Gene Flow Study in Genetically Altered Crops Helps Progress Transgenic Turfgrass

Genetic improvement of plants through the introduction of a variety of traits — such as tolerance to insects, disease, chemicals, drought or fewer nutrients — is common in agriculture throughout the world. Traditional approaches, such as classical breeding, induced mutagenesis or wide crossing, have a long track record of success. Transgenic technologies, in which genes conferring useful traits of interest are transferred between different species, have been used for genetic improvement for little more than a decade.

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Gene flow is the successful transfer of genetic information between different individuals, populations and generations (to progeny) and across spatial dimensions. It is common in nature and maintains the biological diversity that helps ensure long-term survival of populations and species in variable environments. Typically initiated by pollen dispersal in plants, gene flow is a natural and not inherently adverse phenomenon that occurs in non-transgenic as well as transgenic plants and crops.

Gene flow potential in plants is largely determined by reproductive biology (Table 1). In some species, flowers attract pollinators such as insects or pollen grains are able to travel long distances by wind. In other species, gene flow potential is restricted because their flowers self-fertilize before pollen dispersal. Thus, the reproductive biology of crops largely governs the frequency of outcrossing. Crop reproductive biology can range from almost exclusively self-pollinating to 100 percent outcrossing. Outcrossing frequency typically decreases with distance between the pollen-producing plant and the recipient plant and with the time period between pollen dispersal and fertilization on the recipient plant. Gene flow potential tends to be higher in crop species that have high natural levels of outcrossing. Pollen dispersal, however, leads to true gene flow only if the dispersed pollen fertilizes flowers leading to seed formation and seeds that germinate to produce plants that are competitive enough to reproduce over time. Traits such as herbicide resistance can impart a sizeable selective advantage in locations where the herbicide is used. Under this scenario, there is likely to be a greater degree of gene flow success following the initial pollen dispersal and outcrossing event than in locations where the herbicide is not used.

Table 1: Examples of useful traits being imparted to plants using all available approaches, and estimates of the probable consequences from gene flow1

Physical movement of genetic traits via seeds — such as shattering, wind, water or distribution by animals — or vegetative propagules, including rhizomes and stolons, are not considered true gene flow, but it can be economically important depending on the transgenic crop and production practices. Typically, seed traits such as shattering or movement with air currents that encourage dispersal are not found in most domesticated crops. A number of turfgrasses are propagated by stolons or rhizomes.

Corn, soybean, canola and cotton represent about 99 percent of all commercialized transgenic crop production worldwide. Seed dispersal occurs at a minimal level in all these crops. Outcrossing is limited in soybean, wheat and rice. Canola and corn have greater outcrossing.

The United States also grows transgenic papaya, squash and alfalfa commercially. Transgenics have been produced in other crops/species, but few are presently proceeding through the regulatory process toward commercialization. These include turfgrasses as well as grain crops, vegetables, fruits, ornamental plants, forage crops and trees. Additional species granted nonregulated status or in the process of deregulation or approval include creeping bentgrass, carnation, tobacco, tomato, plum, potato, beet and sugar beet.

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