Target-Site and Non-target-Site Resistance Mechanisms Confer Multiple and Cross- Resistance to ALS and ACCase Inhibiting Herbicides in Lolium rigidum From Spain.

Joel Torra,Robert Edwards,José María Montull,Andreu Taberner,Nawaporn Onkokesung,Neil Boonham

doi:10.3389/fpls.2021.625138

Joel Torra, Robert Edwards + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2021.625138

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Abstract

Lolium rigidum is one the worst herbicide resistant (HR) weeds worldwide due to its proneness to evolve multiple and cross resistance to several sites of action (SoA). In winter cereals crops in Spain, resistance to acetolactate synthase (ALS)- and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides has become widespread, with farmers having to rely on pre-emergence herbicides over the last two decades to maintain weed control. Recently, lack of control with very long-chain fatty acid synthesis (VLCFAS)-inhibiting herbicides has been reported in HR populations that are difficult to manage by chemical means. In this study, three Spanish populations of L. rigidum from winter cereals were confirmed as being resistant to ALS- and ACCase-inhibiting herbicides, with broad-ranging resistance toward the different chemistries tested. In addition, reduced sensitivity to photosystem II-, VLCFAS-, and phytoene desaturase-inhibiting herbicides were confirmed across the three populations. Resistance to ACCase-inhibiting herbicides was associated with point mutations in positions Trp-2027 and Asp-2078 of the enzyme conferring target site resistance (TSR), while none were detected in the ALS enzyme. Additionally, HR populations contained enhanced amounts of an ortholog of the glutathione transferase phi (F) class 1 (GSTF1) protein, a functional biomarker of non-target-site resistance (NTSR), as confirmed by enzyme-linked immunosorbent assays. Further evidence of NTSR was obtained in dose-response experiments with prosulfocarb applied post-emergence, following pre-treatment with the cytochrome P450 monooxygenase inhibitor malathion, which partially reversed resistance. This study confirms the evolution of multiple and cross resistance to ALS- and ACCase inhibiting herbicides in L. rigidum from Spain by mechanisms consistent with the presence of both TSR and NTSR. Moreover, the results suggest that NTSR, probably by means of enhanced metabolism involving more than one detoxifying enzyme family, confers cross resistance to other SoA. The study further demonstrates the urgent need to monitor and prevent the further evolution of herbicide resistance in L. rigidum in Mediterranean areas.

Highlights

Lolium rigidum (Gaud.) is a genetically diverse, crosspollinating and globally distributed weed species, that has evolved resistance to herbicides acting on many sites of action (SoA) around the world (Yu and Powles, 2014)
In rainfed cereals from Spain, the first case of a herbicide resistant (HR) L. rigidum Gaud. population was reported in the north-eastern region, with resistance reported to chlortoluron (PSII inhibiting herbicide) and diclofop-methyl (ACCase inhibiting herbicide) in 1995 (Taberner et al, 1995)
All three L. rigidum populations used in this study were poorly controlled by both acetyl CoA carboxylase (ACCase)- and acetolactate synthase (ALS)-inhibiting herbicides

Summary

Introduction

Lolium rigidum (Gaud.) is a genetically diverse, crosspollinating and globally distributed weed species, that has evolved resistance to herbicides acting on many sites of action (SoA) around the world (Yu and Powles, 2014). In Europe, resistance to acetyl CoA carboxylase (ACCase), acetolactate synthase (ALS), 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), glutamine synthase, and protoporphyrinogen oxidase (PPO) inhibiting herbicides has been reported in L. rigidum associated with winter cereals, vineyards and orchards in the southern part of the continent (De Prado et al, 2005; Cirujeda and Taberner, 2010; Kaloumenos et al, 2012; Atanackovic et al, 2015; Fernandez-Moreno et al, 2017; Fernández-Moreno et al, 2017; Heap, 2020). ACCase, ALS, and PSII inhibitors resistance is widespread throughout the Spanish winter cereal cropping system (Loureiro et al, 2017), with 75% of L. rigidum populations in Catalonia exhibiting HR to these SoA (Loureiro et al, 2010, 2017). The resistance problem is becoming even more complex, with HR reported toward other graminicides used in canola, including clethodim and fluazifop-butyl (Cirujeda and Taberner, 2003)

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