Variation in secondary metabolites contents of Spinoso Sardo artichoke (Cynara cardunculus L.) under different day lengths

Globe artichoke (Cynara cardunculus L. var. scolymus Fiori) is an economically important crop in the Mediterranean basin and particularly in Italy, which is a leading producer. In this research, we studied the effect of extended photoperiod (15 and 17 h) on polyphenolic, flavonoids, lignin concentrations, and antioxidant activity in edible and inedible organs of artichoke. The influence of day length on morphological traits and biomass accumulation was also assessed. The total phenolic content of whole plants grown under natural day length conditions exceeds that of photoperiod extended for 15 and 17 h by 31% and 32.4%, respectively. The decrease of total phenols was high in inner bracts at photoperiods of 15 and 17 h, whereas the differences among treatments in receptacle were negligible. Antioxidant activity and total flavonoids followed the same trend observed for total phenols. The amount of lignin was dependent on the tissue. In the control, the content of lignin ranged from 0.4 to 2.8 g/100 g of dry weight in receptacle and leaves of rosette, whereas in the 15-h treatment, it ranged from 0.3 to 5.1 g/100 g DW in floral steam and leaves of peduncle, respectively. Fifteen-hour day length significantly reduced the lignin content in receptacle and floral stem. Head morphology was little influenced by photoperiod, whereas significant differences were obtained in floral stein diameter, showing larger values in natural conditions compared to photoperiodic treatments. C and N were also affected by photoperiod.