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PUBLICATIONS Inside Illinois Vol. 23, No. 3, Aug. 7, 2003

Supersweet sweet corn: 50 years in the making

By Debra Levey Larson
Media/Communications Specialist
College of Agricultural, Consumer and Environmental Sciences

Fifty years ago, sweet corn wasn't all that sweet and had a short shelf-life, which made it difficult for grocery stores to stock it. As a result of the persistence of some UI corn researchers, today's sweet corn not only lives up to its name in taste, it maintains its high quality for more than a week, long enough to get it into stores and onto dinner tables. Jerald "Snook" Pataky, UI plant pathologist in the College of Agricultural, Consumer and Environmental Sciences, has researched the history of UI’s contribution to the existence of today's supersweet corn and will be one of the featured speakers at Agronomy Day on Aug. 21.

The supersweet sweet corn saga began in the early 1950s when John Laughnan, a corn geneticist and UI professor of botany, was investigating the relationship between two genes, one which results in purple pigmentation and another, called sh2, which causes kernels to shrink and shrivel. As he contemplated why kernels of the sh2 genotype were so shriveled, Laughnan discovered that the endosperm of sh2 kernels stored less starch and four to 10 times more sugar than endosperms of normal "sugary" sweet corn or field corn.

In 1953, Laughnan published his work and suggested to the sweet corn industry that his findings might be of use in commercial sweet corn hybrids. At the time, very few sweet-corn breeders shared Laughnan's enthusiasm for the possibilities of this new type of "supersweet" corn.

Despite a lack of support for his ideas, Laughnan began a program to convert a few of the most popular sweet corn inbreds to sh2. In 1961, he released through Illinois Foundation Seeds Inc. (IFSI) the supersweet versions of "Golden Cross Bantam" and "Iochief," which became known as "Illini Chief."

Since seed of "Illini Chief" was difficult to produce, IFSI developed a three-way hybrid named "Illini Xtra Sweet," becoming the first company to sell supersweet corn. The company began to develop markets for the new product in the United States and Japan. For the next 20 years, IFSI and Crookham Co., a family-owned, Idaho-based seed company involved in seed production of "Illini Xtra Sweet," were the only commercial companies with serious supersweet breeding programs. During this time, professors at universities in Florida, Wisconsin and Hawaii also were developing supersweet hybrids.

During the late 1960s and early 1970s, A.M. "Dusty" Rhodes, a UI professor of horticulture, discovered the "sugary enhancer" trait in an inbred line that was developed from a cross of Illinois sweet corn and corn with Bolivian ancestry. This trait modified normal sugary sweet corn, resulting in about twice as much sugar content and extremely tender kernels. Compared with the supersweet hybrids available, these new sugary enhancer hybrids were slightly less sweet but considerably more tender and with a creamy texture missing in the supersweet hybrids. Still, like normal sugary sweet corn, the hybrids had a relatively short shelf-life, because sugary and sugary enhancer hybrids converted kernel sugars to starch after harvest. Supersweet hybrids based on Laughnan's sh2 gene, on the other hand, lacked ADP-glucose pyrophosphorylase, the enzyme responsible for this conversion.

In the early 1980s, Abbott and Cobb Inc., a mid-sized, family-owned seed company, began a successful marketing campaign to educate grocery-store produce buyers and Florida sweet-corn growers about the superior extended shelf-life of supersweet corn. Within five years, the 50,000 acres of sweet corn produced in Florida went from less than 2 percent supersweet to more than 90 percent supersweet. Soon, the same trend occurred throughout the United States for all sweet corn grown for long-distance shipping. Simultaneously, the introduction of a supersweet hybrid with traits necessary for processing marked the beginning of canned supersweet corn, which required no additional sugar or salt added to the can.

Disease resistance has been another factor in the process. In the early 1980s, Rhodes and a student, Mark Mikel, developed a sugary enhancer inbred resistant to the maize dwarf mosaic virus. An inbred line developed this line as a parent of the most widely grown sweet corn hybrid in Europe. Various Rp-genes, which convey resistance to the common rust fungus, Puccinia sorghi, were first identified in the 1960s by Art Hooker, a maize pathologist and breeder at UI. These genes, incorporated into supersweet and sugary-enhancer hybrids, are the primary method by which rust is controlled in sweet corn today. Similarly, Ht-genes identified by Hooker have been incorporated in supersweet hybrids to control northern leaf blight fungus.

In the past three years, Crookham Co., IFSI and a few other companies have introduced a type of supersweet sweet corn that combines the beneficial attributes of Laughnan's sh2 and Rhodes' sugary-enhancer corn. This new corn has the high sugar content and long shelf-life characteristic of Laughnan's sh2 and the creamy texture of Rhodes' corn. Disease resistances identified at the UI also are being incorporated into these new "Xtra Tender" hybrids.

Pataky's history of sweetcorn is one of more than 20 research projects to be featured at Agronomy Day 2003, from 7 a.m. to 2 p.m., Aug. 21 at the Crop Sciences Research Education Center, located south of campus. For more information, including directions and a listing of all of the research projects to be presented at Agronomy Day, visit the Web site: http://agronomyday.cropsci.uiuc.edu/ or call 333-4424.

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