Breeding for Increased Sweetness in Sweet Corn

Sweetness, a creamy texture and aroma, along with desirable kernel color, good germination, and high yield, are the important traits for sweet corn. Various recessive mutants in corn expressed in the endosperm e.g. sugary1 (su1), sugary enhancer (se), shrunken2 (sh2), brittle1 (bt) etc., which improve quality traits such as sweetness, flavor and nutritive value have been used either singly or in combination for developing new commercial hybrids. In single mutant varieties, at harvest (20 days after pollination), the sugar (sucrose) concentration in su1 and sh2 sweet corn is 3 and 8 times higher than wild type, respectively. For se-type when in combination with su1 the sucrose level is as high as that in sh2. After harvest, the sugar in kernels of su1 and se types is rapidly converted to starch, but this conversion occurs more slowly in sh2 type. However, both su1 and se sweet corn have more phytoglycogen or creamy texture, than sh2 variety without difficulties in germination. The details of breeding methods using a combination of endosperm genes for sweetness improvement are disclosed in the U.S. Patents Nos. 3,971,161 and 4,630,393. To date, two new high sugar types of commercial sweet corn, synergistic and augmented sweet varieties have been developed and released by U.S. seed companies. Synergistic has a combination of su1, se, and sh2 kernels on each ear. It carries the seed quality and vigor of su1 varieties, the enhanced sweet corn flavor of se and harvest-ability and shelf life approaching supersweet (sh2) type. Augmented sweet varieties, sh2 type, carry se modifier genes for tenderness and sweetness and the sh2 gene for high sugars and long shelf life. _____________________________________________________________________________________________________________