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Roadside alfalfa: Innocent bystanders or conveyers of genetically engineered traits?

Stephanie L. Greene for Progressive Forage Grower Published on 30 March 2016
Dr. Sandya Kesoju sampling roadside alfalfa

Clumps of alfalfa are a common sight along roads and vacant lots in areas that grow alfalfa for hay or seed.

Although these stands contain relatively few plants compared to fields of alfalfa, the fact that bees ferry pollen into adjacent seed fields has long prompted the alfalfa industry to develop best management practices that control roadside plants to ensure varietal purity.

Management practices to ensure seed purity have become even more important since the commercialization of genetically engineered (GE) alfalfa. Alfalfa genetically engineered to be resistant to glyphosate was available to growers briefly from 2005 to 2007.

In 2011, glyphosate-resistant alfalfa received final approval for commercial production, and in 2014, GE low-lignin alfalfa was deregulated and will be available in the near future. Now that GE alfalfa is widely available, strict adherence to management practices is prudent, since inadvertent contamination of conventional seed lots can result in the adventitious presence of the GE trait (transgene) in hay and seed bound for export or organic markets.

These markets have a low tolerance for genetically modified organisms (GMOs). Considering that China has recently rejected hay grown in Washington due to GMO presence, the concern is real.

So what role do feral roadside plants play in dispersing transgenes? Is there a risk that transgenic feral plants serve as reservoirs or conduits that might facilitate the movement of transgenes into conventional alfalfa? Are there environmental and agricultural factors that influence feral plant occurrence and, importantly, transgenic feral plant occurrence? My colleagues and I were interested in answering these questions.

Ruth Martin is a USDA-ARS scientist with the Forage Seed and Cereal Research Unit at Corvallis, Oregon, and Sandya Kesoju is a research associate with the Washington State University Irrigated Agriculture Research and Extension Center in Prosser, Washington.

Alfalfa seed production areas in the United States

In 2011, we conducted a roadside survey in Fresno County, California, Canyon County, Idaho, and Walla Walla County, Washington – three important alfalfa seed-producing areas. We travelled 6,000 km (more than 3,700 miles) of rural roads, stopping at 4,190 random sites to look for feral alfalfa plants.

We found 185 sites with feral plants. We also found an additional 219 sites with feral plants as we visited our random sites. At each site, we collected leaf and seed samples and took notes on the environment.

With the help of Matt Kramer, a USDA-ARS statistician in Beltsville, Maryland, we examined the occurrence of feral plants in relation to environmental and agricultural factors. We also examined the occurrence of transgenic feral plants in relation to the location of original glyphosate-resistant seed fields.

Mark McCaslin, vice president of research at Forage Genetics International, provided this data. Monsanto Inc. also provided us with data regarding how far the closest glyphosate-resistant hayfields (fields grown during the first period of deregulation) were to our feral populations.

Generally, feral plants were rare. Across study areas, 4.4 percent of our random sites contained feral populations. The greatest number of sites with feral plants was observed in Fresno County, California, and the fewest in Canyon County, Idaho. Unfortunately, none of the variables we examined appeared to influence where feral plants occurred.

This included environmental variables such as slope, aspect and elevation, and climatic variables such as temperature and precipitation. Roadside habitat and surrounding crops also did not predict the occurrence of feral plants. This was not particularly surprising considering that alfalfa seed can readily escape from combines, planters, seed bins and even transported hay.

Also, alfalfa is sometimes included in seed mixes used to re-vegetate roadsides and rangeland, and volunteer alfalfa plants may persist along the edge of fields if care is not taken to remove the entire stand.

When we factor in alfalfa’s natural propensity to establish and persist wherever conditions are right, and that seed dormancy allows seedlings to emerge over time from the soil seedbank, it’s not surprising how tough it was to pinpoint specific variables that influenced feral plant occurrence.

We found that size of roadside stands varied, with the largest populations in Canyon County and the smallest in Walla Walla County.

Forty-eight percent of the feral populations consisted of plants at different ages, suggesting that many populations are self-sustaining. The spatial distribution of roadside stands suggested plants on some sites could be colonizing a nearby site.

Stands were generally close enough that bees could fly between them. Although feral plants were rare, they were readily found in seed and hay production areas, and multiple lines of evidence suggested they can serve as conduits for transgene movement.

After testing leaves and seeds, we found transgenic feral plants in all three counties. In Fresno County, 32.7 percent of sites having feral plants had transgenic feral plants. In Canyon and Walla Walla counties, we found 24.7 percent and 8.3 percent of feral sites had transgenic plants.

In Fresno and Canyon counties, we tended to find transgenic feral plants at locations where the probability of seed escape was high, such as adjacent to original GE seed fields or on roads used to transport GE seed to conditioning plants.

It’s interesting to note that when we surveyed 530 alfalfa producers, only 2 percent of respondents felt risk of seed escape was “highly likely.” Hopefully, our study will help producers understand how readily alfalfa seed can escape during planting and harvesting.

In Fresno County, transgenic feral plants tended to occur more frequently farther away from the single historic seed field, while in Canyon and Walla Walla counties, transgenic plants tended to be more frequent as we moved closer to historic GE seed fields.

Our results in Fresno County were puzzling at first. Although there had been only a single GE seed field, we found almost twice as many transgenic plants as the next-highest location.

A possible explanation may be that the state highway department sprays roadsides with glyphosate (roadside sprays in Idaho and Washington used a combination of glyphosate and 2,4-D) and that transgenic plants are being inadvertently selected. Another possibility is that large amounts of GE hay were planted in our Fresno study area during the first deregulation.

Based on the GE hay information made available to us, we were not able to determine if GE hayfields influenced the occurrence of transgenic feral plants, in either Fresno County or our other study areas.

Our study confirms that alfalfa has joined oilseed rape as a GE crop where transgene dispersal has occurred beyond fields into roadside populations. Still to be determined are the ecological and economic consequences of transgenic feral alfalfa plants. We were unable to detect adventitious presence in conventional seed fields adjacent to transgenic feral plants in Fresno.

However, if grower adoption rates match those of GE cotton, soybean, corn and oilseed rape, the occurrence of transgenic feral populations will increase, and negative consequences may become evident at some point.

To ensure the coexistence of neighbors growing alfalfa for GE, non GE and GE-sensitive markets, all producers should be concerned about minimizing GE seed spillage and controlling feral plants.  FG

PHOTO: Dr. Sandya Kesoju sampling roadside alfalfa plants in Fresno County in 2013. Note that the roadside has been sprayed with glyphosate. Photo courtesy of Stephanie Greene.

Stephanie L. Greene is with the Plant and Animal Genetic Resource Preservation Unit of the USDA – Agricultural Research Service. Email Stephanie L. Greene.