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Mechanisms of Resistance to Pyroxsulam and ACCase Inhibitors in Japanese Foxtail (Alopecurus japonicus)

Feng Yujuan, Gao Yuan, Zhang Yong, Dong Liyao, Li Jun
Weed science 2016 v.64 no.4 pp. 695-704
Alopecurus, Brassica napus, Brassica rapa subsp. oleifera, Triticum aestivum, acetolactate synthase, acetyl-CoA carboxylase, annuals, cross resistance, dose response, genes, grass weeds, imidazolinone herbicides, in vitro studies, malathion, photosystem II, piperonyl butoxide, resistance mechanisms, sequence analysis, sulfonylureas, tetraploidy, wheat, China
Japanese foxtail is a predominant tetraploid grass weed in wheat and oilseed rape fields in eastern China. In China, pyroxsulam is mainly used to manage annual grass weeds, especially those resistant to acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides. Using dose–response studies, a pyroxsulam-resistant population, ACTC-1, was identified with a resistance index value of 58. Additionally, ACTC-1 was cross-resistant to sulfonylureas, imidazolinones, triazolopyrimidines, pyrimidinyl-benzoates, and sulfonylaminocarbonyl-triazolinones and multiresistant to ACCase and photosystem II inhibitors. Sequence analysis revealed four gene fragments encoding acetolactate synthase (ALS) from ACTC-1, and three from JNXW-1, a pyroxsulam-sensitive population. An Asp-376-Glu substitution was found in ALS1;2 and an Ile-2041-Asn in Acc1;1, which may be responsible for its resistance to pyroxsulam and ACCase inhibitors, respectively. In vitro assays of ALS activity revealed that in ACTC-1, the sensitivity of ALS to pyroxsulam was lower, and the basal ALS activity was twofold higher than that of sensitive population JNXW-1. Additionally, the combined application of pyroxsulam with malathion or piperonyl butoxide increased the sensitivity of ACTC-1 to pyroxsulam, although it could not completely overcome the resistance. It was inferred that both target-site-based resistance and nontarget-site-based resistance may be involved in the resistance to pyroxsulam.Nomenclature: Malathion; piperonyl butoxide (PBO); pyroxsulam; Japanese foxtail, Alopecurus japonicas Steud; birdsrape mustard, Brassica campestris L.; wheat, Triticum aestivum L.