The potential exists for new types of invasive species to emerge with introgressed genetic material from trans-genic crop species transferred to related native or invasive species. Transgenic sunflowers (hybrids ofnative and transgenic Helianthus annuus) are often found adjacent to genetically modified (GM) sunflower fields because of genetic introgression. Only a few studies have been conducted to determine if transgenic weeds pose a threat similar to that of invasive species. In one study, transgenic oilseed rape, potato, maize, and sugarbeet were no more invasive or persistent in fields and natural areas than the traditional crop species. However, 42% of native sunflower populations adjacent to GM sunflower fields are transgenic hybrids, and these genes persist in these trans-genic weed populations for at least five generations. Transgenic traits for disease, insects, or herbicides could give a competitive advantage to wild species, thereby conferring a higher level of invasibility to these transgenic weeds. Transgenic traits could also be transferred to endangered species, in a situation paralleling the genetic erosion of cutthroat trout populations in the White Mountains of Arizona (see the section titled 'Hybrid species with introgressed genes'). The consequences of the presence of transgenic weeds in crop or natural plant communities will depend on their fitness, ability to spread, level of the genetic erosion of the populations of native species, and their overall ability to displace other species as invasives in natural communities.
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