The answer is yes and no, depending on the crop. The risk depends if the crop can make fertile crosses with weedy relatives. Some crops like corn and soybean do not have any weedy relatives in the U.S., so the risk is zero. Several other crops have weedy relatives where crop-weed hybrids are known to occur, so there is a risk (Table 1). For 60 crops grown in the U.S., crop-weed hybrids occur for 15 crops and 34 crops have weedy relatives, although it is not well known if they can form hybrids. The remaining 26 crops either do not have any weedy relatives in the world (eg. cotton and corn2) or there are no weedy relatives in the U.S. (eg. soybean). For crops that can cross with weeds, the scientific probability that a GMO gene will escape to a weed is 100%. It’s just a question of time. The rate that the gene might move to a weed depends primarily on the type of pollination. Gene movement is low for self-pollinating plants and much higher for out-crossing plants (Table 2). Other factors also need to be considered like how long the pollen survives, the time of flowering of the crop and weed, how close together the crop and weed are growing. It has also been questioned if GMO gene movement to weeds is even a problem. Obviously, if the gene is for herbicide resistance, the weed would become resistant, a definite problem. The consequences of having other genes moved to weeds are less clear. For example, a gene for a nutritional quality trait likely will not affect a weed’s growth or survival. The potential and consequences of GMO gene movement from crops to weeds needs to be carefully considered as these crops are developed.
| Crop | Weedy relative |
|---|---|
| oat (Avena sativa) | wild oat (Avena fatua) |
| canola (Brassica napus) | birdsrape mustard (Brassica rapa) |
| sunflower (Helianthus annus) | common sunflower (Helianthus annus) |
| rice (Oryza sativa) | red rice (Oryza sativa) |
| sorghum (Sorghum bicolor) | johnsongrass (Sorghum halepense) and shattercane (Sorghum bicolor) |
| wheat (Triticum astivum) | jointed goatgrass (Aegilops cylindrica) (wheat goatgrass hybrids are mostly sterile) |
| Wind pollinated, outcrossing | Animal pollinated, outcrossing | Normally self-pollinating |
|---|---|---|
|
beet |
alfalfa |
oart, barley, wheat |
Source: Keeler, K.H., C.E. Turner, and M.R. Bolick. 1996. Movement of crop transgenes into wild plants. P. 303-330. In: S.O. Duke (ed.), Herbicide resistant crops: Agricultural, environmental, economic, regulatory, and technical aspects. CRC Press.
1 Associate Professor and Extension Weed Scientist, University of Wisconsin College of Agricultural and Life Sciences
2. Corn can hybridize with teosinte, but teosinte is not considered to be a weedy plant.
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