Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level



Crop, Soil & Environmental Sciences


Nilda Roma-Burgos

Committee Member

Christopher A Saski

Second Committee Member

Jeffrey A Lewis

Third Committee Member

Mary C Savin

Fourth Committee Member

Thomas R Butts


gene amplification;gene overexpression;glufosinate;herbicide resistance;Liberty 280;Palmer amaranth


Palmer amaranth is one of the most troublesome weeds in worldwide agriculture. Among the traits that confers extreme weediness to this species, the ability to adapt to herbicide selection pressure stands out. The latest herbicide to which Palmer amaranth developed resistance is glufosinate-ammonium (GFA), an inhibitor of the enzyme glutamine synthetase (GS). The main objectives of this work were: 1) evaluate the resistance level of a Palmer amaranth population from Missouri, USA, 2) determine the mechanisms conferring GFA resistance in Palmer amaranth, 3) elucidate the behavior of amplified GS copies in GFA-resistant Palmer amaranth in terms of inheritance, stability and physical localization, and 4) evaluate the efficacy of herbicides from different modes of action. Our results indicates that Palmer amaranth achieves overproduction of the chloroplastic GS isoform (GS2) via gene amplification and overexpression. This theory was confirmed through biochemical (ammonia accumulation in Palmer amaranth resistant plants) and physiological (photosynthesis inhibition in transformed Nicotiana benthamiana plants) approaches. GS2 copy number varies within plants, as a result of somatic mosaicism observed at the cellular level. Segregation of GS2 copies does not follow Mendelian patters. GFA resistance in this population can be managed by most of the soil-applied commonly used herbicides, and foliar-applied glyphosate, acetolactate synthase- and protoporphyrinogen oxidase-inhibitors, are ineffective against this Palmer amaranth population. Knowledge generated in this research will serve as a basis for future, deeper investigations.

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