STL concentration and composition.
Yields of extracts, calculated as [(g extract/ g dried leaves)·100], were 14.8 and 24.1% for Control (’Bianco gigante’ without stress), and 13.3 and 25.0 % for stressed ’Bianco gigante’ in January and April harvest, respectively. The interaction “light stress × harvest time” was highly significant for all STLs and the latter factor, in particular, more contributed than stress condition to the analysis of variance for the total concentration (F =637) and for all the STLs (Table 1). Light stress significantly affected STL concentrations, with an increase of 338, 102, 94 and 35% in the April harvest of cynaratriol, deacylcynaropicrin, 11,13-dihydro-deacylcynaropicrin and grosheimin, respectively, compared to control (Figs. 2 and 3). A higher concentration in the control was registered only in aguerin B. April harvest showed the highest concentration for both total and single STLs, except for grosheimin, deacylcynaropicrin and 11,13-dihydro-deacylcynaropicrin controls. The effect of harvest time was more marked if combined with the light stress. For instance, an increase of 221, 190 and 703% was registered from January to April in the total, cynaropicrin and cynaratriol concentrations, respectively (Fig. 2). Overall, cynaropicrin was the predominant STL of cultivated cardoon leaf extracts (70 and 73 mg L−1 in April harvest of control and light stress, respectively), followed by cynaratriol (14.9 mg L−1 in April harvest of light stress). Among minor STLs, aguerin B was the most abundant even if with higher values in the control (3.6 mg L−1 in April harvest).