ISU researchers participate in a national project to further improve the Iowa State University News Service sweet corn

Alan Myers and Thomas Lubberstedt in a cornfield

Alan Myers, professor of biochemistry, biophysics and molecular biology, left, and Thomas Lübberstedt, KJ Frey Chair in Agronomy, are both contributing to a federally funded research project that aims to use advanced genetics and genetic tools to improve the flavor and resilience of sweet corn. Photo by Christopher Gannon. Larger image.

AMES, Iowa – It’s hard to beat fresh sweet corn in the summer. Or is it? Two Iowa State University professors are part of a major federal research project aimed at improving the quality of sweet corn, using the same innovative genetic tools that have led to advances in the corn field.

“Many resources have been devoted to raising field corn. But the effort was much less in sweet corn,” said Thomas Lübberstedt, KJ Frey Chair in Agronomy.

While sweet corn — fresh on the cob, frozen or canned — is one of the most popular vegetables among U.S. consumers, there are economic reasons why research has flowed into the field of corn used for livestock feed, processing, and food production. The $800 million of sweet corn grown in the United States each year represents about 1 percent of the country’s corn production. But Americans aren’t eating enough greens, and consumption of sweet corn, one of their favorites, has been declining for decades. So the US Department of Agriculture’s National Institute of Food and Agriculture funded a research project to improve the flavor and strength of sweet corn.

After launching in 2018, the first few years of the eight-year, $15 million project focused primarily on building the resources behind the work, including a panel of more than 600 genotyped corn varieties for researchers to study, Lübberstedt said.

“This is the backbone of the project,” he said. “Now we’re trying to figure out how to use the information.”

Perfect the beans

Research teams with collaborators from the University of Wisconsin, Washington State University and the University of Florida, the project’s lead institution, are working on various aspects of sweet corn improvement. Alan Myers, a professor of biochemistry, biophysics and molecular biology at Iowa State, is exploring the genetic and biochemical processes that influence how carbohydrates are stored in corn kernels, hoping to increase flavor and texture.

All lines of sweet corn once owed their sugary flavor to a genetic mutation that prevents the glucose that forms in the kernels from crystallizing into an insoluble starch polymer, Myers said. When its kernels are filled with soluble glucose polymers, corn is sweet, juicy, and chewy instead of hard and crunchy. In a second type of sweet corn developed about 20 years ago, the glucose in the kernels doesn’t convert to polymers. This produces a variety of sweet corn often used for freezing and commercial canning, but it doesn’t have the texture of traditional sweet corn.

“What we really want is to combine that nice mouthfeel with a high sugar content,” Myers said.

Myers’ team is studying which enzymes affect the polymer architecture in corn kernels, using tools like CRIPSR gene editing to test the adjustments. While improving quality with an optimal balance of starch and glucose is the main goal, pioneering new methods to grow corn with a sugary snap has an important additional benefit. The currently narrow genetic base for sweet corn leaves the vegetable susceptible to new pest and disease threats.

“Finding several changes in the biochemical process to produce sweet corn would ensure the crop against future challenges. We may never need to go through it, but we want to be prepared” Myers said.

Speed ​​up breeding

Lübberstedt’s group is working on refining the doubled haploid technology to make the rearing method more common in sweet corn. An industry standard for commercial field corn seed production, doubled haploid breeding shortens the process for developing hybrid corn lines from seven to two generations, saving years of time.

The process begins with creating haploids, a version of a plant with only half its usual DNA code, by pollinating a donor with an inducer plant predisposed to produce haploids. The portion of offspring that are haploid, up to 15%, are then treated artificially early in the growth process to double their chromosomes, restoring their ability to reproduce. This creates a genetically pure plant that can be hybridized to create consistent hybrid seeds.

The doubled haploid method holds particular promise for researching genetic gains in sweet corn, as many of the desirable traits — better taste, longer shelf life, disease and insect resistance — can be linked to single genes. In contrast, raising field corn more often appears to increase yield, an outcome influenced by numerous genes and other factors, Lübberstedt said.

“In sweet corn, there are usually a small number of specific genes that you want to preserve, and you can do that with much less effort with doubled haploid breeding,” he said.

Lübberstedt’s group aims to make the method easier to use. One potential improvement is an inducer plant that creates haploids that can be identified by their oil content by automating a process of screening grains typically done by hand based on the intentionally changed color of the haploids. They are also looking at sweet corn varieties with a tendency to spontaneously double, which could eliminate the need to chemically treat young plants to create doubled haploids.

The project is expected to continue until 2025, but the researchers’ work could find its way onto consumer tables before then, Lübberstedt said.

“It is possible that in the coming years what we are developing will be incorporated into new sweet corn varieties,” he said.

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