Olive (Olea europaea L.) fruits, fruit extracts and leaves are considered important sources of secondary metabolites. The main secondary metabolites in olive leaves are phenolic compounds, believed to have positive effects on health, as they have been proven to inhibit or slow down the growth of microorganisms. Pathogenic fungi infect plants and can threaten human health, thus inhibiting their growth is an important measure in ensuring food safety. Different fungicides are often used to control fungal growth, but due to their negative effects on the environment, natural agents with antifungal properties are being sought. The aim of the study was to evaluate the antifungal activity of the methanol extract from the leaves of olive (cv. Leccino) against plant pathogenic fungi Alternaria alternata, A. infectoria, Fusarium fujikuroi and F. oxysporum, which were previously isolated from the grains of common buckwheat (Fagopyrum esculentum Moench). By incubating fungi on PDA culture media supplied with different concentrations of methanol extract from olive leaves, the highest antifungal activity was found for A. infectoria and the lowest for A. alteranta. Methanol extract did not have a significant antifungal effect on the growth of F. fujikuroi and F. oxysporum. Foliar fertilization of olives with silicon and selenium increased the concentration of luteolin-4-glucoside in olive leaves, but not sufficiently for the methanol extract from olive leaves sprayed with Si+Se to inhibit the growth of selected fungi more than the methanol extract from unsprayed olive leaves.
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