Exploring Cynara cardunculus L. as a botanical alternative to chemical herbicides for weed management

Cynara cardunculus L. demonstrates phytotoxic properties on weeds through various compounds, including sesquiterpene lactones such as cynaropicrin, as well as flavonoids like luteolin and apigenin, identified as responsible for these effects. Among these compounds, cynaropicrin has garnered particular attention due to its significant allelopathic effects, notably a strong inhibition of plant growth
(Scavo et al., 2019). On the other hand, it has recently been demonstrated that the application of a methanolic extract of Cynara cardunculus L. inhibits weed germination, reduces seedling growth, and induces necroses and chloroses, attributed to the presence of various secondary metabolites, in
particular, myricitrin (Ben Kaab et al., 2020) and cynaropicrin (unpublished results). These compounds exhibit a significant phytotoxic effect comparable to commercial bioherbicides containing pelargonic acid (Ben Kaab et al., 2020). During previous studies, conventional extraction methods were widely favored due to their simplicity and efficiency. These methods involve the use of organic solvents such as methanol, ethanol, ethyl acetate, and chloroform. However, this approach comes with drawbacks, including potential health risks and the persistence of solvent residues in the final products, requiring additional purification that makes the process longer and increases the costs of obtaining the molecules of interest. Moreover, it
has limitations in extracting polar compounds, such as phenolic acids (Arceusz, Wesolowski, and Konieczynski, 2013; Khoddami, Wilkes, and Roberts, 2013). Various alternative options, including ultrasound-assisted extraction, microwave-assisted extraction, and supercritical CO2 extraction, have garnered considerable attention for research conducted in other fields (Ajila et al., 2011).
We have initiated greenhouse experiments to assess the efficacy of Cynara cardunculus extracts on weeds. The extracts, obtained using methanol, ethyl acetate, and chloroform from Cynara cardunculus L., have shown promising results. Notably, the ethyl acetate extracts demonstrated a particularly high
level of efficiency. Simultaneously, we conducted UPLC analyses to identify potential molecules responsible for the herbicidal effect across three Cynara cardunculus genotypes. We extended these analyses to include both methanol and ethyl acetate extracts. Our findings confirmed the presence of cynaropicrin, which is considered the fingerprint molecule of Cynara cardunculus L., in all extracts. However, varying
concentrations of cynaropicrin were observed, with the highest concentration detected in the ethyl acetate extract. This preliminary data suggests a correlation between the efficacy of the extracts and the concentration of cynaropicrin. Further investigations will delve into optimizing extraction methods to enhance cynaropicrin content and identify other secondary metabolites potentially responsible for this effect, ultimately maximizing the herbicidal potential of Cynara cardunculus extracts on weeds