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The Maize Page

How was supersweet corn developed?

W. F. Tracy

In the early 1950s, John R. Laughnan was studying alleles at the anthocyanin1 (A1) locus. To aid in these studies he obtained a stock from E.B. Mains of the University of Michigan, in which the recessive allele a1 was very tightly linked to a newly described gene, sh2 (Mains 1948; Laughnan 1953, 1954). In the course of these studies on the a1 locus Laughnan (1953) noted that the kernels of sh2 are unusually sweet and have a pleasant malty flavor. He then carried out extensive studies on the biochemical effects of sh2 relative to both su1 and normal on endosperm carbohydrates. Among his conclusions were the following: sh2 endosperms store less starch than normal and su1 endosperms but in regard to sugars, exhibit approximately ten-fold and four-fold increases over normal and sugary types respectively; most of this is due to sucrose.... Laughnan also noted that the double recessive su1sh2 resulted in even more sugar and less starch. He correctly predicted that the su1 gene acts after sh2 in starch biosynthesis. He also suggested that sh2 would be desirable for the sweet corn industry because of its initially higher sugar content and expected longer shelf life.

To alert sweet corn researchers, Laughnan then published a brief report in the trade magazine The Canner (Laughnan 1954). In this article he discussed the advantages of higher sugar and longer shelf life, plus the very favorable taste test results. We now know Laughnan was correct on these predictions. However, in The Canner article, he was mistaken on one important point. He stated "it is reassuring that representatives of a considerable number of experiment stations and private companies have expressed their enthusiasm over the possibilities which this new finding offers. Soon they will be actively engaged in introducing the new shrunken factor into preferred sweet lines." Whether the people Laughnan mentioned, never started a program on sh2 or started and became discouraged due to poor seed quality and vigor, it was soon clear to Laughnan very few would make a sustained effort.

Laughnan as a research geneticist in the Department of Botany at the University of Illinois could have been expected to discontinue this work at that point. He had done the underlying science, alerted the industry and other researchers to the exciting possibilities, and made his stocks freely available. Furthermore no funding for this type of research was available, and he had major teaching and research responsibilities. But, like many pioneers he saw opportunities where others did not, and perhaps overlooked pitfalls that others saw as unbreachable. Laughnan began a breeding program of his own. He backcrossed the sh2 allele into a number of established sugary inbreds, including P39, P51, Ia453, and Ia5125. The su1 version of P39 X P51 was the famous hybrid `Golden Cross Bantam and Ia453 X Ia5125 made the popular hybrid `Iochief'. After a suitable number of backcrosses, Laughnan had to create enough hybrid seed for evaluation. Since no financial support for this work was available, he planted hybrid seed production blocks on rented land and he and his sons maintained these plots including detasseling the seed parent. He than offered the hybrid seed to home gardeners who received it enthusiastically and was able to have some canned and frozen (Laughnan 1961). In the 13 January 1961 issue of Seed World he announced the release of the Super Sweet counterparts of `Golden Cross' and `Iochief' hybrids and said samples would be available for the 1961 planting season from Illinois Foundation Seeds Co (IFS) (Laughnan 1961). The supersweet `Iochief' became known as `Illini Chief'. The seed of `Illini Chief' was difficult to produce and a three-way hybrid, (Ia453sh2 X P39sh2) X Ia5125sh2 was developed with improved seed production capability. This hybrid was named `Illini Xtra Sweet' and is still sold today. Thus in fewer than eight years from his original suggestion Laughnan had developed a commercially acceptable hybrid, while fulfilling his other responsibilities.

From: History, Genetics, and Breeding of Supersweet (shrunken2) Sweet Corn. W. F. Tracy. Plant Breeding Reviews 14 :189-236

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