Echinochloa crus-galli (L.) P. Beauv (common name: barnyard grass) is a major weed in rice-growing areas and has evolved resistance to multiple herbicides. Florpyrauxifen-benzyl (trade name Rinskor) is a novel synthetic auxin herbicide that was approved in China in 2017 and is widely used in rice production to control resistant weeds, including barnyard grass. We identified a florpyrauxifen-benzyl-resistant E. crus-galli biotype with a resistance index (RI) of 11.89 using screen house herbicide experiments. To understand the phytotoxicity mechanisms of florpyrauxifen-benzyl, we used transcriptomics technologies to compare the gene expression profiles of florpyrauxifen-benzyl treatment on phytohormone transduction between florpyrauxifen-benzyl-resistant and -susceptible barnyard grasses (Echinochloa crus-galli (L.) P. Beauv). A total of 1810 DEGs were identified in the S comparison setting (FTS vs. UTS), and 915 DEGs were identified in the R comparison setting (FTR vs. UTR); 464 genes overlapped between the two comparison groups. Approximately sixty-nine hormone-related DEGs were detected after treatment with florpyrauxifen-benzyl in both R and S biotypes. At 24 h after florpyrauxifen-benzyl treatment, compared with the R biotype, the S biotype showed a stronger auxin response and higher expression of related genes involved in ethylene and abscisic acid biosynthesis and signal transduction. In addition, a brassinolide receptor gene was upregulated after florpyrauxifen-benzyl treatment and had higher expression in the S biotype than in the R biotype. This study is the first transcriptome analysis of the differential effects of florpyrauxifen-benzyl treatment between florpyrauxifen-benzyl-resistant and -susceptible E. crus-galli. It reflects the difference in phytohormone biosynthesis and signal transduction between R and S barnyard grasses in response to florpyrauxifen-benzyl treatment and will be helpful for understanding the phytotoxicity mechanisms of florpyrauxifen-benzyl.

Roegneria kamoji Ohwi (Poaceae), a wild relative plant of wheat which is widely distributed across China, has become a dominant and problematic weed in wheat fields in some regions. We have previously confirmed that R. kamoji is highly tolerant to foliar-applied acetyl-CoA carboxylase (ACCase) and acetolactate synthase (ALS) inhibitors in wheat (Triticum aestivum L.). The sensitivity of R. kamoji to pre-emergence (PRE) herbicides and the basis of fenclorim increase selectivity to butachlor between wheat and R. kamoji were evaluated in this study. Screenhouse bioassay showed that R. kamoji exhibited similar sensitivity to wheat to PRE herbicides at their recommended field doses (RFD); it also showed that buatchlor provides the highest relative control for R. kamoji (53.4% emergence and 81.5% fresh weight reduction, respectively), while it had no impact on seedling emergence of wheat among the six PRE herbicides. When butachlor was applied at four-fold RFD, no R. kamoji seedlings emerged; however, it significantly reduced the above-ground biomass of wheat compared with the non-treated control. Pre-treatment with herbicide safener fenclorim by seed soaking increased the ED10 value of butachlor to wheat from 221.8 to 1600.1 g a.i. ha−1, thus increasing the selectivity index from 9.6 to 68.9 between wheat and R. kamoji. The activities of α-amylase activity and protein content during germination, and glutathione-S-transferase (GST) and β-ketoacyl-CoA synthase (KCS) in the seedlings, could be induced by butachlor in both wheat seeds with or without fenclorim pre-soaking. These results suggested that butachlor provides the highest control for R. kamoji and did not affect germination and emergence in wheat. The basis of fenclorim-increased selectivity to butachlor was associated with the induced GST and KCS-mediated enhanced herbicide metabolism in wheat.

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