Allelopathic effects of Cynara cardunculus L. extracts

Abstract

Weeds are recognized as the most important biotic factor affecting yields in agroecosystems. The negative effects derived from the irrational use of herbicides have led to an increasing interest to eco-friendly practices for weed control, including the manipulation of allelopathic mechanisms. The present study aims to explore the potential use of Cynara cardunculus L. leaf extracts for the biological control of weeds and pathogen microorganisms. In a first trial, the allelopathic effects of its leaf aqueous extracts were demonstrated on seed germination of six common weeds. Secondly, the set-up of the most efficient extraction method of its allelochemicals in terms of costs, yields and inhibitory activity was realized, selecting dried leaves as the best plant material and ethanol and ethyl acetate as the best solvents. Moreover, new C. cardunculus allelochemicals (cynaratriol, desacylcynaropicrin, 11,13-dihydro-desacylcynaropicrin and pinoresinol) were purified. Third, the effect of genotype, harvest time and light stress (by plant shading) was evaluated on the phytotoxicity, quantity and composition of sesquiterpene lactones in C. cardunculus leaf extracts through a new UHPLC-MS/MS analysis method. Wild and cultivated cardoon showed the highest concentrations, while spring was the best harvest time. Moreover, light stress stimulated the synthesis of these allelochemicals. In a second trial, the effects resulting from 3-years cultivation, in two different areas, with globe artichoke, cultivated and wild cardoon were studied on the quali/quantitative composition of the weed soil seed bank and on soil eubacterial communities. In both areas, C. cardunculus reduced the weed seed bank size compared to controls. Nevertheless, the presence of cultivated cardoon had a negative influence towards Bacillus subtilis and a positive one on Pseudomonas putida and Azospirillum brasilense. Lastly, cultivated cardoon leaf extracts were assessed in vitro for the control of several microorganisms of agriculture and food interest. All the extracts showed an important antimicrobial activity, especially when using ethanol as extracting solvent.