If GMO genes escape, how will the hybrids do?

November 1, 2010

GMOs, or Genetically Modified Organisms, may raise concerns of genes escaping from crops and having unknown effects on natural, wild species. But what is the real risk that traits associated with GMOs will actually migrate to and persist in their wild relatives? Interest in plant ecology, crop production and weed management led John Lindquist and his colleagues from the University of Nebraska and USDA-ARS to investigate how gene flow from a cultivated crop to a weedy relative would influence the ecological fitness of a cropwild hybrid offspring. They published their findings in the recent October issue of the American Journal of Botany.

Grain (Sorghum bicolor subsp. bicolor) is an important food and feed crop throughout the world. The reduced digestibility of sorghum seed relative to other grains makes it a less efficient resource, even though it is highly adapted to growth in semiarid environments common to Africa, India, and the Southern and Western Great Plains of the United States. There has been considerable interest in modifying the quality traits of grain sorghum using GMO technology to enhance its to both humans and animals raised for human consumption.

A major challenge to sorghum producers is the limited number of products available to control weeds within the crop—too many of the common products cause crop damage. To address this challenge, one of the major U.S. seed companies is developing herbicide-resistant grain sorghum using traditional breeding (non-GMO) strategies and plans to deploy them in the United States within the next 5 years.

There is inherent risk in deploying grain sorghum containing novel genes because several related species (e.g., johnsongrass, shattercane) are capable of interbreeding with grain sorghum.

Lindquist and his colleagues focused their research on gene flow between sorghum and its closely related, wild, weedy relative, shattercane (Sorghum bicolor subsp. drummondii). Lack of information on the potential from grain sorghum to shattercane is an important problem because it limits our fundamental understanding of gene transfer and potential hybridization between grain sorghum and shattercane. Their goal was to obtain baseline data using non-GMO sorghum and shattercane that would improve our ability to assess the potential risks of introducing novel genes in grain sorghum into U.S. agroecosystems.

Variation in alleles contributes to the ability of a population to adapt to a variable environment. Yet, this variation is often controlled in cultivated crops for ease of production—for example, with sorghum, all seeds germinate at roughly the same time, plants grow to a uniform height, and seeds ripen at the same time. In contrast, shattercane has seeds with variable states of dormancy, plants that grow taller than sorghum, and seeds that disperse via a shattering mechanism, ensuring dispersal before the sorghum crop is harvested. By crossing shattercane with cultivated sorghum, the authors compared how the crop-wild hybrid performed relative to its crop and wild parents in a number of traits that may be important to its ecological fitness.

By experimentally manipulating temperature conditions, the authors found different germination patterns for the three types of seeds. Although the crop-wild hybrid responded to low temperatures similarly to its wild shattercane parent—both in terms of percentage of seeds that germinated and by staying dormant and delaying germination—it responded to high temperatures similarly to its cultivated sorghum parent; non-germinated seeds of both sorghum and the hybrid died. This may be linked to their seed structures. Shattercane seeds are completely enclosed by glumes, whereas those of sorghum are only partially covered, a factor that makes them much easier to mill but does not protect them well from environmental extremes. The glumes on the hybrids are more similar to sorghum, so it is possible that despite their ability to be dormant, they may not survive well in extreme environmental conditions.

When the authors compared growth factors under natural field conditions, they found that the hybrid grew taller than either of its parent types, had greater leaf area than the shattercane but less than sorghum, and leaf emergence was earlier than in the shattercane. The authors speculate that if the three types were grown in mixture in the field, the hybrid would likely be able to capture more light and thus be more competitive than the two parent types. However, the hybrid produced fewer seeds than either sorghum or shattercane (although they were similar to shattercane at one site).

"Genes from grain sorghum, including a transgene or a traditionally bred specialty trait such as the herbicide resistance traits in sorghum, could be successfully transferred to a weedy shattercane population," Lindquist concludes. Indeed, in this case the relative fitness of the hybrid may be equivalent to that of the wild parent.

However, further research is needed. "It is imperative to know the rate of outcrossing from sorghum to shattercane," Lindquist emphasizes. "In other words, what proportion of seed on a shattercane plant will be pollinated by a nearby grain sorghum population, and how far can that pollen go?"

"Next, we want to be able to predict the overall likelihood that a gene from grain sorghum will enter the weedy shattercane population."

Explore further: To maximize biofuel potential, researchers look for sorghum's 'sweet spot'

More information: Lilyrani Sahoo, Jared J. Schmidt, Jeffrey F. Pedersen, Donald J. Lee, and John L. Lindquist (2010). Growth and fitness components of wild x cultivated Sorghum bicolor (Poaceae) hybrids in Nebraska. American Journal of Botany 97(10): 1610-1617. DOI:10.3732/ajb.0900170

Related Stories

If only the weeds would keep their genes to themselves

October 6, 2009

Family can be a blessing and a curse, and never more so than in the case of crop plants and their wild relatives. These wild and weedy relatives harbor unique and beneficial genes that may no longer be found in their cultivated ...

Sorghum feeds Africa, proves important for U.S. as well

February 2, 2010

(PhysOrg.com) -- Sorghum, a main food crop in many African nations and the second most important animal feed crop in the United States, has the potential for expanded food and fuel uses both here and abroad, said a Purdue ...

Cloned sorghum is aluminum tolerant

February 23, 2010

(PhysOrg.com) -- Leon Kochian and colleagues have cloned a unique sorghum gene that is being used to develop sorghum lines that can withstand toxic levels of aluminum in the soil, a consequence of acidic soils.

Over-the-top grass control in sorghum on the horizon

September 13, 2010

Apply today's chemicals to a sorghum crop for grass control and the sorghum will be killed off also. But a solution could be only a few years away if Texas AgriLife Research plots are any indication.

Recommended for you

A better way to read the genome

October 9, 2015

UConn researchers have sequenced the RNA of the most complicated gene known in nature, using a hand-held sequencer no bigger than a cell phone.

Threat posed by 'pollen thief' bees uncovered

October 9, 2015

A new University of Stirling study has uncovered the secrets of 'pollen thief' bees - which take pollen from flowers but fail to act as effective pollinators - and the threat they pose to certain plant species.

Mapping the protein universe

October 9, 2015

To understand how life works, figure out the proteins first. DNA is the architect of life, but proteins are the workhorses. After proteins are built using DNA blueprints, they are constantly at work breaking down and building ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Nov 01, 2010
Now you just know they're going to screw this up...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.