Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Iowa Long Ear Synthetic (BSLE) was developed in 1957 from 12 long-eared maize (Zea mays L.) inbred lines. After three generations of random mating, divergent mass selection for ear length was initiated in 1963 to determine the effects of selection on grain yield. The objectives of this study were to evaluate the effects of 15 cycles of mass selection on ear length, yield, and other agronomic traits and to estimate the genetic variability present in BSLE original population and in subpopulations after 15 cycles of divergent mass selection for ear length;Evaluation of original and advanced cycles of BSLE subpopulations showed significant but asymmetrical response for ear length and most of the other taits. Greater response was exhibited with selection for shorter ears. The asymmetrical response for ear length was probably due to genetic asymmetry and greater environmental sensitivity of long-ear subpopulation compared with the short-ear subpopulation. The effects of genes controlling ear length were also concluded to be small because the asymmetric response was not immediate. Heterosis was detected in the crosses of advanced cycles suggesting significant difference in gene frequencies in the short-ear and long-ear subpopulations with the expression of incomplete dominance for ear length;Genetic variation in the advanced populations, cycle 15 short-ear (BSLE C15S) and cycle 15 long-ear (C15L), was found to be similar to the original population (BSLE C0). Further progress was predicted and would continue to be asymmetrical in future cycles of divergent mass selection for ear length. Indirect selection, based on ear length, was not effective for increasing grain yield. Correlated effects for divergent mass selection were opposite for the short-ear and long-ear subpopulations.



Digital Repository @ Iowa State University,

Copyright Owner

Artemio Manto Salazar



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168 pages