A Phytoalexin-Like Flavonol Involved in the Carnation (Dianthus caryophyllus)-Fusarium oxysporum f. sp. dianthi Pathosystem

The fungitoxic flavonol triglycoside, kaempferide 3‐O‐[2^G‐β‐d ‐glucopyranosyl]‐β‐rutinoside, is a constituent of the carnation cultivar ‘Novada’, known as one of the most resistant cultivar to Fusarium oxysporum f. sp. dianthi, causative agent of Fusarium wilt. Due to its constitutive presence within the carnation tissues, this antifungal flavonol should be considered as a phytoanticipin; its biosynthesis, however, is stimulated by the inoculation with F. oxysporum f. sp. dianthi, just as is the rule for a typical phytoalexin. The results seem to indicate that in carnation the concentration of some preformed antifungal flavonoids may be significantly increased by a fungal presence: owing to their fungitoxic properties, these molecules could cooperate, together with the unconstitutive and postinfectional anthranilic acid‐derivative phytoalexins, to the plant defensive response against Fusarium attacks.