Leaf phenolic content of pear cultivars resistant or susceptible to fire blight

Young leaf samples were taken from susceptible and resistant pear varieties in June and August for 2 years in 2000 and 2001 and were analyzed for phenolic compounds by using thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) after artificial inoculation with Erwinia amylovora. The distribution of spots in relation to phenolic compounds on TLC plates showed differences in resistant varieties compared to susceptible ones. The number of spots in resistant varieties was generally higher than the other group. Some spots were peculiar for distinguishing resistant and susceptible ones. Similarly, on HPLC dendograms, mean arbutin value was higher in the resistant group than the susceptibles both in 2000 and 2001. Additionally, arbutin content was found to be higher than chlorogenic acid content both in resistant and susceptible varieties.