EN
The content and composition of phenolic acids in leaves of two cultivars of large-fruited hazelnut with a differ level of resistance to aphids – filbert aphid and changes in their level caused by the pest feeding was studied. As a result of chromatographic analysis it was stated that the leaves of the tested cultivars showed the presence of eight phenolic acids: four, derivatives of benzoic acid (gallic, protocatechuic, p-hydroksybenzoic, salicylic acid) and four, derivatives of trans-cinnamon acid (chlorogenic, ferulic, caffeic and α-rezorcylid acid). Their concentration differed significantly between the studied cultivars. Only the control leaves of White Filbert cv. showed the presence of all eight phenolic acids, while the leaves infested by aphids did not contain ferulic and α-rezorcylid acids. The control leaves of Hall’s Giant cv. contained seven phenolic acids, except for the salicylic acid, which was found in the leaves infested by aphids. On the other hand, the infested leaves by aphids did not show the presence of ferulic acid. The leaves of White Filbert cv. were characterized by over twice higher content of phenolic acids as compared to the Hall’s Giant cv. Regardless of the cultivar, the dominant acids, in control leaves were caffeic acid and gallic acid. However, leaves infested by aphids contained higher amount of protocatechuic and caffeic acid. The high content of caffeic acid in the control leaves may suggest that their concentration determines resistance of hazel cultivar to herbivores.