The silk road to better drought tolerance
Those theories about modern corn hybrids being more drought tolerant were put to the test in 2012.
None of them can make grain on no moisture, but some hybrids show incredible resilience with limited moisture. And they get better every year.
Tom Hoegemeyer has spent most of his life studying corn in a part of the Corn Belt that is often short on moisture — Nebraska. He's the grandson of the founder of a longtime family seed business, Hoegemeyer Hybrids, which sells corn and soybean seed in that region. With a doctoral degree in plant breeding, he's now a professor of the subject at the University of Nebraska.
It's the silks
He says part of the secret to breeding corn that can withstand prolonged drought is in diverting the limited moisture to the right parts of the plant. While you might think the tassel needs most of the moisture to ensure good pollen shed and seed set when it is hot and dry, you'd be wrong. To make corn, it's the ears that need the most moisture, particularly the silks, even if the plant is stressed.
“We have plenty of pollen,” says Hoegemeyer. “It doesn't take pollen from many plants to pollinate an entire acre, if it's well distributed.”
Rather, he says, drought-tolerant corn must divert water from the tassel, stalks, and leaves to the ear, particularly to the silks that capture pollen to make a kernel of corn.
“Silks are 98% water,” says Hoegemeyer. “If you are short on moisture at pollination, some of the silks don't elongate and don't capture pollen to carry to the kernel site. No kernel embryo forms.”
In this case, you get ears with partial kernel fill. The visible sign of that is drought-induced tipping back from the end of an ear, or the side-of-ear zippering effect on small ears.
“Drought-tolerant corn hybrids are selected for multiple genes that allow for better silking,” he says. “They partition more water and sugar flow to the silks and developing kernels.”
The misconception is that it's the tassel and pollen shed that suffer the most in a drought. Hoegemeyer says most pollination in corn takes place before 10 a.m. — before the hottest part of the day.
The critical stages
Corn has several vulnerable stages when severe stress (such as drought) can significantly impact yield.
The first is early, during the six- to eight-leaf stage. “That's when ear diameter is determined — whether it will have 18 to 20 rows around it or 12 to 14 rows,” Hoegemeyer says. This happens at a point in the season when there is good soil moisture and there are cooler temperatures.
The second critical stress time is 10 days before to 10 days after pollination. If the plant has good moisture and good sugar availability to the kernels, you will get longer ears and better fill to the tip.
The final critical period is the grain-fill period after kernels are set. Selecting corn hybrids that are superior in grain fill is hard work; you have to measure it as it progresses following kernel set.