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Gene flow in alfalfa: Distance needed at different thresholds

Sandya Kesoju for Progressive Forage Published on 28 September 2017
Alfalfa alkali bee in touchet-Gardena area

Genetically engineered (GE) alfalfa was deregulated in 2005 for the first time and again in January 2011, opening the door to renewed commercial sales and planting.

Acreage planted to GE, Roundup Ready alfalfa has rapidly increased since deregulation in 2011. In 2013, to assess adoption rate, we surveyed 530 hay and seed producers in three major alfalfa production areas in the western US. Eleven percent of growers had grown GE hay, seed or both during the first period of deregulation and 22 percent after the second deregulation.

In Washington state, alfalfa is an essential, high-value rotational crop that contributes significantly to farm income, soil health and sustainability.

Concerns over the coexistence of GE, non-GE or conventional and organic alfalfa are acute in Washington state because of strong export demand for non-GE alfalfa hay, growing demand for organic hay and alfalfa-based feed supplements, and deep-set divisions in the agricultural community and public over the impacts of GE technology and the distribution of costs, benefits and risks.

Planting GE alfalfa has already triggered trade repercussions in Washington state. A shipment of 2013 non-GE alfalfa grown near Royal City, Washington, was found to contain a low level of the Roundup Ready gene and had to be diverted to a domestic market.

The occurrence increased concern and scrutiny over the presence of the Roundup Ready gene in Washington alfalfa and led to increased testing and marketing costs. Given that a significant and growing share of Washington production is destined for GE-sensitive markets, such costs are of concern to farmers and the industry.

At present, a majority of the markets the U.S. exports alfalfa to are GE-sensitive. Therefore, seed companies are offering seed lots which say “nondetect” – a lot that has GE traits at a rate of 0.1 percent. They are also offering adventitious presence-sensitive certified seed. Some companies charge extra money for testing the seed while other companies don’t.

Most GE-sensitive export markets are willing to accept the presence of the Roundup Ready gene at levels up to 0.9 percent. The general expectation is that the level of adventitious presence in the non-GE seed is likely to carry over into the forage harvested from the planted field at or above the level in the seed.

Accordingly, the closer the level of adventitious presence in the seed is to 0.9 percent, the less room farmers have to allow for unpreventable gene flow or any other source of contamination. Consequently, growers in areas that export hay have been proactive in developing coexistence practices.

However, understanding alfalfa gene flow is complicated since alfalfa is largely a cross-pollinated crop and pollination is carried out by insects, namely bees. Commercially produced alfalfa seed is pollinated primarily by managed pollinators, typically honey bees, alfalfa leafcutter bees and alkali bees. Wild bees such as bumblebees also pollinate alfalfa.

In response, industry developed seed production isolation distances that take into account the bee pollinators used and market class (i.e., adventitious presence-tolerant and adventitious presence-sensitive). The studies used to develop coexistence strategies have been largely limited to research-scale experiments using either honey bees or alfalfa leafcutter bees.

However, no landscape-scale studies have been conducted to validate industry standards. Therefore, my colleagues and I were interested in quantifying the extent of gene movement from GE seed fields to commercial conventional seed fields on a landscape level to provide the industry with information to support coexistence strategies.

This study was coordinated with Stephanie Greene, a USDA-ARS scientist with the Plant and Animal Genetic Resources Preservation Research Unit at Fort Collins, Colorado, and Ruth Martin, a USDA-ARS scientist with the Forage Seed and Cereal Research Unit at Corvallis, Oregon.

We measured adventitious presence in conventional seed fields located at different distances from GE seed fields and with the help of Matt Kramer, a USDA-ARS statistician in Beltsville, Maryland, we predicted the maximum distance between GE and conventional alfalfa seed fields that lead to adventitious presence levels of less than 0.1 percent, 0.5 percent and 0.9 percent in conventional fields.

We picked 0.1 percent, 0.5 percent and 0.9 percent as threshold levels because industry has established less than 0.1 percent as a nondetect standard, and individual seed companies have adopted thresholds ranging from 0.1 percent to 0.9 percent. We used a 95 percent cutoff since most of our samples were from the field edge, thus estimated distances for the cutoff would be conservative.

The Walla Walla Valley and Columbia Basin in Washington state are important alfalfa seed-producing areas. In 2013, we mapped GE and conventional seed fields located in the Touchet-Gardena area of the Walla Walla Valley in Washington state and Oregon. The Touchet area has been designated a GE-grower opportunity zone where both GE and conventional alfalfa seed is produced.

GE seed fields and conventional seed fields were identified that were located at various distances, the farthest being 7 miles from GE sources, the closest being 10 feet. The primary pollinators used by growers in this area are alfalfa leafcutter bees and alkali bees.

Alkali bee bed in touchet-Gardena area

Alfalfa leafcutter bees are placed in the field during mid-May to July while alkali bees, which are ground-nesting bees, are found active from mid-June to mid-July.

We harvested the edges of conventional fields using a combine or by hand, sampling every 100 feet and within fields for every 50 feet. Parent seed lot samples of the 2013 harvest were collected for conventional fields to measure the occurrence of adventitious presence in parent seed lots.

Sandya Kesoj, Jeff Colson and Jesus Prieto harvest alfalfa seed fields

We found adventitious presence of 0.23 percent or lower in the parent seed lots used to plant the conventional seed fields sampled. Therefore, the first and most important step for growers is to plant seed tested and determined as non-GE or adventitious presence-sensitive certified seed if they are exporting to GE-sensitive markets.

Isolation distances were estimated using adventitious presence data from conventional fields.

When threshold levels were set at 0.9 percent adventitious presence, the isolation distance needed between conventional and Roundup Ready fields was 1,083 feet (0.21 miles). At 0.5 percent and 0.1 percent adventitious presence, the distances were 1,975 feet (0.37 miles) and 8,009 feet (1.52 miles). Overall, field adventitious presence would likely be lower than our established thresholds since field edges were sampled.

Our estimates of isolation distances were greater than current industry coexistence standards for conventional seed lots, but fell within the range recommended for adventitious presence-sensitive seed production. Current coexistence standards may need to be adjusted when alkali bees are used as pollinators.

Seed producers can use our research results to determine appropriate distances from Roundup Ready seed fields depending upon the market they are targeting. Our research supports the effectiveness of industry efforts to set up adventitious presence-sensitive grower opportunity zones, since these zones effectively reduce the source of GE pollen in the landscape, thereby sidestepping the difficulty of developing isolation distances.

Although to estimate isolation distances in Walla Walla required satisfying three levels of adventitious presence in 95 percent of our samples, we also learned that adventitious presence is influenced by other variables, which makes it difficult to adopt a one-size-fits-all isolation distance even within a single valley; however, distance was the most important factor in limiting the movement of the gene into conventional seed fields.  end mark

PHOTO 1: Alfalfa alkali bee in Touchet-Gardena area of the Walla Walla Valley, Washington. Photo by Sandya Kesoju.

PHOTO 2: Alkali bee bed in Touchet-Gardena area of the Walla Walla Valley, Washington. Photo by Sandya Kesoju.

PHOTO 3: Sandya Kesoju, Jeff Colson (driving the tractor) and Jesus Prieto harvest alfalfa seed fields along the field edges and in between the fields at Touchet-Gardena area of the Walla Walla Valley, Washington. Photo by Dr. Stephanie Greene.

Sandya Kesoju is the director for agriculture education, research and development at Columbia Basin College. Email Sandya Kesoju.