No abstract

Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] is a problematic weed that grows in rice (Oryza sativa L.) fields. Over-applying herbicide caused environmental pollution and the emergence of resistant weeds, and integrated weed management method can reduce the dependence on herbicides. The growth of E. crus-galli and rice seedlings could be significantly inhibited by high concentrations of fulvic acid (FA, C14H12O8) under flooding conditions (HF, 0.80 g/L) (p < 0.05). In contrast, the growth of seedlings could be promoted by the application of very low-concentration FA (LF, 0.02 g/L). The activities of glutathione S-transferase (GSTs) and antioxidant enzymes, including total superoxide dismutase (T-SOD), peroxidase (POD), and catalase (CAT) in E. crus-galli seedlings were enhanced by LF treatment; while the POD activity was decreased, the GSTs, T-SOD, and CAT activities were not significantly changed by HF treatment. The metabolomic and transcriptomic analyses showed that FA regulated E. crus-galli seedling growth by affecting the synthesis of indole derivatives and flavonoid compounds. Compared with the blank control (CK, 0 g/L), the levels of four indole derivatives were up-regulated under HF treatment, and the indole derivatives mentioned above were slightly down-regulated under LF treatment. The flavonoids, including naringenin, naringenin chalcone, eriodictyol, kaempferol, and epigallocatechin, were down-regulated under HF treatment, and the growth of E. crus-galli was restrained. In contrast, the metabolism and transcription of flavonoids were not significantly changed under LF treatment. Under the addition of 0.80 g/L FA, the growth of newly sprouted E. crus-galli was obviously inhibited, and the growth of rice was significantly promoted after eight days of rice planting (p < 0.05). The application of FA, therefore, might be a potential integrated weed management method to control the damage caused by E. crus-galli in paddy fields.

Botanical compounds with herbicidal activity exhibit safety, low toxicity, and low chances of herbicide resistance development in plants. They have widespread applications in green agricultural production and the development of organic agriculture. In the present study, dihydrocoumarin showed potential as a botanical herbicide, and its phenotypic characteristics and mechanism of action were studied in barnyardgrass [Echinochloa crus-galli (L.) P.Beauv.] seedlings. The results indicated that dihydrocoumarin inhibited the growth of barnyardgrass without causing significant inhibition of rice seedling growth at concentrations ranging between 0.5 and 1.0 g/L. Additionally, dihydrocoumarin treatment could cause oxidative stress in barnyardgrass, disrupt the cell membrane, and reduce the root cell activity, resulting in root cell death. Transcriptomic analyses revealed that dihydrocoumarin could inhibit barnyardgrass normal growth by affecting the signal transduction of plant hormones. The results showed significant differential expression of plant hormone signal transduction genes in barnyardgrass. Additionally, dihydrocoumarin interfered with the expression of numerous phenylpropanoid biosynthesis genes in barnyardgrass that affect the production of various vital metabolites. We speculate that the barnyardgrass growth was suppressed by the interaction among hormones and phenylpropanoid biosynthesis genes, indicating that dihydrocoumarin can be applied as a bioherbicide to control barnyardgrass growth in rice transplanting fields.

Barnyardgrass (Echinochloa crus-galli L.) is the most serious weed threatening rice production, and its effects are aggravated by resistance to the quinclorac herbicide in the Chinese rice fields. This study conducted a comparative proteomic characterization of the quinclorac-treated and non-treated resistant and susceptible E. crus-galli using isobaric tags for relative and absolute quantification (iTRAQ). The results indicated that the quinclorac-resistant E. crus-galli had weaker photosynthesis and a weaker capacity to mitigate abiotic stress, which suggested its lower environmental adaptability. Quinclorac treatment significantly increased the number and expression of the photosynthesis-related proteins in the resistant E. crus-galli and elevated its photosynthetic parameters, indicating a higher photosynthetic rate compared to those of the susceptible E. crus-galli. The improved adaptability of the resistant E. crus-galli to quinclorac stress could be attributed to the observed up-regulated expression of eight herbicide resistance-related proteins and the down-regulation of two proteins associated with abscisic acid biosynthesis. In addition, high photosynthetic parameters and low glutathione thiotransferase (GST) activity were observed in the quinclorac-resistant E. crus-galli compared with the susceptible biotype, which was consistent with the proteomic sequencing results. Overall, this study demonstrated that the resistant E. crus-galli enhanced its adaptability to quinclorac by improving the photosynthetic efficiency and GST activity.