Foliar Application of Phosphorus Improves Apple Fruit Color During Ripening

The red color of skin is a much desired property in apple production. For better red fruit coloration the applications of foliar fertilizers on the basis of calcium and phosphorus are used. In the present study ‘Braeburn’ apple trees were sprayed twice with Phostrade Ca (phosphorus), 5 and 3 weeks before harvest. In 7-days intervals fruit color, the content of flavonoids and enzyme activity involved in the synthesis of anthocyanins have been monitored. Foliar application of Phostrade Ca caused a more intense red skin color of apples and higher anthocyanin content. Their level increased during ripening, in treated apples the content of total anthocyanins was 20-fold higher at harvest while in control apples only 9-fold higher compared to the initial values. Cyanidin 3-galactoside was the most abundant anthocyanin (80 to 86% of total anthocyanins), followed by cyanidin 3-arabinoside, cyanidin 3-glucoside, cyanidin 3-xyloside and cyanidin 7-arabinoside. Prostrade Ca increased the levels of all quercetin glycosides, with the exception of quercetin 3-rhamnoside. No significant influence of Phostrade Ca on the content of hydroxycinnamic acids, dihydrochalcones, flavanols and total phenolics has been monitored. The activity of FHT and DFR increased during ripening but Phostrade Ca influenced only higher activity of DFR.