Reprinted with permission from Miner Institute, written by Eric Young
Today’s corn hybrids come with an array of traits. Corn traits are specific growth attributes and come from traditional breeding methods, genetic engineering, or both. The culmination of many years of traditional breeding combined with today’s genome sequencing and genetic engineering tools give growers a lot of options in the field.
Traits derived from more traditional breeding include grain yield, stover yield, starch content, disease resistance, vigor, and fiber digestibility. Traditional breeding (e.g., crossing inbred plants) is largely responsible for the increases in corn yield over the past century due to improved agronomics and stress tolerance.
Fiber digestibility often varies little among conventional hybrids grown in the same environment and harvested at the same time. The one big exception of course is brown midrib hybrids (BMR), which are typically 30% lower in lignin content (and 8 to 10 % greater in NDFD) compared to non-BMR hybrids. The BMR trait is from a random mutation discovered in 1924 ─ it is all natural, no genetic modification needed.
Genetically engineered (GE) traits can be thought of as further refinement of the corn genome. The most important GE corn traits on the market are for herbicide (e.g., glyphosate tolerance or Roundup Ready) and insect resistance (e.g., Bt hybrids). These traits are the result of inserting a specific “foreign” gene into the maize genome.
For example, Bt stands for Bacillus thuringiensis, which is a soil-dwelling bacteria from which the DNA is borrowed to put into a hybrid’s genome. When this gene is expressed in a corn plant, a protein is produced that acts as an insecticide to several insects in the Lepidoptera family (moth and butterfly caterpillars). Specifically, Bt hybrids produce crystalline proteins (referred to as cry-proteins) that cause gut lesions in certain caterpillar pests when ingested. Without this ingenious invention, many farmers would still need to rely on chemical insecticides to control these insects.
There are several different Bt traits available on the market. A given Bt trait is referred to as an “event” and corresponds to a specific combination of proteins that target a specific insect pest such as corn rootworm or corn borer. Multiple Bt events are used in some hybrids to reduce the risk of the insects developing resistance.
What about other confusing corn terminology like “leafy”, “floury”, and “triple stack”? The term “leafy” refers to a genetic trait that results in a greater number of leaves above the ear. The idea was that the more numerous leaves would lead to better overall growth and quality. Floury is also a genetic trait, a newer term referring to the type of endosperm in the kernel and the quality of the starch. Triple stack hybrids are GE hybrids that have three distinct GE traits. A common triple stacked hybrid would have glyphosate tolerance, a Bt event for corn rootworm, and a Bt event for corn borer.
Learn more about Bt corn at: http://www.ext.colostate.edu/pubs/crops/00707.html.
