1.  Cross-pollination Results from 1999.

From these data, it is apparent that the highest amount of cross-pollination occurs is in the conventional corn planted closest to the GE corn, and the amount of cross-pollination drops off with distance from the source.  Again, we found no cross-pollination at the 350m distance from the corn pollen source.  In 2001, we found similar results. In this case, the corn was planted slightly closer to the GE source (25-m E – 35 m E), and there was no distant corn field used to test longer distant pollen travel in 2001 (Table 2).

Table 2.  Cross-pollination Results from 2001.

These data confirm that while cross-pollination does occur, the amount is minimal.  While this work has only been conducted with a small amount of GE source pollen (approximately one acre), it should provide Maine growers with some confidence that if they follow the recommendations provided to them when they purchase the seed, they should be able to limit their risk of cross-pollination. While corn pollen has not been considered to be a source of diffuse pollution, given new USDA organic regulations, perhaps it is time to reconsider this.