Target-site and metabolic mechanisms of tolerance to penoxsulam in pond lovegrass (Eragrostis japonica)

Abstract

The identification of herbicide tolerance is essential for effective chemical weed control. According to whole-plant dose-response assays, none of 29 pond lovegrass [Eragrostis japonica (Thunb.) Trin.] populations were sensitive to penoxsulam. The effective dose values of penoxsulam to E. japonica populations causing 50% inhibition of fresh weight (GR50: 105.14 to 148.78 g ai ha-1) were much higher than the recommended dose of penoxsulam (15 to 30 g ai ha-1) in the field. This confirmed that E. japonica was tolerant to penoxsulam. Eragrostis japonica populations showed 52.83- to 74.76-fold higher tolerance to penoxsulam than the susceptible barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.]. The mechanisms of tolerance to penoxsulam in E. japonica were continued to be identified. In vitro activity assays revealed that the penoxsulam concentration required to inhibit 50% of the acetolactate synthase (ALS) activity (IC50) was 12.27-fold higher in E. japonica than that in E. crus-galli. However, differences in the ALS gene, previously found to endow target-site resistance in weeds, were not detected in the sequences obtained. Additionally, the expression level of genes encoding ALS in E. japonica was approximately 2-fold higher than that in E. crus-galli after penoxsulam treatment. Furthermore, penoxsulam tolerance can be significantly reversed by three cytochrome P450 monooxygenases (Cyt P450s) inhibitors (1-aminobenzotriazole, piperonyl butoxide, and malathion) and the activity of NADPH-dependent cytochrome P450 reductase toward penoxsulam in E. japonica increased significantly (approximately 7-fold higher) compared to that of treated E. crus-galli. Taken together, these results indicate that lower ALS sensitivity, relatively higher ALS expression levels, and stronger metabolism of Cyt P450s combined to bring about penoxsulam tolerance in E. japonica.

Research progress of triazole derivatives in the discovery of agricultural chemicals

“…By controlling the activity of ALS in weeds, it destroys the normal physiological metabolism of weeds and causes weed death [34]. while florasulam [35], penoxsulam [36], pyroxsulam [37], diclosulam [38], and cloransulam [39] are triazopyrimidine sulfonamide herbicides. Triazopyrimidine compounds have become a research hotspot in the discovery of new ALS preparations.…”