Physiological and Molecular Basis of Acetolactate Synthase-Inhibiting Herbicide Resistance in Barnyardgrass (Echinochloa crus-galli)

Abstract

Barnyardgrass biotypes from Arkansas (AR1 and AR2) and Mississippi (MS1) have evolved cross-resistance to imazamox, imazethapyr, and penoxsulam. Additionally, AR1 and MS1 have evolved cross-resistance to bispyribac-sodium. Studies were conducted to determine if resistance to acetolactate synthase (ALS)-inhibiting herbicides in these biotypes is target-site or non-target-site based. Sequencing and analysis of a 1701 base pair ALS coding sequence revealed Ala₁₂₂ to Val and Ala₁₂₂ to Thr substitutions in AR1 and AR2, respectively. The imazamox concentrations required for 50% inhibition of ALS enzyme activity in vitro of AR1 and AR2 were 2.0 and 5.8 times, respectively, greater than the susceptible biotype. Absorption of ¹⁴C-bispyribac-sodium, -imazamox, and -penoxsulam was similar in all biotypes. ¹⁴C-Penoxsulam translocation out of the treated leaf (≤2%) was similar among all biotypes. ¹⁴C-Bispyribac-treated AR1 and MS1 translocated 31- 43% less radioactivity to aboveground tissue below the treated leaf compared to the susceptible biotype. ¹⁴C-Imazamox-treated AR1 plants translocated 39% less radioactivity above the treated leaf and aboveground tissue below the treated leaf, and MS1 translocated 54 and 18% less radioactivity to aboveground tissue above and below the treated leaf, respectively, compared to the susceptible biotype. Phosphorimaging results further corroborated the above results. This study shows that altered target site is a mechanism of resistance to imazamox in AR2 and probably in AR1. Additionally, reduced translocation, which may be a result of metabolism, could contribute to imazamox and bispyribac-sodium resistance in AR1 and MS1.

First report of resistance to acetolactate‐synthase‐inhibiting herbicides in yellow nutsedge (Cyperus esculentus): confirmation and characterization

“…8,16 Samples (3-4 g) of fresh shoot tissue (bulked from 5-8 individual plants) were measured, immediately frozen and ground in liquid nitrogen and stored at −80 ∘ C until further analysis. The herbicide concentrations used were 0, 0.001, 0.01, 0.1, 1, 10, 100 and 1000 M for halosulfuron.…”

“…6,7 Introduction of imidazolinone (IMI)-resistant rice and overreliance on ALS-inhibiting herbicides for several years has led to the evolution of ALS-resistant weeds in midsouthern United States rice. 8 Several reports of ALS-inhibiting herbicide-resistant weeds such as barnyardgrass (Echinochloa crus-galli L.), 9 smallflower umbrella sedge (Cyperus difformis L.) 10 and rice flatsedge (Cyperus iria L.) 11 have been documented in Arkansas rice, which demonstrates considerable adaptive evolution of these weed species to ALS inhibitors. In 2012, a rice grower in Arkansas failed to control yellow nutsedge with halosulfuron.…”

Identification of Herbicide-Resistant Barnyardgrass (Echinochloa crus-galli var. crus-galli) Biotypes in Korea

“…E. oryzicola cross-resistance to ALSherbicides was due to the result of Trp574Leu mutation. Barnyardgrass biotypes from Arkansas (AR1 and AR2) and Mississippi (MS1) have evolved cross-resistance to ALSinhibiting herbicides, imazamox, imazethapyr, penoxsulam and bispyribac-sodium (Riar et al, 2013). The crossresistance between two or more herbicides in an herbicide resistant weed biotype is conferred by a single mechanism.…”

Procedures for Detection of Resistant Weeds Using 14C- Herbicide Absorption, Translocation, and Metabolism

“…Riar et al [8] studied three barnyardgrass (Echinochloa crus-galli) biotypes from the United States with cross-resistance to imazamox, imazethapyr, penoxsulam, and bispyribac-sodium. The authors concluded that reduced translocation could contribute to imazamox and bispyribac-sodium resistance for two out of three biotypes.…”