Date of Graduation

5-2023

Document Type

Dissertation

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Roma-Burgos, Nilda

Committee Member

Saski, Christopher A.

Second Committee Member

Lewis, Jeffrey A.

Third Committee Member

Savin, Mary C.

Fourth Committee Member

Butts, Thomas R.

Keywords

Gene amplification; Gene overexpression; Glufosinate; Herbicide resistance; Liberty 280; Palmer amaranth

Abstract

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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