**4. Materials and Methods**

## *4.1. Plant Material*

Leaves and apples were harvested in 2019, at two different locations, in the experimental orchard Brdo pri Lukovici (L1: Continental Slovenia; 46◦10'04.8" N, 14◦40'55.2" E, altitude 368 m) and in the north-west part of Slovenia, in Sadovnjak Resje (L2: Latitude 46◦20" N, longitude 14◦12" E, altitude 500 m). Soils on location L1 are Dystric cambisol on fine sediments (clay and silt) with pH = 4.8 (0.01 M CaCl2) and organic carbon content 2.1% (Corg) in top 30 cm. On location L2, soils are deep (Eutric cambisol) with a similar organic carbon content (Corg = 2.4%) but not so acidic (pH= 5.8) top soil. Weather conditions on both locations during the vegetation period in 2019 are presented in Table S10 and Figure S4. The amount of precipitation was very similar on both locations (731 mm on L1 and 753 mm on L2). The average daily air temperatures were 16.3 ◦C on L1 and 17.1 ◦C on L2, the average daily minimum air temperatures were 10.8 and 11.5 ◦C and the average daily maximum air temperatures were 21.8 and 23.5 ◦C, respectively. Rootstock M9 and the slender spindle training system were used in both orchards. In addition to cv. 'Majda', cv. 'Golden Delicious' was collected as a comparison due to its position in the European market. The leaves were incorporated in the study, to include another angle in comparison. They were sampled on 22 July 2019 at both locations. The leaves were ground in liquid nitrogen and lyophilized. The apples were harvested in their technological ripeness, as determined by firmness, the total soluble solids and starch test of cv. 'Golden Delicious' and cv. 'Majda' were harvested on 19 and 29 of September 2019, respectively. Both locations were harvested at the same time. Only apples of correct size (1st quality class) were collected and chosen for further handling and analysis. Approximately 30 kg of apples for each location and each cultivar were collected, half of which was immediately placed in cold storage and the rest were peeled, cut directly into liquid nitrogen and stored for the analysis of sugar, organic acid, phenolic content, and enzyme activity (POX and PPO). Apples were stored for 2 months in a cold storage with the temperature of 4 ◦C.
