Distribution, frequency and molecular basis of penoxsulam, metamifop and florpyrauxifen-benzyl resistance in Echinocloa spp. from rice fields across Jiangsu Province, China

Abstract

Barnyard grasses (Echinochloa spp.) are the most troublesome weeds in rice ecosystems of Jiangsu Province, China, and long-term use of herbicides inevitably cause the development of resistance. In this study, 122 field-sampled populations were tested for resistance to penoxsulam (PEN), metamifop (MET), florpyrauxifen-benzyl, (FPB), propanil, and tripyrasulfone. Field-dose assays revealed that 51, 7, and 6 populations have either developed or were developing resistance to penoxsulam, metamifop and florpyrauxifen-benzyl, and all 122 populations were still sensitive to propanil and tripyrasulfone. Dose-response assays identified that 41.8 % of populations exhibited 6- to 830-fold resistance to PEN; 5.7 % of populations displayed 2.2- to 13.9-fold resistance to MET; and 4.9 % of populations showed 2.4- to 11.1-fold resistance to FPB. Trp-574-Leu mutations in EcALS1 or EcALS3 were found in 18.0 % of populations. Trp-2027-Cys, Cys-2088-Arg, and Gly-2096-Ala mutations in EcACC1, EcACC3, or EcACC5 were detected in 4.1 % of populations, and no known resistance-associated target-site gene mutations were confirmed in the rest of herbicide-resistant populations. Furthermore, the P450 inhibitor malathion and GST inhibitor NBD-Cl significantly reduced the resistance to three herbicides in 38.5 % of populations, especially those without the target-site gene mutations, indicating both target-site mutations and P450s and/or GSTs-mediated metabolisms play important roles in herbicide resistance evolution in Echinochloa spp. These findings are helpful to formulate an appropriate strategy for effective and sustainable control of Echinochloa spp. by mixtures of herbicide with different modes of action and mitigate weed resistance evolution.