In the 1900s, scientists began to understand the importance of hybridization, learning to take advantage of hybrid vigor and the crossing of inbred lines. This led to improved hybrids and dramatic increases in corn yields starting in the 1940s.
Today, breeders are turning to genomics to develop better-yielding corn hybrids, where they pursue multiple traits at once and use marker assisted selection and genomes from a diversity of inbred lines to improve varieties.
The challenge, says Dr. Tim Kelliher, principal scientist, reproduction biology with Syngenta in Research Triangle Park, N.C., is to figure out how to use a recurrent selection process to improve corn hybrids based on DNA markers. Kelliher says scientists still have a very rudimentary understanding of yield potential and stress resistance in hybrids.
“We have very well developed varieties for the United States, but we don’t have great varieties for areas that have more challenging agronomics. Understanding genomes by environment and utilizing the tools of genetic modification and gene editing can help us continue to see growth in this area,” Kelliher said at a forum on plant breeding at the North Carolina Biotechnology Center in Research Triangle Park.
Kelliher points out the importance of using haploid plants that only inherited chromosomes from one parent to create inbred lines and this can speed up the process of breeding better hybrids.
“This is useful for breeding. At any point in your breeding cycle, if you want an inbred line, you just induce the haploid state and you end up with a pure inbred line instantaneously,” he explained. “You saved yourself seven years of self- pollination. Instead of going to seven generations of self-pollination, you just go right to the haploid, double it up and then you can start over again.”
Compared to traditional breeding, the use of haploids decreases the breeding cycle from eight years to two years, allowing for faster development of better hybrids that offer increased yields and other desirable traits.
Kelliher also emphasized the importance of genetically modified organisms, or GMOs, for plant breeding, whereby scientists take a desired trait and insert it into the genome of the target, allowing a plant to fight insects or tolerate herbicide sprays. Still, Kelliher said high costs and regulatory burdens are limiting the full potential of GMOs. These limitations makes it difficult to develop GMOs that offer traits such as pathogen resistance and abiotic stress resistance.
In the meantime, Dr. Phil Benfey, co-founder and director of research for Hi Fidelity Genetics in Durham, points out that the big challenge today in plant breeding for corn is further improving hybrid vigor. He says his company is working on developing corn seed with improved vigor.
“For most farmers that we talk to, there’s less concern about having the absolute highest yield every year and much more of a concern of year after year yield stability so you don’t have a year where you are really risking the farm itself,” Benfey said.
The primary cause of year-to-year differences in yield is water availability. And because all of the water for corn comes from the root system, different root systems are able to better acquire water for the plant. “Our goal is to develop corn and other plants with the absolute best root systems,” Benfey said.
“The problem with breeding for better root systems is there is not one root system that fits all. We want to breed root systems that are tailored for the particular environment and particular weather conditions. In order to do that, we need to look at root systems,” he said.
Hi Fidelity Genetics has developed an x-ray imaging tool called “Root Tracker” that allows breeders or farmers to detect root growth in the soil. The tool allows breeders to see what is happening to the roots underground, much like doctors use x-rays to examine parts of the human body that can’t be examined with the human eye. Since breeders now are able to see what is happening to the roots underground, they can develop plant varieties with better root systems, Bentley explained. The better root systems will allow plants to obtain more water.
Hi Fidelity Genetics is focusing its breeding work on early vigor because it's well known that seeds, after they are planted, don’t all emerge at the same time. Benfey points out that the final plant population of corn at harvest is primarily determined during the first 30 to 45 days after planting.
Stand loss may occur due to excessively dry soils, particularly in later-planted fields, where young plants experience moisture stress before their root systems are developed enough to reach deeper moisture in the soil.
“If you plant your corn seed, everything looks fine, then you have a dry period for three or four weeks and some of the plants will die. The difference of who lives and who dies is primarily the guys who have gotten their roots out quicker,’ Benfey said.
Hi Fidelity Genetics has been breeding corn for the past four years and plans to sell seed this year for the 2019 season.