Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Arnel R. Hallauer


Maize (Zea mays L.) ear length is positively correlated with grain yield. Thirty generations of selection for increased ear length, however, failed to increase grain yield in Iowa Long-Ear Synthetic (BSLE). Negative correlations between ear length and other yield-related traits complicated indirect selection for grain yield. The main objective of this investigation was to identify quantitative trait loci (QTL) that affect the variation of ear length, grain yield, and other ear traits, and the correlations among traits. Secondary objectives were to validate QTL by comparing their genetic positions across generations, environments, and other populations. QTL were mapped in the F2 and F2:3 generations of a bi-parental population. The inbred parents differed in ear length by 14 cm, and were derived from the divergent sub-populations of BSLE.;More QTL were detected for ear length (16), kernel-row number (12), and kernel depth (6) than detected in prior QTL studies. Eighty percent of the alleles for increased trait values originated from the parent with the higher trait value. Most QTL were validated by one of three methods. More than 67% of the QTL were identified in at least two F2:3 environments. Forty-three percent of the QTL from the F2:3 mean environment were previously identified in the F2. Seven QTL for ear length, one for kernel-row number, and two for grain yield seemed to coincide with QTL in other populations. Traits with higher heritabilities generally had more coincidental QTL, and traits with lower heritabilities generally had fewer coincidental QTL. QTL positions and the parental origin of alleles agreed with the direction of the genetic correlation coefficients. The magnitude of the correlations was generally explained by the frequency of QTL that coincided or were genetically linked. Repulsion-phase linkage between ear length and grain yield QTL near the centromere of chromosome 5 may have caused the failure of ear length selection in BSLE to increase grain yield. QTL on chromosome 6 exemplified the genetic basis for the positive correlation between ear length and grain yield.



Digital Repository @ Iowa State University,

Copyright Owner

Andrew Jon Ross



Proquest ID


File Format


File Size

126 pages