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1 October 2016 Characterization of Fenoxaprop-P-Ethyl–Resistant Junglerice ( Echinochloa colona) from Mississippi
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A population of junglerice from Sunflower County, MS, exhibited resistance to fenoxaprop-P-ethyl. An 11-fold difference in ED50 (the effective dose needed to reduce growth by 50%) values was observed when comparing the resistant population (249 g ae ha−1) with susceptible plants (20 g ae ha−1) collected from a different field. The resistant population was controlled by clethodim and sethoxydim at the field rate. Sequencing of the acetyl coenzyme A carboxylase, which encodes the enzyme targeted by fenoxaprop-P-ethyl, did not reveal the presence of any known resistance-conferring point mutations. An enzyme assay confirmed that the acetyl coenzyme A carboxylase in the resistant population is herbicide sensitive. Further investigations with two cytochrome P450 inhibitors, malathion and piperonyl butoxide, and a glutathione-S-transferase inhibitor, 4-chloro-7-nitrobenzofurazan, did not indicate involvement of any metabolic enzymes inhibited by these compounds. The absence of a known target-site point mutation and the sensitivity of the ACCase enzyme to herbicide show that fenoxaprop-P-ethyl resistance in this population is due to a non–target-site mechanism or mechanisms.

Nomenclature: Clethodim; fenoxaprop-P-ethyl; sethoxydim; junglerice, Echinochloa colona Link. ECHCO

Alice A. Wright, Vijay K. Nandula, Logan Grier, Kurt C. Showmaker, Jason A. Bond, Daniel G. Peterson, Jeffery D. Ray, and David R. Shaw "Characterization of Fenoxaprop-P-Ethyl–Resistant Junglerice ( Echinochloa colona) from Mississippi," Weed Science 64(4), 588-595, (1 October 2016).
Received: 13 February 2016; Accepted: 1 June 2016; Published: 1 October 2016

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