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Breeding Versus Engineering to Make Drought Tolerant Corn

How genomic technology helps advance crop improvement

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Breeding Versus Engineering to Make Drought Tolerant Corn
Wmpear via Wikipeadia Commons

Although too late for 2012's record dry spell, drought-tolerant corn is finally coming to the market. Seeds for corn hybrids that can survive longer periods of water deprivation are now, or will soon be, available from Syngenta, Pioneer, and Monsanto. The differences in how the corn strains were developed provide an insightful example of the practical impact that years of researching and analyzing the genetic code of different organisms—genomic science—has had on modern agriculture.

Traditional Plant Breeding Meets Genomics

Syngenta's Artisian and Pioneer's AQUAmax corn strains were developed using a high-tech version of traditional breeding. Instead of genetic engineering, both Pioneer and Syngenta relied on advanced genetics and breeding approaches based on molecular genetics to develop the Artisian corn hybrids.

The companies combined proprietary genetic information derived from strains they developed over many years of breeding with current genomic data, such as that obtained from the whole corn genome sequence which was completed in 2009, to identify many dozens of native corn genes associated with drought tolerance. Through selective crossbreeding these drought-resistance genetic markers were selected and brought together in a single plant. The result produced a hybrids with pronounced drought tolerance.

Some of the traits altered by the breeding that improved drought resistance could be identified, such as a reduction in the size of the stomata in the corn. However, with this sort of breeding approach, many of the physiological traits affected by the drought-associated genes are simply unknown. A specific gene may have been correlated with increased drought tolerance in certain plant strains, but it is unknown what the gene actually changes in the plant to increase this tolerance.

Genetic Engineering Complex Traits

Monsanto took a different route to develop DroughtGard corn by using genetic engineering to add a gene that bacteria use to continue growing in cold environments. This cold shock gene helps maintain production of growth proteins and, when in corn, it help prevent shriveling during low water periods so that the plants can flower and produce kernels.

Monsanto's DroughtGard corn marks the first commercial crop genetically modified to enhance growth and survival traits in response to environmental stress, in this case, periods of low water availability. Previous genetically engineered traits primarily conferred pathogen, pesticide, or herbicide resistance, which are more straightforward characteristics to introduce. While resistance to a chemical pesticide or herbicide can usually be conferred by introducing a single new gene, creating a plant that can thrive in a challenging environment may require altering many traits controlled by many genes.

Approval Requirements for Introducing Genetically Engineered Plants

Since the Syngenta and Pioneer hybrids are derived from corn strains previously engineered for herbicide resistance, they are, in fact, genetically modified. It is just that the drought tolerance was not introduced using this technology. However, since the genetic modifications in the parental strains were previously approved, the new drought resistant hybrids from these companies do not require USDA approval process before releasing to the market.

Monsanto, on the other hand, had to prove it to the USDA that its corn strain engineered with the bacterial cold shock protein posed no environmental or agricultural risk. Monsanto obtained this release at the end of 2011. The company is waiting for final approval in a few other regions outside the US which it hopes to receive before launching the seeds in 2013.

Genetic Engineering vs. Breeding

Monsanto's DroughtGard actually demonstrates the difficulty of genetically engineering a plant to manifest a complex characteristic such as drought tolerance. In fact, the ability of the Monsanto cold shock engineered corn to thrive in drought conditions is not markedly different from Pioneer's or Syngenta's bred corn.

Some groups suggest the similarity in the results of these first generation drought tolerant plants indicates that it is better to use techniques other than genetic engineering to improve growth stress tolerance. However, it rather appears to more strongly suggest that these traits are complex and are best cultivated by multiple approaches. Since two independent genetic approaches generated corn strains with similar resistance to drought, the combination of these approaches may produce an even heartier variety.

(Posted: Sept 7, 2012)

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