Effects of Green Husks of Hungarian-Bred Cultivars on Their Walnut Bacterial Blight Susceptivity

Abstract

The Persian walnut (Juglans regia L.) is one of Central Europe's most grown nut trees. In the green husks of walnuts, among the most important bioactive compounds are phenolics (hydroxybenzoic acids, hydroxycinnamic acids, flavonoids, naphthoquinones), which play an important role in the plant defense mechanisms against stress caused by various pathogens e.g., Xanthomonas arboricola pv. juglandis, furthermore mentioned as Xaj. The study examined the full Hungarian walnut assortment to detect the difference in phenolic profiles of their green husk and the relationship between the concentration of phenolic compounds, as well as their effects on tolerance against Xaj. All the phenological stages were recorded by Ctifl scheme. The phenolic compounds were determined by HPLC-DAD-ESI-QDA method, after which susceptibility test was carried out. The results show that concentration of the phenolic compounds varied by cultivars; it was higher in the locally-bred cultivars compared to ‘Chandler’, a more widespread cultivar. Phenolic compounds inhibited the artificial Xaj infection in the green husk. This effect had a strong correlation with the high phenols’ concentration, except for ‘Bonifác’. It is likely that the phenolics’ concentration in the walnut green husk has an important role in their defense against Xaj infection.