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

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.

Mechanism of Resistance to S-metolachlor in Palmer amaranth

“…Crop selectivity to several chloroacetamide herbicides and safeners is mediated by enhanced GST activity, as a result of increased GST expression (Leavitt and Penner, 1979;Lamoureux and Rusness, 1989;Frova, 2006;Riechers et al, 2010). Enhanced amount of GSTF1 protein, a biomarker of NTST was found in L. rigidum population that showed reduced sensitivity to VLCFA inhibitors Torra et al (2021). Thus far, resistance to VLCFA inhibitors in weedy species is attributed to NTSR mechanism mediated by enhanced GST activity (Busi et al, 2018;Brabham et al, 2019;Dücker et al, 2020).…”

The Basis of Tolerance Mechanism to Metsulfuron-Methyl in Roegneria kamoji (Triticeae: Poaceae)

“…Metsulfuron-methyl is widely known for its low use doses, high efficacy and crop selectivity, and broad-spectrum in controlling many broadleaf and grass weeds [ 29 ]. Resistance to Metsulfuron-methyl has been reported in several monocotyledonous weeds, such as Lolium rigidum [ 21 , 30 ], Avena fatua [ 12 ], and Polypogon fugax [ 31 ]. In this study, the four R, kamoji populations showed no symptoms after being treated with metsulfuron-methyl at recommended field dose.…”

“…To date, at least 29 amino acid substitutions have been identified at eight sites [ 13 , 14 , 15 , 16 , 17 ]. However, the non-target-site resistance (NTSR) mechanism, endowed by the metabolism of ALS inhibitors by key enzymatic complexes such as glutathione S -transferases (GST) and cytochrome P450 monooxygenases (CytP450), was also identified in some weed species [ 18 , 19 , 20 , 21 ].…”

Problems and perspectives in weed management

“…For example, in wheat growing areas in Europe the widespread presence of Acetyl CoA Carboxylase inhibitors (ACCase-inhibitors) resistant grass weeds, such as Lolium spp., has forced farmers to replace the once-predominant herbicides with Acetolactate Synthase inhibitors (ALS-inhibitors). However, after a few years of reliance on these latter herbicides, resistance has evolved also against ALS-inhibitors and weeds with multiple resistance are now common (Loureiro et al, 2017, Torra et al, 2021. Farmers then adopt other classes of herbicides to support or replace those that have reduced efficacy due to the evolution of herbicide resistance, entering in a continuous process of new herbicide use or combining new herbicides that can be referred to as a "herbicide treadmill" following the concept of the "pesticide treadmill" (Foster and Magdoff, 2000).…”