Evaluation of Fruit Quality, Chromatic Parameters and Anthocyanin’s Content Under Foliar Application of Magnesium and Potassium on Sweet Cherry (Prunus avium L.) cv. Burlat ^†

Sweet cherries are seasonal fruits, considered one of the most popular spring and summer fruits in temperate regions of Europe due to their attractive appearance, taste, colour and sweetness, having a high economic importance.

In the North of Portugal, the Resende region is the main area responsible for the total cherry production due to their excellent edaphoclimatic conditions. Thus, potassium (K) and magnesium (Mg) nutrients were applied at the foliar level in sweet cherry trees (cv. Burlat) in an orchard located in the Resende region, at low and high doses (50 g/hL⁻¹ and 100 g/hL⁻¹ of K (Enermax—potassium oxide, K₂O), 125 g/hL⁻¹ and 250 g/hL⁻¹ of Mg) and control treatment (100 g/hL⁻¹ of K and 250 g/hL⁻¹ of Mg), with the aim to increase cherry quality by crop nutrition. Using fruits harvested in May 2020, at their commercial ripening stage, this study intended to analyse the parameters related to fruit quality as biometric parameters, total soluble solids (TSS), pH, titratable acidity (TA) and maturity index (TSS/TA), as well as chromatic parameters. The anthocyanin’s content was also determined by a pH differential method.

In general, the control treatment presented fruits with a higher weight and size, while fruits treated with potassium at a high dose had lower values. Regarding TSS, pH, TA and TSS/TA, the values were similar among all treatments. However, TSS was lower and TA was higher in cherries treated with a high dose of potassium, which means that this treatment provoked a delay in fruit maturation (the maturity index was lower). The opposite occurred in cherries treated with a lower dose of potassium (higher TSS and lower TA means higher TSS/TA; therefore, anticipating fruit harvest). Concerning chromatic parameters, higher values were obtained in cherries treated with a high dose of potassium, which means lighter cherries, while lower values were found in the treatment with a low dose of magnesium and, consequently, indicate darker and redder cherries. These results can also be correlated with anthocyanin’s content, as cherries treated with a high dose of potassium presented the lowest anthocyanin content and cherries treated with a low dose of magnesium had the highest anthocyanin content.