SUMMARY
Intensive agriculture needs new sustainable tools for weed management.
In recent years, allelopathy offered a valid alternative. Sesquiterpene
lactones (STLs) are the most important cultivated cardoon (Cynara
cardunculus L. var. altilis DC.) allelochemicals involved in
weed toxicity. The present study aims to investigate the effect of field
light stress (by 60% of plant shading) on the qualitative and
quantitative composition of STLs in cultivated cardoon leaf extracts
harvested in January and April. The phytotoxicity of leaf extracts was
evaluated on the wheat coleoptile elongation, seed germination, root and
shoot length of the weeds Amaranthus retroflexus L. andPortulaca oleracea L. Light stress significantly increased the
concentrations of total and single STLs, and this increase was more
marked if combined with harvest time (+338, 102 and 94 of cynaratriol,
desacylcynaropicrin and 11,13-dihydro-deacylcynaropicrin, respectively)
in April. The concentration of STLs and the phytotoxic activity were
correlated (light stressed extracts belonging from April reduced by 91,
86 and 93% the wheat coleoptile elongation and the root and shoot
length of A. retroflexus , respectively, at 800 ppm). Therefore,
the induction of light stress could be used to increase the
concentrations of STLs in cultivated cardoon leaves for industrial
applications and to improve their phytotoxic potential.