Investigating the Allelopathic and Bioherbicidal Potential of Solidago altissima with a Focus on Chemical Signaling in Trifolium repens

Abstract

Invasive weed species exhibit both advantages, such as the potential for allelochemicals in bioherbicide development, and risks, including their threat to crop production. Therefore, this study aims to identify an allelochemical from Solidago altissima, an invasive weed species. The dose-dependent effects of S. altissima shoot and root extracts (SSE, SRE) on the signaling in the forage crop Trifolium repens and germination in various weed species (Echinochloa oryzicola, Cyperus microiria, Alopecurus aequalis, Portulaca oleracea, and Amaranthus retroflexus) were evaluated. The results showed that the T. repens seedlings treated with root extracts exhibited a significant decrease in plant height, dry weight, and chlorophyll content, along with an increase in H₂O₂ levels. Additionally, antioxidant activities, such as superoxide dismutase, catalase, and peroxidase enzyme activities, were significantly elevated in T. repens treated with SRE. Moreover, SRE treatment significantly inhibited the seed germination of all tested weed species in a concentration-dependent manner. Gas chromatography-mass spectrometry analysis of S. altissima root extract identified a high concentration of methyl kolavenate, a clerodane diterpene predicted to act as a phytotoxic agent. These findings highlight the potential of S. altissima for the development of crop-protective agents while emphasizing its potential risks in agriculture.

Keywords: ROS; antioxidants; methyl kolavenate; phytohormone; phytotoxicity; weeds.

Figure 1

(A) Screening of the effects of SSE and SRE extracts on T. repens seedlings. (B) IC₅₀ values of SSE and SRE extracts. The bars represent the mean ± standard deviation (SD) (n = 3). Significant differences among treatments are indicated by different letters (a–e) based on Duncan’s multiple range test (DMRT, p < 0.05). The IC₅₀ value for each treatment was calculated based on the fresh weight of T. repens seedlings. Statistical significance was determined using a t-test (** p < 0.01).

Figure 2

Dose-dependent effects of SRE on morphological variations in T. repens (A) Visual differences. (B) Shoot length. (C) Root length. (D) Fresh weight. (E) Chlorophyll content. Error bars represent the mean ± standard deviation (SD) (n = 5). Letters a–c denote significant differences (p < 0.05) using Duncan’s multiple range test (DMRT).

Figure 2

Dose-dependent effects of SRE on morphological variations in T. repens (A) Visual differences. (B) Shoot length. (C) Root length. (D) Fresh weight. (E) Chlorophyll content. Error bars represent the mean ± standard deviation (SD) (n = 5). Letters a–c denote significant differences (p < 0.05) using Duncan’s multiple range test (DMRT).

Figure 3

Effect of SRE treatment on H₂O₂ accumulation in T. repens seedlings, visualized using DAB staining. H₂O₂ concentrations in T.repens seedlings increased in the following order: TR5 > TR4 > TR3 > TR2 > TR1.

Figure 4

Reactive oxygen species (ROS) content in T. repens seedlings after SRE treatment. (A) O₂⁻ content. (B) H₂O₂ content. Bars and error bars represent the mean ± standard deviation (SD), (n = 3). Different letters denote significant differences (p < 0.05), as determined using Duncan’s Multiple Range Test (DMRT).

Figure 5

Effect of S. altissima extract treatment on soluble protein content and antioxidant activity in T. repens. (A) Soluble protein, (B) superoxide dismutase (SOD), (C) catalase (CAT), and (D) peroxidase (POD) activity. Bars and error bars represent the mean ± standard deviation (SD), (n = 3). Letters above the bars denote significant differences (p < 0.05), determined using Duncan’s Multiple Range Test (DMRT).

Figure 6

Effect of S. altissima extract treatment on phytohormone content in T. repens. (A) ABA, (B) SA, and (C) JA. Bars and error bars represent the mean ± standard deviation (SD), (n = 3). Letters denote significant differences (p < 0.05) determined using Duncan’s multiple range test (DMRT).

Figure 7

Chemical structure of the predominant compound, methyl kolavenate, identified in the extract.

Figure 8

Effect of SRE treatment on the germination of different weed species: (A) E. oryzicola, (B) C. microiria, (C) A. aequalis, (D) P. oleracea, and (E) A. retroflexus.

Figure 9

(A) Curve illustrating the germination inhibition rate (GIR) of T. repens after treatment with the CHCl₃ fraction, with an IC₅₀ of 676.3 mg/L. Error bars represent the standard deviation (SD) (n = 3). (B) Schematic diagram of the liquid–liquid extraction process and fraction distribution of SRE. (C) Visual observation of the dose-dependent effect of CHCl₃ fraction treatment on SRE in T. repens germination.

Figure 10

Dose-response inhibition curves illustrating germination inhibition rate (GIR) of T. repens for chromatography fractions with the highest IC₅₀ values. (A) Dose-response inhibition curve of fraction CA. (B) Dose-response inhibition curve of fraction CAE. Error bars represent the standard deviation (SD) (n = 3). Visual observation of the dose-dependent effects of different SRE fractions on T. repens germination (C). Figure 1 details the fractionation methodology.