23, No. 3, Aug. 7, 2003
Supersweet sweet corn: 50 years
in the making
Debra Levey Larson
College of Agricultural, Consumer and Environmental Sciences
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"
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
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:
or call 333-4424.