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Posted: May 2014

GM wheat outcrosses more often than unmodified wheat of the same varieties

While wheat plants usually self-fertilize, they do occasionally cross-pollinate with other wheat plants (“outcrossing”). There is concern that if GM wheat were to be commercialized and the seed supply of conventional or organic wheat were to be contaminated with even small amounts of GM wheat, that occasional outcrossing could lead to increasing numbers of GM/non-GM hybrids in conventional and organic wheat fields.

Researchers in Europe (Rieben et al. 2011) compared the outcrossing rate of GM wheat (different lines of the varieties Bobwhite and Frisal, both resistant to fungi) and non-GM wheat of the same varieties. They planted small amounts of GM wheat in plots with non-GM wheat. As expected, the overall outcrossing rate was low (3.4%). But they found:
  1. “Bobwhite GM lines [mother plants] containing the Pm3b transgene were six times more likely than non-GM control lines to produce outcrossed offspring.”
  2. “There was additional variation in outcrossing rate among the four GM-lines, presumably due to the different transgene insertion events.”
  3. GM lines Pm3b#2 and #4 had “strongly increased levels of ergot infection” and had “reduced male fertility.”
  4. “Hybrids with two or even three transgenes can occur if different GM plants are planted in close proximity. Such plants could further complicate environmental risk assessment.”
The unexpected higher rate of outcrossing by the GM lines increases concern about the likelihood of GM wheat hybridizing with non-GM wheat should the seed supply be contaminated with even small amounts of GM seed. “Each GM plant is likely to outcross with several neighbors which will result in plants heterozygous for the transgene. The proportion of GM plants within a population is therefore likely to increase.” Since some mixing of GM and non-GM seed can be expected1, organic and conventional farmers are faced with the likelihood of hybridization with GM crops, even in the case of the predominantly self-fertilizing wheat. EU regulations stipulate that an organic crop may not have greater than 0.9% GM contamination. As of 2014, GM wheat has not yet been approved for commercialization in the U.S. or in the EU.


1. See, for example, two of our reports — one on seed contamination in general and one on contamination of canola seedlots.

Source: Rieben, Silvan., Olena Kalinina, Bernhard Schmid and Simon L. Zeller (2011). “Gene Flow in Genetically Modified Wheat,” Plos ONE vol. 6, e29730.

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