Endosperm Carbohydrates and Debranching Enzyme Activity in Five Native sugary1 Alleles in Maize

The su1‐ref allele, the only mutant used in sweet maize ( Zea mays L.) until the 1960s, continues to be used in sweet maize improvement programs. Wild‐type Su1 encodes the starch debranching enzyme (DBE) isoamylase1 (ISA1) that is required for amylopectin production. Loss of Su1 function also leads to a reduction in activity of another DBE enzyme, pullulanase. Five naturally occurring su1 mutations have been identified and characterized as having different carbohydrate compositions. The alleles have not been evaluated for isoamylase and pullulanase DBE activity or for mature kernel composition of hybrid allele combinations. The five su1 alleles were backcrossed into two field corn lines, A619 and A632. The resulting inbreds were crossed in a factorial design. The hybrids were grown in 2015 and 2016 in Madison, WI, for an evaluation of mature kernel composition. In 2016, the su1 inbreds were grown and immature tissue was harvested 21 d after pollination for enzymatic analysis. Significant differences were identified among the su1 hybrids for starch and water‐soluble polysaccharides (WSP). Hybrids containing the su1‐p allele consistently accumulated the greatest amount of starch and the lowest amount of WSP, and those with the su1‐ne allele had the lowest amount of starch and greatest WSP content. No significant differences were observed among the su1 inbreds for isoamylase or pullulanase activity. Little to no isoamylase activity was observed, whereas pullulanase activity was reduced among the su1 mutants compared with the wild type, Ia453‐ Su1 . Our data indicated that differences in starch and WSP observed among the su1 alleles was not due to isoamylase or pullulanase DBE activity.