Diversified Resistance Mechanisms in Multi-Resistant Lolium spp. in Three European Countries

Abstract

Annual ryegrass species (Lolium spp.) infest cereal crops worldwide. Ryegrass populations with multiple resistance to the acetyl coenzyme A carboxylase (ACCase) and acetolactate synthase (ALS) inhibitors are an increasing problem in several European countries. We investigated the resistance pattern and level of resistance in ryegrass populations collected in Denmark, Greece and Italy and studied the diversity of mechanisms endowing resistance, both target-site and metabolism based. All populations showed high resistance indexes (RI) to the ALS inhibitors, iodosufuron-methyl-sodium + mesosulfuron-methyl (RI from 8 to 70), whereas the responses to the two ACCase inhibitors, clodinafop-propargyl and pinoxaden, differed. The Greek and Italian populations were moderately to highly resistant to clodinafop (RI > 8) and showed low to moderate resistance to pinoxaden (RI ranged from 3 to 13) except for one Italian population. In contrast, the Danish Lolium populations showed low to moderate resistance to clodinafop (RI ranged from 2 to 7) and only one population was resistant to pinoxaden. Different mutant ACCase alleles (Leu1781, Cys2027, Asn2041, Val2041, Gly2078, Arg2088, Ala2096) and ALS alleles (Gly122, Ala197, Gln197, Leu197, Ser197, Thr197, Val205, Asn376, Glu376, Leu574) endowing resistance were detected in the Greek and Italian populations. In several plants, no mutated ALS and ACCase alleles were found showing a great heterogeneity within and among the Greek and Italian populations. Conversely, no mutant ACCase alleles were identified in the four Danish populations and only one mutant ALS allele (Leu574) was detected in two Danish populations. The expression level of nitronate monooxygenase (NMO), glutathione S-transferase (GST) and cytochrome P450s (CYP72A1 and CYP72A2) varied broadly among populations and individual plants within the populations. Constitutive up-regulation of GST, CYP72A1 and CYP72A2 was detected in resistant plants respect to susceptible plants in one Danish and one Italian population. It appears that the mechanisms underlying resistance are rather complex and diversified among Lolium spp. populations from the three countries, coevolution of both target-site resistance and metabolic based herbicide resistance appears to be a common feature in Denmark and Italy. This must be considered and carefully evaluated in adopting resistance management strategies to control Lolium spp. in cereal crops.

Impact of a Novel W2027L Mutation and Non-Target Site Resistance on Acetyl-CoA Carboxylase-Inhibiting Herbicides in a French Lolium multiflorum Population

“…The I1781L mutation was first identified in a Setaria viridis population in 2000 [39]. It was subsequently found in Lolium spp., A. myosuroides, A. fatua, Phalaris minor, Leptochloa chinienis, and Echinochloa crus-galli populations that have evolved resistance to ACCase-inhibiting herbicides [40][41][42][43][44][45]. The I1781L is not affected by a fitness penalty, explaining why the mutation is widely encountered in resistant grass weed populations [36,46].…”

“…It is noteworthy that a cysteine variant at ACCase codon 2027 was also implicated in resistance to ACCase herbicides in several grass weed species, including Lolium spp., A. myosuroides, A. fatua, and L. chinenis to name but a few [41,42,50,51]. As with the leucine allele, the non-conserved cysteine substitution conferred high levels of resistance to FOPs whilst DIM and DEN herbicides were impacted slightly based on yeast-gene replacement assays [22].…”

Impact of a Novel W2027L Mutation And Non-Target Site Resistance On Acetyl-CoA Carboxylase Herbicides In a French Lolium Multiflorum Population

“…A similar observation was made for single Australian and European Lolium spp. populations which contained several target-site resistant mutations and NTSR following extensive selection with ACCase-inhibiting herbicides [38,41]. The insight gained from this study will not only be useful for effectively managing the Lolium multi orum population with alternative herbicidal and non-herbicidal strategies but will also be valuable for designing the next generation of herbicides that can overcome the types of resistance contained in the population.…”

“…[39]. It was subsequently found in Lolium spp., Alopecurus myosuroides, Avena fatua, Phalaris minor, Leptochloa chinienis and Echinochloa crus-galli populations that have evolved resistance to ACCase-inhibiting herbicides [40][41][42][43][44][45]. The I1781L is not affected by a tness penalty explaining why the mutation is widely encountered in resistant grass weed populations [36,46].…”

“…It is noteworthy that a cysteine variant at ACCase codon 2027 was also implicated in resistance to ACCase herbicides in severeal grass weed species, including Lolium spp., Alopecurus myosuroides, Avena fatua, Leptochloa chinenis to name but a few [41,42,50,51]. As with the leucine allele, the non-conserved cysteine substitution conferred high levels of resistance to FOPs whilst DIM and DEN herbicides were impacted slightly based on yeast-gene replacement assays [22].…”