Degree Type

Dissertation

Date of Award

1994

Degree Name

Doctor of Philosophy

Department

Agronomy

First Advisor

Linda Pollack

Second Advisor

Pamela White

Abstract

Differential scanning calorimetry (DSC) was used to identify genotypic and environmental effects on maize starch properties. Significant (P ≤ 0.01) differences were observed among three genotypes (OH43, A632 and OH43xA632) for gelatinization onset (T[subscript] o), peak (T[subscript] p), and enthalpy ([delta]H). Later planting dates for these genotypes also resulted in greater values for T[subscript] p, [delta]H and range. Upon examination of 25 maize inbreds grown in two years, significant (P ≤ 0.01) difference were seen for all DSC values. A significant inbred x year effect was observed for all DSC values with the exception of [delta]H. Six inbreds were selected on the basis of having the highest and lowest T[subscript] p, [delta]H and range in order to evaluate functional properties of the starches. Several significant (P ≤ 0.05) correlations were seen between DSC values and starch paste viscosities and gel strengths. Results from these studies indicate that the DSC can be used to predict starch functional properties among nonmutant maize genotypes;A complete sugary-2 (su[subscript]2) dosage series was produced in an OH43 maize inbred background. A study was conducted to determine if an effect of gene dosage exists at the su[subscript]2 locus for starch characteristics other than amylose content. Amylose content was determined from these samples using colorimetric and amperometric titration methods. No effect of gene dosage at the su[subscript]2 locus was observed, which was in agreement with previous finding. Starch thermal properties measured by DSC revealed a dosage effect for T[subscript] o, T[subscript] p, [delta]H, range and the percent retrogradation. X-ray diffraction patterns also suggested a dosage effect for relative crystallinity values. Viscosities of starch pastes and gel strengths resulting from genotypes possessing one or two doses of the su[subscript]2 allele exceeded values observed for mutant and normal genotypes. The presence of genetic modifying genes from exotic maize germplasm on thermal properties of su[subscript]2 genotypes was also examined. Populations containing 50% exotic germplasm were found to have larger ranges for several DSC parameters. In addition, several DSC values from starches of these populations were significantly (P < 0.05) different from those of the inbred OH43su[subscript]2 which was used as a control. The results from this study indicate that the DSC may be a useful method for rapidly identifying unique starch properties not detectable by considering amylose content alone. Selection on the basis of DSC values may lead to desired starch properties.

DOI

https://doi.org/10.31274/rtd-180813-11588

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Mark Robert Campbell

Language

en

Proquest ID

AAI9503535

File Format

application/pdf

File Size

172 pages

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