Non–target site based resistance to the ALS-inhibiting herbicide mesosulfuron-methyl in American sloughgrass (Beckmannia syzigachne)

Abstract

American sloughgrass [Beckmannia syzigachne (Steud.) Fernald] is one of the most predominant and troublesome weeds in wheat (Triticum aestivum L.) fields rotated with rice (Oryza sativa L.) in China. Mesosulfuron-methyl is one of the main herbicides used to selectively control B. syzigachne in winter wheat fields in China. After many years of application, mesosulfuron-methyl failed to control B. syzigachne in Yutai County. The objectives of this study were to determine the resistance level to mesosulfuron-methyl and other acetolactate synthase (ALS) inhibitors in the B. syzigachne population collected from Yutai County (R) and identify the mechanism of resistance. The results indicated that the R population was 4.1-fold resistant to mesosulfuron-methyl and was cross-resistant to pyroxsulam (600-fold), imazethapyr (4.1-fold), flucarbazone (12-fold), and bispyribac-sodium (12-fold). In vitro assays revealed that ALS in the R population was as sensitive as that in a susceptible (S) population. Gene sequence analysis identified no known resistant mutations in the ALS gene of the R population. Furthermore, real-time quantitative reverse transcriptase PCR experiments indicated that the expression level of the ALS gene in the R population was not different from that of the S population. However, the cytochrome P450 inhibitor malathion reversed the R population's resistance to mesosulfuron-methyl. The result of ultraperformance liquid chromatography–tandem mass spectrometry (UPLC-MS-MS) spectral analysis indicated that the metabolic rates of mesosulfuron-methyl in the R population were significantly faster than in the S population. Therefore, non-target resistance to mesosulfuron-methyl has been demonstrated in the R population. The resistance was very likely caused by enhanced herbicide metabolism.

Pro-197-Ser Mutation in ALS and High-Level GST Activities: Multiple Resistance to ALS and ACCase Inhibitors in Beckmannia syzigachne

“…Cross-resistance is a common phenomenon in weed species resistant to ALS and ACCase inhibitor herbicides, such as Conyza canadensis ( Zheng et al, 2011 ), Myosoton aquaticum L. ( Liu et al, 2015 ), and Bromus tectorum L. ( Park and Mallory-Smith, 2004 ). Beckmannia syzigachne , biotypes with cross-resistance to ACCase and ALS inhibitor herbicides are frequently reported in China ( Li et al, 2013 ; Li et al, 2014 ; Li et al, 2015 ; Pan et al, 2015 ; Tang et al, 2015 ; Du et al, 2016 ; Liu et al, 2019 ; Wang et al, 2019 ). In addition, a biotype was also reported to have evolved multiple resistance to these kinds of herbicide ( Li et al, 2017 ).…”

“…For NTSR, metabolic genes related to resistance have been reported in fenoxaprop-P-ethylresistant B. syzigachne (Pan et al, 2016a;Pan et al, 2016b). However, to our knowledge, no studies have reported the involvement of genes in the NTSR mechanisms in B. syzigachne with ALS resistance, though the NTSR mechanisms have been confirmed (Wang et al, 2018;Wang et al, 2019;Bai et al, 2020). Furthermore, resistance genes relative to multiple resistance to ACCase and ALS-inhibiting herbicide have not been reported.…”

A Trp574Leu Target-Site Mutation Confers Imazamox Resistance in Multiple Herbicide-Resistant Wild Poinsettia Populations from Brazil

“…However, Trp574Leu is found in 96% of all species containing a SNP at the Trp574 The ALS enzyme assay has been used to complement whole-plant dose-response experiments in the investigation of ALS resistance in weeds [39]. Since this assay isolates the enzyme response in the presence of the herbicides, it can be used to predict potential target-site mutations [40,41]. For example, in tribenuron and imazamox resistant Rapistrum rugosum population, the RF at the enzyme level was greater than 270-fold, while the plant response in the greenhouse resulted in RF ranging from 40 to 370-fold [42].…”

Cytochrome P450 BsCYP99A44 and BsCYP704A177 Confer Metabolic Resistance to ALS Herbicides in Beckmannia syzigachne

“…American sloughgrass ( Beckmannia syzigachne ) is an annual grass weed and is often a problematic weed in wheat fields within a rice-wheat rotation [ 18 ], and mesosulfuron-methyl, an acetolactate synthase (ALS) inhibiting herbicide, is commonly used for control. To date, many studies showed that the continuous application of mesosulfuron-methyl to control B. syzigachne has led to the serious resistance problem [ 19 , 20 ]. Most resistance in B. syzigachne to mesosulfuron-methyl is due to target-site resistance [ 18 , 21 ], but cases of non-target-site resistance mechanisms exist and have not been clearly articulated.…”

“…In our previous study, a purified B. syzigachne biotype (R) without any known resistant mutations in the ALS gene showed 4.1-fold resistance to mesosulfuron-methyl based on GR 50 values and showed cross-resistant to pyroxsulam, imazethapyr, flucarbazone, and bispyribac-sodium. Further experimentation found the R biotype degraded more mesosulfuron-methyl than the susceptible biotype (S) [ 20 ]. Some cytochrome P450 genes such as CYP 704A177, CYP96B84 , CYP71D7 , CYP93A1, and CYP99A44 may be involved in the resistance of B. syzigachne according to RNA-Seq analyses.…”