Antifungal activity of plant essential oils and selected Pseudomonas strains against Phomopsis theicola

Abstract

Development of natural plant protection products as an alternative to synthetic fungicides is of significant importance regarding the environment. This study was carried out with an objective to investigate in vitro antifungal activities of several essential oils extracted from oregano, basil, myrtle and Turkish pickling herb, and the plant growth-promoting rhizobacteria in the genus Pseudomonas, against the phytopathogenic fungus Phomopsis theicola. Microdilution methods were used to determine the minimum inhibitory concentrations (MIC) of selected antimicrobial essential oils (EOs). All EOs exhibited significant levels of antifungal activity against the tested fungal isolates. The oregano EO was found the most potent one (MIC - 5.5 µg/mL), followed by basil (MIC - 75.0µg/mL), myrtle (MIC - 775 µg/mL) and Turkish pickling herb (MIC - 7750 µg/mL). Inhibition of Ph. theicola mycelial growth was observed for all tested Pseudomonas spp. strains. K113 and L1 strains were highly effective and achieved more than 60% of fungal growth inhibition using the overnight culture and more than 57% inhibition by applying cell-free supernatants of both strains. A future field trial with K113 and L1 cultures and cell-free supernatants, containing extracellular metabolites toward Ph. theicola, will estimate their effectiveness and applicability as an alternative to chemical protection of apple trees.

U novije vreme intezivno se radi na razvoju bioloških sredstava za zaštitu bilja, koja bi se uvodila kao zamena za sintetičke fungicide. U ovom radu ispitivan je in vitro antifungalni uticaj nekih etarskih ulja (EU) i odabranih rizobakterija koje stimulišu rast biljaka iz roda Pseudomonas na fitopatogenu gljivu Phomopsis theicola. Minimalne inhibitorne koncentracije (MIC) etarskih ulja su određene mikrodilucionom metodom. Sva primenjena EU su ispoljila značajni antifungalni efekat na ispitivani izolat gljive. EU origana je ispoljilo najnižu MIC od 5.5±0.51 µg/mL, zatim ulje bosiljka od 75.0±5.7 µg/mL, mirte 775±45.0 µg/mL i turske kisele biljke od 7750±4.5 µg/mL. Proučavan je stepen inhibicije porasta micelije Ph. theicola primenom različitih sojeva Pseudomonas spp. sojevi K113 i L1 su ispoljili visoku efikasnost inhibicije od preko 60% primenom dvadesetčetvoročasovnih kultura i preko 57% primenom filtrata supernatanta. U narednim ogledima u polju primenom kulture i supernatanta K113 i L1, koji sadrže ekstracelularne metabolite, proceniće se njihova efikasnost i mogućnost korišćenja kao alternative hemijskim sredstvima u zaštiti jabuke od Ph. theicola.