The in vitro antifungal evaluation of a commercial extract of Chilean propolis against six fungi of agricultural importance
Propolis has been used for millennia for its antimicrobial and pharmaceutical properties, whereas its use as an agricultural antifungal agent has only recently been assessed. The chemical characteristics of six ethanolic extracts of Chilean propolis (EEP-1 to EEP-6) were evaluated. The total polyphenols ranged between 7.8 and 42.3 mg mL-1 equivalents of a 2:1 pinocembrin: galangin standard, and the total flavonoid contents ranged between 4.0 and 19.7 mg mL-1 equivalents of quercetin. A high-performance liquid chromatographic (HPLC) analysis allowed the identification of caffeic acid, myricetin, quercetin, kaempferol, apigenin, pinocembrin, galangin, caffeic acid phenethyl ester (CAPE) and rutin. The EEP-3 extract was selected for additional studies based on the higher total polyphenols and flavonoids contents (42.3 and 19.7 mg mL-1, respectively). The antifungal effects of four different concentrations (0.5, 1.0, 2.5 and 5.0 %) of EEP-3 on Alternaria alternata, Fusarium sp., Ulocladium sp., Botrytis cinerea, Penicillium expansum and Trichoderma reesei were evaluated in vitro using the agar dilution method. Although significant differences occurred among the extract concentrations, the results indicated that EEP-3 inhibited the mycelial growth of the six fungi evaluated.