Effect of shading on the sesquiterpene lactone content and phytotoxicity of cultivated cardoon leaf extracts

The work described here follows on from a previous study focused on the influence of the genotype and harvest time on the sesquiterpene lactone (STL) profile of Cynara cardunculus L. leaf extracts. The aim of this study was to investigate the effect that 60% plant shading in cultivated cardoon (C. cardunculus var. altilis) leaf extracts harvested in winter and spring had on the composition of STLs and the phytotoxicity. The phytotoxicity of leaf extracts was evaluated by assessing wheat coleoptile elongation along with seed germination and the root and shoot length of the weeds Amaranthus retroflexus L. and Portulaca oleracea L. Shading increased the production of STLs in spring, and this effect correlated positively with the phytotoxic activity. The induction of shading can therefore be used to modulate STL concentrations and their phytotoxic potential in cultivated cardoon leaves for industrial applications.