Glyphosate‐resistant Lolium multiflorum in Chilean orchards

Abstract

Summary Lolium multiflorum (Italian ryegrass) seeds suspected of being resistant to glyphosate were collected from fruit orchards at two locations, San Bernardo (SB) and Olivar (OL), Chile, that had been treated an average of three times per year with the isopropylamine salt of glyphosate during the previous 8–10 years. Laboratory experiments were conducted for each orchard population and a susceptible population, a commercial cultivar called Tama (TM), using Petri dishes containing filter paper saturated with 5 mL of glyphosate solution (0–160 mg a.e. L−1). Pot dose–response experiments were also conducted in the greenhouse. The three L. multiflorum populations were treated with glyphosate (0.00–4.32 kg a.e. ha−1). The dose needed to reduce shoot length (Petri dish experiment) and fresh weight (pot dose–response experiment) by 50% was determined for each population. Compared with the TM population, the Petri dish experiment found that the SB and OL populations were five‐ and sixfold, respectively, more resistant to glyphosate, whereas the pot dose–response experiment found that the SB and OL populations were two‐ and fourfold, respectively, more resistant to glyphosate. These results confirm a new case of glyphosate resistance in a novel species, L. multiflorum, and correspond to the first case of glyphosate resistance reported from South America.