PHENOLIC-COMPOUNDS OF APPLE AND THEIR RELATIONSHIP TO SCAB RESISTANCE

The contents of 15 different phenolic compounds in apple leaves and fr uit skin from various orchards were determined by HPLC. High concentra tions of flavan-3-ols were found in those orchards which were not infe cted by Venturia inaequalis. This observation corroborates earlier fin dings on different cultivars. The hypothesis that these compounds coul d be involved in the resistance of apple to scab was tested by inhibit ing the key enzyme of the phenol biosynthesis, the phenylalanine-ammon ia-lyase, in young shoots of the resistant genotype 'Sir Prize'. After inoculation of the inhibitor-treated leaves, severe symptoms of the d isease occurred. The fungal infection was confirmed by histological st udies. No flavonal-accumulation could be observed at the infection sit e which was the case in the non-inhibited but inoculated controls.