Multiple mechanisms jointly promoted the infestation of pinoxaden-resistant Beckmannia syzigachne: a case study with 236 populations

Beckmannia syzigachne (Steud.) Fernald is the most troublesome wheat weed species in eastern China. Pinoxaden, an acetyl-CoA carboxylase (ACCase)-inhibiting herbicide, is one of the most important wheat herbicides against grass weeds including B. syzigachne . Here, we tested 236 B. syzigachne populations for resistance to pinoxaden collected from wheat fields in eastern China. Whole-plant bioassays suggested that 97.0% of the populations were pinoxaden-resistant, with 57.6% exhibiting high to very high resistance, while 11.9% showed pinoxaden-induced hormesis. Among the 85 populations for which the ACCase gene was sequenced, seven amino acid substitutions were detected at six sites, including I1781L (57.6% of populations), D2078G (40.0%), I2041N (35.3%), G2096A (5.9%), W2027C (2.4%), W1999C (1.2%), and W2027L (1.2%). In total, 72 of the 84 resistant populations tested (85.7%) were found to carry target-site mutation(s). Of these populations 48.6%, 23.6%, 19.4% and 8.3% carried one, two, three and four mutation types within a single population, respectively. Metabolic resistance associated with cytochrome P450 monooxygenases (P450) and glutathione S-transferases (GST) was detected in 61.9% and 46.4% of the resistant populations, respectively. Genetic differentiation was detected among populations, with an F ST value of 0.20 ( P < 0.05). Geographical distance was not significantly correlated with genetic differentiation. Together, our results suggest that multiple mechanisms jointly promoted the widespread occurrence of pinoxaden resistance in B. syzigachne .