POLYPHENOL CONTENT IN APPLE FRUITS AS AFFECTED BY CROP LOAD AND RATE OF APPLIED NITROGEN

The influence of crop load and N rates on polyphenol content in fruits of ‘Fuji’, ‘Gala’ and ‘Golden Delicious’ apple was investigated. Trees were grafted on M9 rootstock, grown at a spacing of 2.8 x 0.7 m and trained to slender spindle. Nitrogen was ground-applied at three rates (60, 90 and 120 kg N ha^-1). In mid June, different crop loads were established by adjusting fruit number to three levels for ‘Fuji’ (5.0, 3.5 and 1.5 fruits cm^-2 TCSA) and ‘Gala’ (9.0, 6.0 and 3.0 fruits cm^-2 TCSA), and two levels for ‘Golden Delicious’ (4.0 and 1.5 fruits cm^-2 TCSA). According to fruit analyses results (cortex plus skin), total polyphenols content in ‘Golden Delicious’ were between 147-197 mg kg^-1, in ‘Gala’ between 132-205 mg kg^-1, and 144-178 mg kg^-1 of fresh fruit weight in ‘Fuji’. The influence of applied N fertilizer or crop load on fruit polyphenol content was not consistent, and no significant differences were found. Results indicate that, crop load or N fertilizer do not represent major regulatory factors in polyphenols formation in apples.