Abstract
Understanding gene flow in genetically modified (GM) crops is critical to answering questions regarding risk-assessment and the coexistence of GM and non-GM crops. In two field experiments, we tested whether rates of cross-pollination differed between GM and non-GM lines of the predominantly self-pollinating wheat Triticum aestivum. In the first experiment, outcrossing was studied within the field by planting “phytometers” of one line into stands of another line. In the second experiment, outcrossing was studied over distances of 0.5–2.5 m from a central patch of pollen donors to adjacent patches of pollen recipients. Cross-pollination and outcrossing was detected when offspring of a pollen recipient without a particular transgene contained this transgene in heterozygous condition. The GM lines had been produced from the varieties Bobwhite or Frisal and contained Pm3b or chitinase/glucanase transgenes, respectively, in homozygous condition. These transgenes increase plant resistance against pathogenic fungi. Although the overall outcrossing rate in the first experiment was only 3.4%, Bobwhite GM lines containing the Pm3b transgene were six times more likely than non-GM control lines to produce outcrossed offspring. There was additional variation in outcrossing rate among the four GM-lines, presumably due to the different transgene insertion events. Among the pollen donors, the Frisal GM line expressing a chitinase transgene caused more outcrossing than the GM line expressing both a chitinase and a glucanase transgene. In the second experiment, outcrossing after cross-pollination declined from 0.7–0.03% over the test distances of 0.5–2.5 m. Our results suggest that pollen-mediated gene flow between GM and non-GM wheat might only be a concern if it occurs within fields, e.g. due to seed contamination. Methodologically our study demonstrates that outcrossing rates between transgenic and other lines within crops can be assessed using a phytometer approach and that gene-flow distances can be efficiently estimated with population-level PCR analyses.
Highlights
The frequent use of genetically modified (GM) plants in agriculture demands in-depth ecological risk assessment [1]–[6]
There was significant variation among the four GM lines which could be explained by a contrast between line Pm3b#2, which had fewer hybrids, and the other Pm3b lines (P = 0.018)
Our results show that GM lines of wheat can differ in their outcrossing behavior from non-GM control lines
Summary
The frequent use of genetically modified (GM) plants in agriculture demands in-depth ecological risk assessment [1]–[6]. Gene flow can increase the ability of a population to respond to a changing environment due to increased genetic diversity [13]. Gene flow occurs by migrating individuals (seed dispersal) and by migrating gametes, i.e. pollen dispersal. Gene flow via pollen dispersal can occur within and between populations and occasionally even between species [14], [15]. Understanding this process is critical to ensuring the coexistence without gene exchange of GM and non-GM crops [16], [17]. Data about pollen-mediated gene flow are essential to establish appropriate isolation distances between the two [18]. Isolation distances should be large enough to achieve the European Union (EU) GM-adventitious-presencelabeling threshold for food and feed, which allows a maximum contamination of 0.9% GM material in non-GM produce [19]
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