Effect of dosage at the soft starch (h) locus on starch granule volume in maize

Larger particle volume is beneficial for many aspects of maize starch processing, and may improve the performance of some starch attributes. Of the numerous endosperm carbohydrate mutants, the soft starch (h) mutant appears to have the greatest influence on starch particle volume. The objective of this study was to determine the gene dosage effect upon starch particle volume at the h locus. Two inbreds, B37 and Oh43, were studied in 1992 and 1993, and their hybrid B37 x Oh43 was studied in 1993. Appropriate crosses were made to establish four endosperm genotypes + +/+, + +/h, hh/+ and hh/h. Starch was extracted from mature kernels collected for each endosperm genotype and analysed for particle volume. The source of variation attributable to fitting two straight regression lines on number of h alleles was highly significant (P < 0.01) in all experiments, resulting in a horizontal-line relationship among the three normal genotypes (++/+, ++/h and hh/+) at 14.452 mu m(3) and a regression line of slope 1.622 mu m(3) passing from hh/ + to hh/h. There is no dosage effect of starch particle volume at the h locus; complete recessiveness of the h allele for starch particle volume is the same as the visual phenotypic observation of soft starch.