Characterization of Five Naturally Occurring Alleles at the Sugary1 Locus for Seed Composition, Seedling Emergence, and Isoamylase1 Activity

Abstract

The mutant su1‐ref allele is of interest in the commercial sweet maize (Zea mays L.) industry. It was the only starch synthesis mutation used for sweet maize until the 1960s and is still used today, especially in combinations with other loci. The wild‐type Su1 allele produces a starch debranching‐type isoamylase, ISA1, required for normal amylopectin and starch granule crystal formation in maize endosperm. Five naturally occurring mutant alleles have been identified at the su1 locus, but they have not been characterized for seedling emergence, field traits, mature kernel composition, or ISA1 enzyme activity. These five alleles were backcrossed to A619 and A632, two modern field maize inbreds. The su1 inbreds and wild‐type checks were grown in El Monte, Chile, in 2009 to 2010 and Madison, WI, in 2010 to 2011 for seed production to evaluate seedling emergence, field traits, and mature kernel composition. In a greenhouse in Madison, WI, in 2011 to 2012, the su1 inbreds were grown and kernels were harvested at 20 d after pollination (DAP) for enzymatic analysis. Significant differences were identified among the su1 inbreds, where su1‐ne was consistently poorer for emergence and field traits and the su1‐pu allele was consistently better than the other su1 mutant alleles for the evaluated traits. Differences were observed in the presence of ISA1 enzyme; however, no functional ISA1 enzyme activity was observed. Further research is necessary to elucidate the differences for appearance, carbohydrate composition, and seed germination and emergence traits in lines with no functional ISA1 enzyme activity.