Utilization of Cynara cardunculus L. allelopathic activity for weed control

In the last decades, the increasing search in eco-sustainable strategies for weed management, has led the scientific community to explore the utilization of plant secondary metabolites, commonly called allelochemicals, in agriculture. Recently, Cynara cardunculus L., a perennial herbaceous plant belonging to Asteraceae family, has been studied for its allelopathic activity caused by sesquiterpene lactones such as cynaropicrin, aguerin B and grosheimin (1), and by polyphenols such as chlorogenic acid, luteolin- and apigenin derivatives, both presented in high quantities in the leaves. In a first step the phytotoxic activity of aqueous leaf extracts (40 and 80% concentrations) of globe artichoke [var. scolymus (L.) Fiori], cultivated cardoon (var. altilis DC.), and wild cardoon [var. sylvestris (Lamk) Fiori] (Fig. 1) was evaluated on seed germination and mean germination time of six weed species (Amaranthus retroflexus L., Diplotaxis erucoides (L.) DC., Portulaca oleracea L., Lavatera arborea L., Brassica campestris L. and Solanum nigrum L.) widespread in Mediterranean Basin, along with the autoallelopathic activity of wild cardoon (2). Effects varied with the weed species and the extract concentrations. The results showed a mean reduction of about 41% in germination of all test species in comparison with the controls and the best result was obtained with the leaf extracts (80%) of cultivated cardoon, which resulted the most efficient also in comparison with wild cardoon, allowing only 9% of seed germination.Since cultivated cardoon extract resulted the most phytotoxic among the three botanical varieties, it was further investigated. In particular, the inhibitory activity of leaves (fresh, dried and lyophilized) of cultivated cardoon, treated with three different solvents (bidistilled water, 70% methanol and 80% ethanol) in presence/absence of citric acid (20%), on four common Mediterranean weed species (A. retroflexus, P. oleracea, Stellaria media (L.) Vill., and Anagallis arvensis L.) was compared (3). On the average of the four weed species under study, all leaf extracts showed inhibitory effects. Regarding plant material, lyophilized leaves permitted only 3.2% of seed germination as compared to 73% of control, followed by dried leaves (10%) and fresh leaves (16%). For what concern the solvents, the ethanolic extracts completely inhibited weed seed germination, while bidistilled water was the least effective (34% vs 73% of control) compared to the other solvents. Moreover, the polyphenolic profile of dried leaves aqueous, methanolic and ethanolic extracts of cultivated cardoon were analysed by HPLC. Results showed that the highest total measured polyphenols was found in the MeOH extract (14727 mg kg-1 of DM), followed by EtOH one (10561 mg kg-1 of DM) and aqueous extract (2777 mg kg-1 of DM), with caffeoylquinic acids representing more than 50% of the total measured polyphenols. These results suggest that C. cardunculus extracts can be used for the potential production of a bioherbicide.