Antifungal activity of carnosic acid and carnosol against phytopathogenic fungi.

Intoduction : At present the use of chemical pesticides, including fungicides, is not fully accepted by end consumers because of potential risks of chemical residues in fresh foods and foodstuff . Several evidences support that chemical substances produced by the secondary metabolism of plants has evolved to protect them from attack by pest and disease. At this regard research into plant secondary metabolites with anti-fungal activity is now intensifi ed due to the enormous potential to inspire and infl uence research in developing modern agrochemicals, hopefully characterized by low environmental persistence. Since phenolic diterpenes of the carnosic acid oxidation cascade showed antimicrobial activity [1], the antifungal activity of carnosic acid (CA) and carnosol (CAR) was investigated. Methods: e antifungal activity against some phytopathogenic fungi (Colletotrichum coccodes, Fusarium oxysporum f. sp. cyclaminis, Sclerotinia sclerotiorum, Botrytis cinerea, Rhizoctonia sp. AG-A) was investigated by comparison with four standard classical fungicides, using the poisoned food technique. CA and CAR were tested at various concentrations: 5, 10, 50, 250, 500, 750, and 1000 mg/mL. e concentrations of the fungicides were those recommended by the manufacturers: Bavistin FL (BASF) (carbendazim 41%), 500 mg/mL; Rovral FL (BASF) (iprodion 25%), 675 mg/mL; Ortiva (Syngenta) (azoxystrobin 23%), 250 mg/mL; Switch (Syngenta) (ciprodinil 37% and fl udioxonil 25%), 375 and 250 mg/mL respectively. After 5 days of incubation in the dark at 25°C, mycelium growth of selected fungi inoculated in poisoned solid substrate (Potato Destrose Agar) was assessed in order to defi ne MIC and EC50. Results an discussion: Against C. coccodes MIC threshold was 500 and 1000 mg/mL respectively for CA and CAR. Against F. cyclaminis it was possible establish the EC50 respectively for CA and CAR at 30 mg/mL and at 40 mg/mL, against S. sclerotiorum at 35 mg/mL and at 1000 mg/mL, against B. cinerea at 50 mg/mL and at 200 mg/mL. Against Rhizoctonia sp. it was possible defi ne the MIC for CA at 500 mg/mL and the EC50 for CAR higher than 1000 mg/mL. CA and CAR were, at the same concentrations, more eff ective than Bavistin, Rovral and Ortiva on C. coccodes. e activity of CA was similar to that of Switch on C. coccodes and Rhizoctonia sp.. CA and CAR are natural antioxidants of commercial interest to the food industry. From our results carnosic acid and carnosol may be considered as potential antifungal compounds with an expected low environmental toxicity. Furthermore since low quantities of carnosic acid and carnosol used as antioxidant food additives are not of safety concern [2] and these compounds are utilized as food supplements, the possible presence of traces of these substances on edible plant material after phytoiatric application would not represent a toxicological concern. References [1] S. Weckesser, K. Engel; B Simon-Haarhaus; A. Wittmer; K. Pelz; C.M. Schempp Phytomedicine 2007,14, pag. 508-16; [2] e EFSA Journal 2008, 721, 1-3.