Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Mark E. Westgate


Genetically modified agricultural field crops have provided a new lens with which to view transgenic plant engineering. Production of hybrid corn (Zea mays L) depends on cross-pollination between male and female inbred parents. As such, reproductive isolation of seed fields is required to ensure genetic purity of the hybrid progeny. Customer demand for improved genetic purity prompted the seed industry to examine the level of genetic purity resulting from current isolation practices. This project was a two-pronged approach: (1) A three-year study was conducted to monitor purity of hybrid seed produced in 291 fields from 24 seed companies in North America; and (2) Evaluate a particulate model to determine whether it could be used to run multiple different seed production scenarios involving meteorological, positional and biological data to evaluate these dynamic elements on the production of genetically pure seed maize. Industry practices that most consistently contributed to high levels of genetic purity were (i) use of 'Good' or 'Fair' pollen parents, (ii) isolation greater than 165 ft from all potential adventitious pollen sources, (iii) and large (>100 ac) seed field size. The modeling study produced evidence that models may be especially valuable for evaluating multiple "what if" seed production scenarios involving adventitious pollen movement. However, the ISCST3 model is effective estimating gross extra-field pollen movement, but lacks the precision to quantify absolute extra-field pollen quantities needed to accurately estimate seed field adventitious presence. The learnings from this project advance what the seed maize industry knows regarding seed field isolation practices and provides a solid base for further investigation applying models to assessing risk of adventitious presence within seed production.



Digital Repository @ Iowa State University,

Copyright Owner

Dale Steven Ireland



Proquest ID


File Format


File Size

100 pages