Abstract

The Shrunken2 (Sh2) gene in maize (Zea mays L.) codes for ADP-glucose pyrophosphorylase. Corn homozygous for the shrunken2-reference (sh2-r) allele does not produce ADP-glucose pyrophosphorylase, resulting in greatly reduced starch production and increased sugar in the endosperm. The shrunken2-intermediate (sh2-i) allele produces some enzyme and more starch than sh2-r. The sugary1-reference (su1-r) allele results in endosperm with large amounts of water-soluble polysaccharide (WSP), which gives sweet corn good mouth feel. The combination of endosperm WSP and sugar content determines sweet corn quality. We tested the hypothesis that double mutant sh2-i/sh2-i su1-r/su1-r results in increased amounts of endosperm WSP and sugar than sh2-r/sh2-r Su1/Su1, Sh2-r/Sh2-r su1-r/su1-r, or sh2-r/sh2-r su1-r/su1-r. Carbohydrate content was measured in kernels of near-isogenic inbreds and hybrids of sh2-i and sh2-r in Su1 and su1-r. The lines and hybrids were grown in field trials in 2009 and 2010. Carbohydrate content was determined using enzymatic procedures and quantified with a spectrophotometer. The WSP content in the double mutant sh2-i su1-r was greater than in sh2-r and sh2-r su1-r. Sugar content in the double mutant sh2-i su1-r was greater than in su1-r or sh2-i. The WSP/starch ratio is an important determinant of mouth feel or texture. The sh2-i/sh2-i su1-r/su1-r hybrids had quality factors that exceed both sh2-r and su1-r commercial hybrids.

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