Target-Site and Metabolic Resistance Mechanisms to Penoxsulam in Late Watergrass (Echinochloa phyllopogon) in China

Echinochloa phyllopogon, a malignant weed in Northeast China's paddy fields, is currently presenting escalating resistance concerns. Our study centered on the HJHL-715 E. phyllopogon population, which showed heightened resistance to penoxsulam, through a whole-plant bioassay. Pretreatment with a P450 inhibitor malathion significantly increased penoxsulam sensitivity in resistant plants. In order to determine the resistance mechanism of the resistant population, we purified the resistant population from individual plants and isolated target-site resistance (TSR) and nontarget-site resistance (NTSR) materials. Pro-197-Thr and Trp-574-Leu mutations in acetolactate synthase (ALS) 1 and ALS2 of the resistant population drove reduced sensitivity of penoxsulam to the target-site ALS, the primary resistance mechanisms. To fully understand the NTSR mechanism, NTSR materials were investigated by using RNA-sequencing (RNA-seq) combined with a reference genome. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis further supported the enhanced penoxsulam metabolism in NTSR materials. Gene expression data and quantitative reverse transcription polymerase chain reaction (qRT-PCR) validation confirmed 29 overexpressed genes under penoxsulam treatment, with 16 genes concurrently upregulated with quinclorac and metamifop treatment. Overall, our study confirmed coexisting TSR and NTSR mechanisms in E. phyllopogon's resistance to ALS inhibitors.