ANTIFUNGAL ACTIVITY OF FLAVONOIDS IN RELATION TO DEGREE OF HYDROXYLATION, METHOXYLATION AND GLYCOSIDATION

Antifungal effect of ten different flavonoids was tested against Alternaria tenuissima, Cladosporium cladosporioides, Spicellum roseum and Trichoderma hamatum in concns. 2 x 10^-4 (a) and 8 x 10^-4mol (b) on agar.
The unsubstituted flavone was the most active substance in concns. a and b.
In conc. b mycelial growth of A. tenuissima was inhibited to 61.2%, C. cladosporioids to 74.5%, S. roseum and T. hamatum to 100%. The corresponding flavanone was slightly less active with an average difference in inhibition rates of about 20%. 3- and 7-hydroxyflavone were almost ineffective.
Compared to naringin (4′,5,7-trihydroxyflavanone7-rhamnoglucoside) the corresponding aglycone – naringenin (4′,5,7-trihydroxyflavanone) – showed a substantial higher activity; e.g. in the case of T. hamatum the difference amounted to 60% at conc. b.
The same correlation was observed when hesperidin (3′,5,7-trihydroxy-4-methoxyflavanone7-rhamnoglucoside) and hesperetin (3′,5,7-trihydroxy-4-methoxyflavanone) were tested.
In general, 3,5,7-trihydroxyflavone (flavonol) showed a higher fungicidal activity than the 4′,5,7-trihydroxyflavone.

International Symposium on Natural Phenols in Plant Resistance

M. Weidenbörner, H.C. Jha

https://doi.org/10.17660/ActaHortic.1994.381.102