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Grantee Research Project Results

NCER Grantee Research Project Results

Evaluating the Effects of Genetically Modified Plants on Symbiotic Fungi in the Soil Ecosystem

EPA Grant Number: FP917125
Title: Evaluating the Effects of Genetically Modified Plants on Symbiotic Fungi in the Soil Ecosystem
Investigators: Cheeke-Icoz, Tanya E.A.
Institution: Portland State University
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: September 1, 2010 through August 31, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010)
Research Category: Academic Fellowships , Fellowship - Ecosystem Services: Terrestrial Systems Soil and Plant Ecology



Genetically modified corn has been grown commercially since 1996 and now constitutes 80% of all corn grown in the United States, yet the ecological effects of this technology in the soil ecosystem have not been thoroughly evaluated. My dissertation research aims to develop an understanding of the mechanisms that both enable and limit arbuscular mycorrhizal fungal (AMF) colonization in transgenic plants with the overall goal of determining whether Bt crop cultivation has an inhibitory effect on AMF abundance and diversity in the soil ecosystem. Some of my primary objectives are to: 1) identify key mechanisms for AMF establishment in the Bt model system by examining fundamental differences in root permeability, root exudates, and Bt toxin accumulation in the root zone among multiple Bt and non-Bt maize isolines and 2) to determine the impact of Bt maize on the abundance and diversity of AMF in the roots and rhizosphere under field conditions.


Currently, 80% of the corn grown in the US is genetically modified yet the ecological effects of this technology on soil organisms have not been thoroughly evaluated. Healthy plant-microbe interactions can stimulate plant growth and help protect plants from drought and disease. This research examines whether symbiotic plant-fungal relationships are reduced in transgenic Bt (Bacillus thuringiensis) corn and assesses the effects of Bt crops on the abundance and diversity of arbuscular mycorrhizal fungi in the soil ecosystem.


Microscopic, morphological, and molecular sequencing methods will be used to investigate the effects of transgenic Bt plants on the colonization ability, abundance, and diversity of symbiotic arbuscular mycorrhizal fungi using laboratory, greenhouse, and field studies. Greenhouse and laboratory experiments will be used to investigate possible correlations between the level of AMF colonization in each root system to potential differences in root permeability, root exudate profiles, and/or Bt toxin accumulation in the rhizosphere. Field trials will be performed using Bt isolines engineered to express single or stacked combinations of Cry1Ab, Cry34/35Ab1, Cry3Bb1, and Cry1F Bt proteins (along with the non-transgenic parental controls) to determine the effects of transgenic Bt maize cultivation on symbiotic fungi in the soil ecosystem over multiple growing seasons.

Expected Results:

Results from these experiments will provide a comprehensive assessment of the impact of Bt plants on symbiotic soil fungi across a broad range of environmental and ecological conditions and will investigate possible mechanisms that may influence AMF colonization in Bt maize. The effects of AMF colonization levels on plant growth will be tested by entering AMF census data for each plant as a covariate in the repeated measures and univariate models. Depending on the extent to which Bt toxin levels and other compounds in the root exudate profiles vary independently among modified isolines, we will be able to assess statistical associations between the concentration of individual compounds and AMF colonization using multiple regression techniques. The identification of groups of compounds that are associated with lower fungal colonization will lead to the development of new hypotheses and experiments aimed at identifying causal mechanisms of reduced mycorrhizal associations in Bt-modified plants. Upon completion, this research will contribute to the development of future biotech risk assessment protocols to minimize the non-target effects of Bt crops on symbiotic fungi and will expand the area of knowledge surrounding these crops.

Potential to Further Environmental/Human Health Protection:

My research will evaluate both the benefits and potential impacts of agricultural biotechnology on the soil environment with the goal of finding an acceptable balance between the use of genetically engineered crops and the preservation of a healthy soil ecosystem.

Supplemental Keywords:

mycorrhizae, biotech, corn, maize, Bt, soil, arbuscular mycorrhizal fungi, transgenic,

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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