Croatian traditional apple cultivars: why are they more resistant to plant diseases?

Polyphenols are molecules with strong biological activity, which are the bearers of apple resistance to plant diseases, as well as to abiotic stress from various sources. Moreover, it has been shown that apple cultivars with higher content of polyphenols are more resistant to plant diseases. Some of the biological activities of polyphenols are antiphlogistic, antimutagenic and antioxidant activity. In addition to the above, some polyphenols such as chlorogenic acid, phloridzin and quercetin showed potent antimicrobial and antifungal activities by targeting intracellular processes in microorganisms or inducing irreversible permeability changes in cell membrane. Based on that, this study aimed to detect, quantify, and compare the amounts of chlorogenic acid, phloridzin, and quercetin in ten Croatian traditional and five conventional apple cultivars by high- performance liquid chromatography with diode- array detector. Total phenolic acids, dihydrochalcones and flavonols were also determined. The results showed that Croatian traditional apple cultivars had significantly higher amounts of the investigated compounds compared to conventional apple cultivars. The highest amount of chlorogenic acid (30.29 ± 0.34 mg/100 g DW), phloridzin (3.12 ± 0.01 mg/100 g DW) and quercetin (11.68 ± 0.09 mg/100 g DW) had ‘Božičnica’, ‘Mašanka’ and ‘Petrovnjača’, respectively. The highest contents of the total phenolic acids, dihydrochalcones and flavonols were detected in ‘Božićnica’ (31,94 ± 0.65 mg/100 g DW), ‘Mašanka’ (3,52 ± 0,52 mg/100 g DW) and ‘Fuji’ (19.11 ± 0,56 mg/100 g DW), respectively. The main flavonol detected in ‘Fuji’ was quercetin-3-rutinoside. These results present the beginning of the research on the resistance of Croatian traditional apple cultivars to plant diseases funded by the Croatian Science Foundation (UIP-2020-02-8461).