by: George Place and Major Goodman

Genetic contamination of organic corn with genetically modified (GM) genes is a growing concern for organic producers. While corn pollen does not travel far in comparison to many other grass species, if temperature, humidity, and wind are favorable, corn pollen can travel thousands of feet. Research has indicated that cross-pollination between corn fields could be limited to 1% or less on a whole field basis by a separation distance of 660 ft., and limited to 0.5% or less on a whole field basis by a separation distance of 984 ft. However, cross-pollination could not be limited to 0.1% consistently even with isolation distances of 1640 ft.
Organic certifying agencies and organic grain buyers will need to know how organic corn farmers avoided genetic contamination from neighboring GM corn crops. Some buyers (and all who ship product to Europe) will utilize an ALIZA type test that can detect a GM protein in the corn and will reject loads that are above a certain percentage. Contamination tolerance levels are 0.9% or less to still qualify as organic in the European Union. The USA does not have a set threshold of contamination tolerance for organic certification but many buyers are establishing their own product threshold.
To reduce genetic contamination farmers must plan ahead to spatially or temporally distance organic corn from conventionally-grown corn. Organic corn should be planted at least 660 feet from any neighboring GM corn (or conventionally-grown corn), if possible. This may mean planning a rotation around what your neighbors are doing. If distance separation is not possible, another strategy is to plant later or earlier than your neighbors so that your corn is pollinating at a different time. A typical corn plant will shed pollen for 5 to 6 days, a whole field will usually complete pollen shed in 10 to 14 days. If a GM corn producing neighbor is planting a 110 day corn hybrid the organic corn producer could plant a later maturity hybrid (say 118 day corn) 10 days after his neighbor has planted. This would create a maturity separation of 18 days, leaving plenty of time for the neighbor’s GM corn to complete pollination. However, the organic producer must be careful not to confuse this temporal separation. If the neighbor is planting a later maturity variety (118 day), then the organic producer wanting temporal separation would also need to chose a later maturity variety (118 day or later) and plant at least two weeks later (pollination times could match if the organic producer chose an earlier maturing hybrid and planted later). Temporal separation strategies also must take into account that rarely could the organic corn producer plant earlier than the GM corn since organic corn seed is untreated and susceptible to early season diseases. To significantly reduce any genetic contamination that may have occurred despite these measures, many farmers harvest the outside rows of their organic corn separately and sell it on the conventional market. The number of buffer rows needed depends on how susceptible the field was to cross pollination contamination.
Dr. Major Goodman, NCSU corn breeder, is currently working on the development of a corn hybrid that will alleviate fears of cross pollination contamination by neighboring GM corn. These organic corn hybrids will utilize what is known as the GA1-S isolating mechanism. This is a naturally occurring gene in corn that stops pollen originating from a plant that does not have the GA1-s gene from being able to pollinate a plant that does have the GA1-s gene. This crossing barrier is utilized extensively in commercial popcorn hybrids since popcorn hybrids are grown in the mid-west, as is dent, or field corn. If a popcorn ear is pollinated by dent corn pollen then the resulting popcorn kernel does not behave as a true popcorn — which would irritates a whole lot of movie goers. Thus popcorn hybrids that have the GA1-s gene do not accept pollen from the surrounding GM field corn hybrids that do not have this GA1-s gene. Dr. Goodman is putting this system into several of his corn inbreds to produce corn hybrids for organic production that cannot be pollinated by adjacent fields of GM hybrids. Of course, they could be pollinated by GM popcorn hybrids, but the good news is that popcorns are not grown in the southeast.