Abstract
Different Lolium species, common weeds in cereal fields and fruit orchards in Chile, were reported showing isolated resistance to the acetyl CoA carboxylase (ACCase), acetolactate synthase (ALS) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibiting herbicides in the late 1990s. The first case of multiple resistance to these herbicides was Lolium multiflorum found in spring barley in 2007. We hypothesized that other Lolium species may have evolved multiple resistance. In this study, we characterized the multiple resistance to glyphosate, diclofop-methyl and iodosulfuron-methyl-sodium in Lolium rigidum, Lolium perenne and Lolium multiflorum resistant (R) populations from Chile collected in cereal fields. Lolium spp. populations were confirmed by AFLP analysis to be L. rigidum, L. perenne and L. multiflorum. Dose-response assays confirmed multiple resistance to glyphosate, diclofop-methyl and iodosulfuron methyl-sodium in the three species. Enzyme activity assays (ACCase, ALS and EPSPS) suggested that the multiple resistance of the three Lolium spp. was caused by target site mechanisms, except the resistance to iodosulfuron in the R L. perenne population. The target site genes sequencing revealed that the R L. multiflorum population presented the Pro-106-Ser/Ala (EPSPS), Ile-2041-Asn++Asp-2078-Gly (ACCase), and Trp-574-Leu (ALS) mutations; and the R L. rigidum population had the Pro-106-Ser (EPSPS), Ile-1781-Leu+Asp-2078-Gly (ACCase) and Pro-197-Ser/Gln+Trp-574-Leu (ALS) mutations. Alternatively, the R L. perenne population showed only the Asp-2078-Gly (ACCase) mutation, while glyphosate resistance could be due to EPSPS gene amplification (no mutations but high basal enzyme activity), whereas iodosulfuron resistance presumably could involve non-target site resistance (NTSR) mechanisms. These results support that the accumulation of target site mutations confers multiple resistance to the ACCase, ALS and EPSPS inhibitors in L. multiflorum and L. rigidum from Chile, while in L. perenne, both target and NTSR could be present. Multiple resistance to three herbicide groups in three different species of the genus Lolium in South America represents a significant management challenge.
Highlights
Lolium grasses are problematic weeds around the world (Salas et al, 2012; Menegat et al, 2016), causing yield losses in small grains, orchards, and vineyards, as well as in non-agricultural lands (Travlos et al, 2018)
The Asp-376-Glu and Trp-574-Leu mutations conferred resistance to acetolactate synthase (ALS) inhibitors in L. perenne (Menegat et al, 2016); we found no evidence of their participation in the iodosulfuron resistance of the R L. perenne population, which was confirmed by means of the dose-response assays, i.e., target-site resistance (TSR) mechanisms were not involved in such resistance in this species
An accumulation of target site mutations that confer resistance to ALS, ACCase and EPSPS inhibiting herbicides was found in R populations of L. rigidum and L. multiflorum collected in barley and wheat fields in Chile
Summary
Lolium grasses are problematic weeds around the world (Salas et al, 2012; Menegat et al, 2016), causing yield losses in small grains, orchards, and vineyards, as well as in non-agricultural lands (Travlos et al, 2018). There are 17 Lolium species described, but the most problematic ones in agricultural producing systems are L. multiflorum (Lam.) Husnot (Italian ryegrass), L. perenne L. The last species is considered the most economically important weed in Australia, while L. multiflorum and L. perenne are frequents weeds in crops of North and South America and the Mediterranean region (Heap, 2020). There are currently 67, 9, and 48 cases of herbicide resistance in L. multiflorum, L. perenne, and L. rigidum, respectively, recorded in the database of the International Survey of Herbicide Resistant Weeds. At least half of these are cases of cross and/or multiple resistance (Heap, 2020)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
