Impact of foliar potassium fertilization on biochemical composition and antioxidant activity of fig (Ficus carica L.)

The metabolic processes involved in fig production are influenced by macro- and micronutrients supply to the trees during the growing season. Potassium is an essential plant nutrient that influences growth and fruit quality. In this study, the effect of foliar potassium sulphate (K2SO4) application on biochemical composition and antioxidant activity of fig was assessed in cv. Bouhouli, a commonly cultivated cultivar in Djebba (Northwest of Tunisia). Foliar potassium sulphate supply at 2% on Bouhouli trees were applied twice during the fruit growth. Results exhibited that potassium fertilization induces a significant change in total phenolic, flavonoid contents and radical scavenging activity in total fruit and achenes compared to the control. A strong correlation was observed between antioxidant activity and different phenolic compounds. The total fruit and achenes methanol extracts possess, respectively, the highest values of polyphenol by 29.3 and 25.1 mg GAE/g DW compared to the control. Similarly, the flavonoids content was increased in methanol extracts, respectively, by 36 and 48%. HPLC analyses revealed the influence of potassium on concentrations of phenolic compounds in fig sprayed with K2SO4. Among the polyphenols, the chlorogenic acid, cyanidin 3-rutinoside and cyanidin 3,5-diglucoside contents increased from 0.87 to 1.70 mg/g DW under potassium spray, whereas those compounds were not detected in fig achenes. The present study provides clear evidence that potassium sulphate can be used to manipulate total phenolic concentrations in fig with strong antioxidant potential that could be benefits to human health. Thus, potassium sulphate application at 2% could improve nutritional and qualitative attributes of fig.