Target Site–Based Resistance to Penoxsulam in Late Watergrass (Echinochloa phyllopogon) from China

• Published in: Weed science Vol. 67; no. 4; pp. 380 - 388
• Main Authors: Liu, Jian, Fang, Jiapeng, He, Zongzhe, Li, Jun, Dong, Liyao
• Format: Journal Article
• Language: English
• Published: New York, USA The Weed Science Society of America 01.07.2019; Cambridge University Press
• Subjects: Acetolactate synthase; Acetolactate synthase (ALS); Affinity; amino acid mutation; Binding; Bioassays; Bulbostylis barbata; cross-resistance; Echinochloa phyllopogon; Herbicide resistance; Herbicides; Inhibitors; Molecular docking; Mutation; Population studies; Research Article; resistance mechanism; Rice fields; Seeds; Sulfonylurea; Target recognition; United States > US; China; Acetolactate synthase (ALS); cross-resistance; resistance mechanism; amino acid mutation; Patrick Tranel, University of Illinois at Urbana-Champaign
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1017/wsc.2019.14

Late watergrass [Echinochloa phyllopogon (Stapf) Koso-Pol.] is one of the most persistent weeds in rice fields and shows resistance to some acetolactate synthase (ALS)-inhibiting herbicides, such as penoxsulam. Previous studies of E. phyllopogon's herbicide resistance have focused on non–target site resistance mechanisms. In this study, E. phyllopogon populations from Heilong Jiang Province, China, that were possibly resistant to penoxsulam were used to identify the target site–based mechanisms of resistance. Population HSRH-520 showed a 25.4-fold higher resistance to penoxsulam than the sensitive population, HSRH-538. HSRH-520 was resistant to other ALS inhibitors, with resistance indexes ranging from 17.1 to 166. Target-gene sequence analysis revealed two different ALS genes in E. phyllopogon; a Pro-197-Ser substitution occurred in the ALS-2 gene of HSRH-520. In vitro activity assays revealed that the penoxsulam concentrations required to inhibit 50% of the ALS activity were 13.7 times higher in HSRH-520 than in HSRH-538. Molecular-docking tests showed that the Pro-197-Ser mutation reduced the binding affinity between ALS and ALS inhibitors belonging to the triazolopyrimidine, sulfonylaminocarbonyltriazolinone, and sulfonylurea families, and there were almost no effects on binding affinity when the ALS inhibitors were of the pyrimidinylthiobenzoate and imidazolinone families. Overall, the results indicated and verified that the Pro-197-Ser mutation leads to increased ALS activity by reducing the binding affinity of the inhibitor and ALS. This is the first report on the Pro-197-Ser mutation in the complete ALS gene of E. phyllopogon and will aid future research of target site–based resistance mechanisms of E. phyllopogon to ALS inhibitors.