Farmers who plant corn for silage, snaplage or grain are continually seeking hybrids that best suit the growing conditions on their farms. When weather conditions allow timely spring planting, corn reaches between nine and 12 feet at maturity and farmers anticipate high yields.

While traditional corn yields well, it often presents challenges throughout the season including difficulty clearing plants for herbicide and fertilizer applications and lodging following early autumn wind and rain.

Growing short corn may not be the goal of most farmers, but Corrie Hopkins, Bayer Crop Science, explained the evolution of higher quality corn and the performance potential for short corn. Hopkins addressed farmers at the annual Keystone Crops & Soils Conference hosted by PennAg and Penn State.

In the late 1800s, the average corn yield was around 0.8 bushels/acre. “In 1918, we started to use hybrid methods for corn breeding,” said Hopkins. “By the 1940s, farmers saw new technology and chemicals, including 2,4-D. We saw more hybrids, and farmers realized they could use hybrids instead of open pollinated varieties. There was also a split between public and private breeding programs. At the time, universities were working with germplasm and hybrid breeding companies started to sell their own varieties.”

When a single-cross corn hybrid was introduced during in the 1960s, farmers saw a true bump in yields. “Molecular markers were identified in the 1970s and are used heavily today,” said Hopkins. “Then we saw traits such as Roundup Ready® and Bt-corn. The corn genome sequencing was completed in 2008 and now we have gene editing.”

Science has made significant genetic gains, but what else is coming? Hopkins, a trained geneticist and a self-described breeding nerd, talked about the genetics of the double-cross hybrid method that involves first generation hybrids from two single crosses.

“We didn’t have detasseling in the big production fields and they didn’t have the mechanical ability to use a single cross seed [back then], so they crossed those again and got more seed out of it,” said Hopkins.

Performance data from the 1960s indicate that farmers and breeders thought they were doing well when they saw significant yield boosts. Why was the yield increase higher in single-cross hybrids compared to double-cross hybrids?

“Because there is more response in hybrid vigor in the initial cross,” said Hopkins. “It’s also referred to as heterosis, which is increased function of any biological system with hybrid offspring.” Heterosis allows the crossing of genetically distant parents and results in higher genetic variation. However, breeders in the early 1900s found inbreeding depression due to continually open pollinating the same genetics.

Although there are many seed companies and thousands of corn varieties available today, all corn seed traces back to seven progenitor lines. “Within a breeding program, you want to cross two different heterotic groups, as genetically different as possible, so you get the best hybrid vigor possible,” she said. “Three major seed companies scooped up 90% of the germplasm still being used today.”

Hopkins noted that the U.S. Plant Variety Protection Act of the 1970s encouraged private companies to develop new varieties that would be available to the public.

How does genetic gain continue? The most recent improvements in corn resulted from wheat research. Plant pathologist Norman Borlaug developed a high-yielding wheat variety, but it was so tall it fell over. Borlaug then produced a high-producing dwarf wheat variety with improved standability.

Hopkins said the dwarfing mutation has been present for a long time. Over 40 dwarfing genes have been identified, but dwarf corn varieties were sometimes sterile with short ears and tasseling issues.

Short stature corn matures at about five to seven feet. “With short corn, only growth below the ear is affected,” said Hopkins, explaining the rachitic trait, or shortening of internodes. “Anything above the ear is not affected, which means ears and tassels are not affected, so there are no sterility issues.”

Shrunken internodes and leaf collars tend to stack a little closer. “There should be the same amount of residue because the leaf collars are the same,” Hopkins said. “None of the leaf matter has changed. There will be less stalk matter.”

Short stature corn has stronger stalk strength, which helps plants remain intact in heavy wind. Because plants aren’t using energy for upward growth, roots can expend energy to move downward. “We see much more soil exploration by roots,” said Hopkins, adding that short corn might survive better in drought conditions.

“Standability will always improve yield,” she said. “If half of tall hybrids go down in a storm, we’d have an advantage with short corn. If the short stature corn is planted at the same population as a tall hybrid, they’re going to perform just as well. Farmers won’t have to plant short corn at a higher population to reach yield potential – short corn planted side by side with tall corn should be able to plant at 33,000 and yield should be within a bushel.”

With shorter corn, farmers will have better field access throughout the growing season for fertilizer and other treatments. There’s also reduced lignin content because stalks are shorter.

“There’s the same amount of leaf matter, but not as much stalk,” said Hopkins. “We see reductions in ash, undigestible fiber and overall lignin percentage – this translates to better silage quality.”

Ongoing feed studies are comparing dairy cow performance on short stature vs. full height corn. Trials are also aimed at determining whether short stature corn will cross well with BMR corn, which might eliminate some of the agronomic issues associated with BMR as well as improve standability and possibly improve disease resistance.

Research is continuing to work on nutrient management and how much it can be pushed. Roots are reaching more deeply so it may be possible to reduce fertilizer use.

“Getting farmers to change to a 20-inch planter might be a battle we keep fighting,” said Hopkins. “But short corn doesn’t have to planted at a higher population to get good yield. You don’t have to change management if you don’t want to. Farmers know what their fields can yield. It’s a matter of bridging the gap between the prescriptive plan and what the farmer thinks they should do and working out the details.”

by Sally Colby