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Eleusine indica is a typical xerophytic weed species with a cosmopolitan distribution. It is invasive and highly adaptable to diverse habitats and crops. Due to rice cropping-pattern changes, E indica has become one of the main dominant grass weeds infecting direct-seeding paddy fields. A Chinese E. indica population has evolved multiple-herbicide resistance to cyhalofop-butyl and glyphosate. In this study, the multiple-resistance profile of E. indica to these two different types of herbicides and their resistance mechanisms were investigated. Whole-plant dose–response assays indicated that the multiple-herbicide-resistant (MHR) population exhibited 10.8-fold resistance to cyhalofop-butyl and 3.1-fold resistance to glyphosate compared with the susceptible (S) population. ACCase sequencing revealed that the Asp-2078–Gly mutation was strongly associated with E. indica resistance to cyhalofop-butyl. The MHR plants accumulated less shikimic acid than S plants at 4, 6, and 8 days after glyphosate treatment. In addition, no amino acid substitution in the EPSPS gene was found in MHR plants. Further analysis revealed that the relative expression level of EPSPS in MHR plants was 6–10-fold higher than that in S plants following glyphosate treatment, indicating that EPSPS overexpression may contribute to the glyphosate resistance. Furthermore, the effectiveness of nine post-emergence herbicides against E. indica were evaluated, and one PPO inhibitor pyraclonil was identified as highly effective in controlling the S and MHR E. indica populations.

Bearded sprangletop [Diplachne fusca (L.) P. Beauv. ex Roem. & Schult. ssp. fascicularis (Lam.) P. M. Peterson & N. Snow] is a noxious annual grass weed of paddy fields, distributed in coastal regions of the Jiangsu and Hebei provinces in China. Cyhalofop-butyl has been widely used to control grass weeds since 2006 in China. Overreliance on cyhalofop-butyl has led to the evolution of resistant weeds. In this study, the resistance level and cyhalofop-butyl resistance mechanisms were investigated in the putative resistant (JSHH) population. The dose–response experiments showed that the JSHH D. fusca population had evolved 8.9-fold resistance to cyhalofop-butyl. Acetyl-CoA carboxylase (ACCase) sequencing revealed a point mutation (GGC to GCC) at amino acid position 2096, resulting in a Gly-2096-Ala substitution in the resistant population. To our knowledge, this is the first case of cyhalofop-butyl resistance in D. fusca and the first report of a target-site mutation conferring resistance to ACCase-inhibiting herbicides in D. fusca. In addition, the resistant D. fusca population (JSHH) with the Gly-2096-Ala mutation was cross-resistant to the aryloxyphenoxypropionate herbicide metamifop, the cyclohexanedione herbicide sethoxydim, and the phenylpyrazolin herbicide pinoxaden.

Catchweed bedstraw (Galium aparine L.) is a problematic dicot weed that occurs in major winter wheat (Triticum aestivum L.) fields in China. Tribenuron-methyl has been widely used to control broadleaf weeds since 1988 in China. However, overuse has led to the resistance evolution of G. aparine to tribenuron-methyl. In this study, 20 G. aparine populations collected from Shandong and Henan provinces were used to determine tribenuron-methyl resistance and target-site resistance mechanisms. In dose–response experiments, 12 G. aparine populations showed different resistance levels (2.92 to 842.41-fold) to tribenuron-methyl compared with the susceptible population. Five different acetolactate synthase (ALS) mutations (Pro-197-Leu, Pro-197-Ser, Pro-197-His, Asp-376-Glu, and Trp-574-Leu) were detected in different resistant populations. Individuals heterozygous for Pro-197-Ser and Trp-574-Leu mutations were also observed in a resistant population (HN6). In addition, pHB4 (Pro-197-Ser), pHB7 (Pro-197-His), pHB8 (Pro-197-Leu), pHB5 (Asp-376-Glu), and pHB3 (Trp-574-Leu) subpopulations individually homozygous for specific ALS mutations were generated to evaluate the cross-resistance to ALS-inhibiting herbicides. The pHB4, pHB7, pHB8, pHB5, and pHB3 subpopulations all were resistant to sulfonylurea, pyrazosulfuron-ethyl, triazolopyrimidine, flumetsulam, sulfonylamino-carbonyl-triazolinone, flucarbazone-sodium, pyrimidinyl thiobenzoate, pyribenzoxim, and the imidazolinone imazethapyr. These results indicated the diversity of the resistance-conferring ALS mutations in G. aparine, and all these mutations resulted in broad cross-resistance to five kinds of ALS-inhibiting herbicides.

Sublethal concentrations of chlorantraniliprole might upregulate the expression of JH biosynthesis genes and in turn result in an increase of JH level in C. suppressalis. © 2017 Society of Chemical Industry.

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