Lower crop load for Cv. Jonagold apples (Malus x domestica Borkh.) increases polyphenol content and fruit quality

The influence of crop load on fruit quality was investigated on 7-year-old slender spindle cv. Jonagold/M.9 apple trees. In mid June five different crop loads per tree were prepared by reducing the fruit number to average 30, 59, 104, 123, and 157 fruits per crown. The fruit from low-cropping trees had more red blush, a higher percentage of soluble solids in fruit flesh, and better flesh firmness in comparison to fruit from high-cropping trees. As the crop load decreased, the concentration of all phenolic compounds in the fruit samples (cortex plus skin) increased; concentrations of the most important individual fruit phenolics were also higher. When crop load fell from 157 to 30 fruits per crown, total polyphenols increased from an average of 1300 to 1680 mg/kg of fruit fresh weight (FW) (+29%), low molecular weight polyphenols increased from 1140 to 1570 mg/kg of FW (+38%), and high molecular weight polyphenols increased from 1740 to 2070 mg/kg of FW (+19%). The average increases in single polyphenols were even greater: chlorogenic acid (+82%); 4'-p-coumaroylquinic acid (+22%); catechin (+178%); and epicatechin (+71%). Ascorbic acid was not significantly dependent on crop load.