Gene Flow Study in Genetically Altered Crops Helps Progress Transgenic Turfgrass

Gene flow in a larger context

Gene flow is only one of several mechanisms by which plants or seeds become intermixed at low levels with other plants or seeds where humans did not intend them to be. This type of unintended mixing occurs with both transgenic and nontransgenic plants and crops. Other mechanisms include inadvertent physical dispersal or mixing of seed, quality-control failures and inevitable human mistakes. Low or trace levels of commingling via all of these mechanisms is virtually unavoidable in commercial-scale plant production. Thus, requirements for unrealistically low occurrence of unwanted substances, such as transgenic seed, can lead to progressively higher overall costs to industry and consumers without a measurable benefit.

Quick Tip

Gene flow from transgenic crop plants to weedy or wild relatives can be an issue if they are sexually compatible. Thus, one way to view gene flow issues in a global context is from the perspective of the important worldwide food/feed crops and the weedy or wild species with which they are sexually compatible. About 200 plant species account for essentially all of the significant economic activities for humans worldwide, and approximately 10 percent of these account for almost all of the human caloric consumption. Among the world's worst weed species, only five groups — related weeds of rice, sorghum, rapeseed, sugarcane and oats — are sexually compatible with the most important crops. The potential for gene flow between crop and weed species might not become actual gene flow due to differing habitats or geographic distribution, genetic barriers to outcrossing, etc. The number of combinations of transgenic crop/weed or transgenic crop/non-transgenic crop that are likely to develop highly troublesome gene flow problems is quite small globally. Problems with particular weed or crop species, however, could occur locally or regionally for certain traits conferred by transgenes.

The biology of the transgene trait will largely determine consequences of gene flow to sexually compatible nontransgenic crops, weeds and wild relatives. Outcrossing from herbicide-tolerant transgenic crops can produce progeny that is highly favored in areas where the particular herbicide is used, but not in other areas. However, ordinary selection pressure from repeated herbicide use in herbicide-resistant crops may lead to a greater development of weed resistance (in the absence of gene flow) than gene selections attributable to gene flow between the crop and weed.

Importation of weeds or other plants from foreign lands is an historic problem, but instances in which fully domesticated crops have become weed nuisances are rare. The chances that transgenic modification of a single trait in a domesticated crop would change the crop into a successful weed also is low, and gene flow from the majority of transgenic crops probably will have minimal ecological impacts outside of agricultural areas.

Quick Tip

Transgenes that confer tolerance to stresses — such as drought, diseases, insects and salty soil — might require different or additional evaluation because gene flow into nontransgenic crops or weedy relatives can provide selective advantages in both agricultural and nonagricultural settings.

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