IMPROVING QUALITY AND STORABILITY OF APPLES BY A COMBINATION OF ALUMINUM REFLECTIVE MULCH, SUMMER PRUNING AND CONTROLLED NITROGEN FERTILIZATION

‘Aroma’ and ‘Ingrid Marie’ are the most important adapted apple cultivars to the Swedish conditions. Poor coloration at optimum harvest date and weak resistance to Pezicula malicorticis limit growers’ ability to meet quality standards. In a three-year study at the Kivik research station, a novel orchard management model of; covering ground with aluminum (“reflective mulch” during 4 weeks before harvesting), cut thinning (to leave 6 fruits per cm2 trunk cross-sectional area “TCSA” in July) and fertilizing according to leaf nitrogen-content, was applied to improve the quality and storage potential of these two cultivars. Tree yield and productivity were estimated. Apples were picked at pre-climacteric period and stored in three different storage methods (air: 21.0 kPa O₂ + 0.03 CO₂ kPa, control atmosphere storage 2.5 kPa O₂ + 2.5 kPa CO₂, and ultra low oxygen atmosphere ‘ULO’: 1.0 kPa O₂ + 2.0 kPa CO₂), and on 2.0°C, 90% RH for 22 weeks, before they were held in shelf life on 18°C, 90% RH for an additional week. Fruit color, firmness, soluble solids concentration (SSC), titratable acidity (TA) and antioxidant compounds (ascorbic acid, total phenols and anthocyanin) were investigated at harvest and after shelf life. The applied combined model significantly increased fruits color (lower hue angle and higher C* value) in comparison with the standard managed trees. The applied combined model also caused higher yield by 25%, larger fruit by 16-17%, better flesh firmness by 10%, and higher TA/SSC content by 25% in comparison with classic management. The fruit storability of these two cultivars was improved whereas higher resistance to bull’s eye rot (Pezicula malicorticis) by 77% in ‘Aroma’ and 57% in ‘Ingrid Marie’ apples were achieved and the quality was better maintained, particularly in ULO storage. This novel management model increased anthocyanin and total phenol content in both cultivars.