Abstract
The present study aimed to investigate the influence of repeated preharvest application of zinc (Zn), silicon (Si), molybdenum (Mo) and amino acids on fruit quality of Jonathan apples (Malus x domestica Borkh). The trial was conducted in 2016 in an organic orchard at the Research Centre Laimburg in South Tirol (Italy), with seven-year-old ‘Jonathan’ apple trees on M9 rootstock. Canopy applications of a balanced mix of amino acids, amino acids combined with zinc (AA+Zn) and a commercial product containing Si, Zn, Mo (Siliforce®) were performed at weekly interval, starting from the end of May (about 40 DAFB) until mid-August. Fruit quality parameters such as fruit weight, colour characteristics, fruit firmness, soluble solids content (SSC), titratable acidity, starch conversion, total phenolics, anthocyanins and the physiological disorder ‘Jonathan spot’ were evaluated at harvest and monitored during storage at 2°C in normal atmosphere conditions. Treatments had a significant impact on the ripening of fruits, showing significantly lower SSC (-7%), higher acidity (+12%) and starch content compared to control. Despite treated fruits being generally less ripe, the extension of red over-colour was not different when compared to controls. Moreover, results showed that the synthesis of phenolic compounds was favoured by foliar applications. The content of total phenols was significantly enhanced in peel of fruits treated with AA+Zn, whereas anthocyanins were not significantly affected by treatments. The physiological disorder was not present at harvest. After 3 weeks of storage, results indicated that ‘Jonathan spot’ was significantly reduced in fruits treated with AA+Zn and Siliforce® (-78%, compared to control). First results of our study indicate that preharvest foliar application of Zn with amino acids might be recommended to control ripening dynamic of Jonathan apples while improving their overall phenolic content at harvest. Furthermore, the application of AA+Zn reduced the incidence of the ‘Jonathan spot’ symptoms during storage, enhancing the rate of marketable fruits.