Comparison of antifungal activity of extracts from different Juglans regia cultivars and juglone

This study discusses the similarities and differences between the antifungal activity of extracts from walnut green husks of Lake, Koszycki, UO1, UO2 and non-grafted cultivars as well as juglone against the plant pathogenic fungi such as Alternaria alternata, Rhizoctonia solani, Botrytis cinerea, Fusarium culmorum, Phytophthora infestans as well as Ascosphaera apis causing chalkbrood disease in honey bees. The obtained data show that the antifungal activities of the extracts do not always depend on the antifungal activity of juglone, and that they can be modulated by their other components. This fact allows us to conclude that juglone is not the only component of walnut green husk extracts which is responsible for the inhibition of mycelial growth. Phenolic compounds were found to be responsible for activity of the extracts and they can modify antifungal activity of juglone. •Walnut green husk extracts inhibit the growth of plant pathogenic fungi.•Extracts activity significantly exceeds the activity of juglone standard solutions.•Juglone is not the only component of the extracts responsible for the inhibition.•Phenolic compounds can modify the antifungal activity of juglone.