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17 November 2022 Target-Site and Metabolic Mechanisms of Tolerance to Penoxsulam in Pond Lovegrass (Eragrostis japonica)
Ying Liu, Hao Wang, Jiapeng Fang, Haitao Gao, Jinyi Chen, Zhen Peng, Liyao Dong
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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 causing 50% inhibition of fresh weight (GR50: 105.14 to 148.78 g ai ha–1) in E. japonica populations were much higher than the label rate 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 susceptible barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.]. The mechanisms of tolerance to penoxsulam in E. japonica were also 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 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 in E. crus-galli after penoxsulam treatment. Furthermore, penoxsulam tolerance can be significantly reversed by three cytochrome P450 monooxygenase (CytP450) 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 with that of treated E. crus-galli. Taken together, these results indicate that lower ALS sensitivity, relatively higher ALS expression levels, and stronger metabolism of CytP450s combined to bring about penoxsulam tolerance in E. japonica.

Ying Liu, Hao Wang, Jiapeng Fang, Haitao Gao, Jinyi Chen, Zhen Peng, and Liyao Dong "Target-Site and Metabolic Mechanisms of Tolerance to Penoxsulam in Pond Lovegrass (Eragrostis japonica)," Weed Science 71(1), 29-38, (17 November 2022). https://doi.org/10.1017/wsc.2022.63
Received: 21 May 2022; Accepted: 2 November 2022; Published: 17 November 2022
KEYWORDS
ALS
CytP450s
herbicide tolerance
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