Degree Type


Date of Award


Degree Name

Doctor of Philosophy




The general objective of this study was to determine the potential for selection of maize (Zea mays L.) genotypes that produce grain resistant to physical injury. The materials evaluated were S1 and S2 lines derived from BS17 and BS1(HS)C1 and S2 lines derived from BS1(HS)C1 in hybrid combinations with B73 and MO17. Eight plant and grain traits (kernel shear strength, visual endosperm rating, date of anthesis, harvest moisture, grain breakage, 300-kernel weight, 300-kernel volume, and kernel density) were evaluated for the S1 and S2 lines from BS17 and BS1(HS)C1. Also, five plant and grain traits (root lodging, stalk lodging, grain breakage, harvest moisture, and grain yield) of BS1(HS)C1 S2 lines and S2 line testcross hybrids were evaluated. All materials were grown at two locations, one year for each generation (visual endosperm rating and date of anthesis were evaluated only at Ames);Statistical analyses revealed significant genetic variability in BS17 and BS1(HS)C1 for all traits. Estimated genotype-by-environment variance components for physical grain quality traits were 0 to 66% as large as the estimated genotypic variance components. Heritability estimates (entry mean basis) for grain breakage ranged from 0.48 to 0.67. Nonadditive gene action for grain breakage was indicated by a highly significant S2 line-by-tester interaction. Because the means of S2 lines and S2 line testcross hybrids for grain breakage were similar in magnitude, the presence of nonadditive gene action may be the consequence of bi-directional dominance;The optimum harvest moisture range for physical grain quality preservation was 19 to 26%. Increasing deviations from this optimum range resulted in increasing grain breakage. Grain resistant to breakage tended to be smaller, denser, and higher in shear strength. Correlations of the same traits between generations indicated that S1 and S2 line means would have predictive value for S2 line and S2 line testcross hybrid means, respectively. The data indicated that selection of S1 lines with breakage-resistant grain would result in earlier flowering S2 lines with smaller kernels. A small, positive correlation between S2 line grain breakage and S2 line testcross hybrid yield revealed that selection of S2 lines with superior physical grain quality could result in lower yielding S2 line testcross hybrids.



Digital Repository @ Iowa State University,

Copyright Owner

Duane Ray LeFord



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202 pages