Multiple resistance to ACCase and ALS-inhibiting herbicides in Beckmannia syzigachne (Steud.) Fernald without mutations in the target enzymes

ABSTRACT American slough grass ( Beckmannia syzigachne (Steud.( Fernald) is a worldwide weed and is widely distributed in rice-wheat rotations in China. Fenoxaprop- P -ethyl and mesosulfuron-methyl are two major herbicides used to control B. syzigachne . Resistance has evolved in B. syzigachne under continuous selective pressure from herbicides. This study aimed to establish the cross-resistance pattern of a resistant population and explore the potential non-target-site based resistance mechanisms of B. syzigachne . Sequencing of target enzyme genes (acetyl coenzyme A carboxylase (ACCase( and acetolactate synthase (ALS() revealed that there were no resistance-endowing amino acid substitutions in the resistant B. syzigachne population (R F1 ) compared with the sensitive population (S F1 ), and obtained the purified materials. Furthermore, piperonyl butoxide (PBO) and malathion showed synergistic effects with fenoxaprop- P -ethyl and mesosulfuron-methyl respectively in R F1 . Therefore, we speculate that the resistance observed in B. syzigachne was related with metabolic, mostly involving the cytochrome P450 enzymes. Cross resistance patterns showed that the purified resistant B. syzigachne produce high resistance to fenoxaprop- P -ethyl and pyroxsulam; intermediate resistance to flucarbazone-sodium; low resistance to quizalofop- P -ethyl, clodinafop-propargyl, sethoxydim and mesosulfuron-methyl; sensitive to clethodim pinoxaden and isoproturon. Key words:  Herbicide resistance; metabolic resistance; P450 inhibitors; target enzymes sequencing.