Physiological, Biochemical and Molecular Characterization of Multiple Herbicide Resistance in Palmer Amaranth (Amaranthus Palmeri)
PHYSIOLOGICAL, BIOCHEMICAL AND MOLECULAR CHARACTERIZATION OF MULTIPLE HERBICIDE RESISTANCE IN PALMER AMARANTH (AMARANTHUS PALMERI) by SRIDEVI NAKKA M.S., Acharya N.G. Ranaga Agricultural University, 2005 M.S., University of Illinois, 2008 AN ABSTRACT OF A DISSERTATION submitted in partial fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Department of Agronomy College of Agriculture KANSAS STATE UNIVERSITY Manhattan, Kansas 2016 Abstract Palmer amaranth (Amaranthus palmeri) is one of the most aggressive, troublesome and damaging broadleaf weeds in many cropping systems including corn, soybean, cotton, and grain sorghum causing huge yield losses across the USA. As a result of extensive and intensive selection of pre- and -post emergence herbicides, Palmer amaranth has evolved resistance to multiple herbicide modes of action, microtubule-, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS)-, acetolactate synthase (ALS)-, photosystem II (PS II)-, hydroxyphenylpyruvate dioxygenase (HPPD)- and more recently to protoporphyrinogen oxidase (PPO)-inhibitors. A Palmer amaranth population from Kansas was found resistant to HPPD-, PS II-, and ALS- inhibitors. The overall objective of this research was to investigate the target-site and/or non- target-site resistance mechanisms in Palmer amaranth from KS (KSR) to mesotrione (HPPD- inhibitor), atrazine (PS II-inhibitor), and chlorsulfuron (ALS-inhibitor) relative to known susceptible Palmer amaranth from Mississippi (MSS) and KS (KSS). Whole plant dose-response assays showed high level of resistance in KSR to mesotrione, atrazine and chlorsulfuron. KSR was 10-18, 178-237 and >275 fold more resistant to mesotrione, atrazine, and chlorsulfuron, respectively, compared to MSS and KSS. Metabolism studies using [14C] labeled mesotrione and atrazine demonstrated non-target-site resistance to both herbicides, particularly, enhanced metabolism of [14C] mesotrione likely mediated by cytochrome P450 monooxygenases and rapid degradation of [14C] atrazine by glutathione S-transferases (GSTs).
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