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:
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.
“Bobwhite GM lines [mother plants] containing the Pm3b transgene
were six times more likely than non-GM control lines to produce outcrossed
“There was additional variation in outcrossing rate among the four
GM-lines, presumably due to the different transgene insertion events.”
GM lines Pm3b#2 and #4 had “strongly increased levels of
ergot infection” and had “reduced male fertility.”
“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.”
1. See, for example, two of our reports — one on
contamination in general and one on contamination of canola seedlots.
Rieben, Silvan., Olena Kalinina, Bernhard Schmid and Simon L. Zeller
(2011). “Gene Flow in Genetically Modified Wheat,” Plos ONE vol. 6,
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