Seasonal Occurrence of an Antimicrobial Flavanone, Sakuranetin, Associated With Glands on Leaves of Ribes Nigrum

SUMMARY Sakuranetin, a flavanone aglycone, was present in glands on the adaxial surfaces of leaves of most varieties of Ribes nigrum L. These glands senesce early in the season, releasing their contents on to the surface of the leaf. Glands on the abaxial surfaces of leaves, which are different in structure from those of adaxial surfaces, do not contain sakuranetin. Conidia of Botrytis cinerea Pers. ex Fr. were inhibited from germinating on adaxial but not on abaxial surfaces of leaves at the time of adaxial gland senescence. Later in the season there was no inhibition of germination of conidia on either leaf surface. Because of the low activity of sakuranetin in vitro it was concluded that other factors were also likely to affect germination of conidia on adaxial leaf surfaces.