Title

Field measurements and modeling study of atmospheric gene flow from corn crop

Date of Completion

January 2004

Keywords

Agriculture, Agronomy|Environmental Sciences

Degree

Ph.D.

Abstract

A total of four gene flow experiments for genetically modified corn crops were conducted, of which two experiments used male-sterile bait plants, and two used male-fertile bait plants. Dynamic pollen release was affected by plant biological characteristics and weather conditions. The spatial distribution of pollen deposition, and outcrossing ratio with distance from source followed the power law. Using male-sterile bait plants obtained significantly higher gene flow estimation than using male-fertile regular plants (average 17 times difference). ^ A simulation model of dynamic atmospheric pollen dispersion and deposition, and final outcrossing from transgenic corn crop, was developed, validated, and used in assessing gene flow for different source field sizes, source strengths, buffer heights, buffer field sizes, atmospheric conditions, and pollen setting speeds. Dynamic pollen dispersion and deposition were predicted by a 3-D Random-Walk model according to inputs of weather data, plant characteristics, and domain dimensions. Actual gene flow (outcrossing ratio) was obtained according to predicted grand total deposition flux at silk height. The model was validated by experimental data and predicts gene flow with acceptable accuracy (the average normalized gross errors were below 1.5). The simulations provided 1% and 0.1% distances for depositions and estimated outcrossing ratios at the distances for different sizes of transgenic cornfields from one plant area of 0.1 m2 to 3.1 × 106 m2 under normal weather conditions. The simulations of the model have shown that source sizes, source strengths, buffer heights, buffer sizes, atmospheric conditions, and pollen settling speeds had important effects on gene flow. While the atmospheric conditions and pollen settling speeds cannot be controlled, choosing appropriate buffer heights and sizes will effectively prevent gene flow. In addition, effective lost seed control is crucial to limit gene flow. ^