Resistance to clethodim in Italian ryegrass (Lolium perenne ssp. multiflorum) from Mississippi and North Carolina

Abstract

BACKGROUND Clethodim, an acetyl‐CoA carboxylase (ACCase)‐inhibiting herbicide, is one of the few postemergence chemical control options available to growers of Mississippi to manage glyphosate and/or other herbicide resistant Italian ryegrass populations. Recently, clethodim failed to adequately control Italian ryegrass populations across Mississippi. A sethoxydim, also an ACCase inhibitor, ‐resistant Italian ryegrass population from North Carolina was cross‐resistant to clethodim. This research characterized the magnitude and mechanisms of clethodim resistance in the Mississippi and North Carolina Italian ryegrass populations via whole‐plant herbicide dose response, cross resistance, and metabolism studies, and molecular analysis. RESULTS Two clethodim‐resistant biotypes from Mississippi, MS24 and MS37, were 10‐ and 4‐fold resistant, respectively, relative to a susceptible (SUS1) biotype. A North Carolina biotype, NC21, was 40‐fold resistant to clethodim compared to SUS1. Two additional biotypes from North Carolina, NC22 and NC 23, recorded shoot dry weight reduction of only 17–30% of nontreated at the highest clethodim dose of 2.17 kg ha−1, (8×). The NC22 biotype was cross‐resistant to sethoxydim, fluazifop, quizalofop, and pinoxaden. Metabolic inhibitors such as piperonyl butoxide and 4‐chloro‐7‐nitrobenzofurazan did not affect resistance of MS37, MS51, and NC22 biotypes to fenoxaprop, clethodim, or pinoxaden. The MS37 biotype had three target site mutations, I2041N, C2088R, and G2096A. Another clethodim‐resistant biotype from Mississippi, MS51, had only the C2088R substitution. The NC22 and NC23 biotypes had I1781L, I2041N, and D2078G replacements. CONCLUSION This study shows that the mechanism of resistance to clethodim in Italian ryegrass from Mississippi and North Carolina is due to target site modifications in the ACCase gene leading to broad cross‐resistance to other ACCase‐inhibiting herbicides. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

Transfer of resistance alleles from herbicide-resistant to susceptible grass weeds via pollen-mediated gene flow

“…Italian ryegrass populations have evolved resistance to herbicides with at least nine different SOAs (Ghanizadeh et al 2015;Heap 2021), including acetyl CoA carboxylase (ACCase) inhibitors (Bobadilla et al 2021;Bravin et al 2001;Kaundun 2010;Mahmood et al 2016;Nandula et al 2020;Rauch et al 2010;Stranger and Appleby 1989), acetolactate synthase (ALS) inhibitors (Bobadilla et al 2021;Délye et al 2009;Mahmood et al 2016;Rauch et al 2010;Shimono et al 2015), carotenoid biosynthesis inhibitors (Ghanizadeh et al 2015), EPSPS inhibitor (glyphosate; Bobadilla et al 2021;Dickson et al 2011;Jasieniuk et al 2008;Niinomi et al 2013;Perez and Kogan 2003;Perez-Jones et al 2005;Preston et al 2009;Salas et al 2012), glutamine synthase inhibitors (Avila-Garcia et al 2011Fernández et al 2017;Ghanizadeh et al 2015;Karn et al 2018;Kurata et al 2017), protoporphyrinogen oxidase (PPO) inhibitors (Fernández et al 2017), photosystem I inhibitors (Brunharo and Hanson 2018;Tehranchian et al 2018), photosystem II (PS II) inhibitors (Bobadilla et al 2021;Liu et al 2014), and very long chain fatty acid (VLCFA) inhibitors (Bobadilla et al 2021;Liu et al 2014Liu et al , 2016Rauch et al 2010). Resistance to ACCase inhibitors and the EPSPS-inhibiting herbicide glyphosate are the most frequently reported ...…”

Glyphosate-resistant Italian ryegrass (Lolium perenne ssp. multiflorum) control with preemergence and postemergence herbicide programs

“…The first DR Italian ryegrass population was documented in Oregon in 1987 (Betts et al 1992), and 12 U.S. states have documented Italian ryegrass resistance to diclofop since that time (Heap 2021). Herbicides such as glyphosate, imazamox, mesosulfuron, and pinoxaden have been used for postemergence (POST) control of Italian ryegrass in wheat as well as additional economically important row crops throughout the United States (Bond et al 2005;Ellis et al 2008;Jordan et al 2001;Kuk and Burgos 2007); however, resistance to these herbicides has been documented in Mississippi (Bond et al 2014;Bond 2018;Heap 2021;Nandula et al 2019). Therefore, POST herbicides are limited to clethodim and/or paraquat for herbicide-resistant Italian ryegrass control in Mississippi (Bond et al 2005;Bond 2018;Eubank et al 2012).…”

“…Additionally, clethodim was more effective for Italian ryegrass control than other ACCase-inhibiting herbicides, and potential resistance to this herbicide was the rarest among 12 herbicides evaluated (Rauch et al 2010). However, repetitive use of this herbicide has resulted in clethodim-resistant Italian ryegrass biotypes in seven Mississippi counties (Nandula et al 2019). The loss of clethodim in recent years has left some Mississippi producers with paraquat as the only POST herbicide for Italian ryegrass control (Bond 2018;Nandula et al 2019).…”

“…However, repetitive use of this herbicide has resulted in clethodim-resistant Italian ryegrass biotypes in seven Mississippi counties (Nandula et al 2019). The loss of clethodim in recent years has left some Mississippi producers with paraquat as the only POST herbicide for Italian ryegrass control (Bond 2018;Nandula et al 2019).…”

“…During spring preplant burndown applications, Italian ryegrass may be larger in size (30 to 60 cm) and often requires two paraquat applications spaced 10 to 14 d apart (Bond 2018). Therefore, paraquat should be applied when Italian ryegrass plants are small, and roots are not well established (Nandula et al 2019). To date, paraquat-resistant Italian ryegrass has been confirmed only in California in the United States (Heap 2021; Tehranchian et al 2019).…”