A. Lyubenova1, M. Nikolova2, S. B. Slavov1,3

1 AgroBioInstitute, Agricultural Academy, Sofia, Bulgaria
2 Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
3University of Forestry, Faculty of Agronomy, Department of Plant Protection, 10 Kliment Ohridski blvd., 1756 Sofia, Bulgaria

(Manuscript received 29 June 2022; accepted for publication 16 May 2023)

Abstract. The inhibitory potential of Greek oregano extracts, fractions and essential oil on three economically important plant pathogens on soybean was examined. In vitro experiments were conducted to determine the effects of essential oil (EO), acetone exudate (AE), methanol extract (ME), and its polar (PF) and non-polar (NPF) fractions, originating from O. vulgare ssp. hirtum plants, on the mycelial growth of Phytophthora sojae, Pythium debarianum, and Alternaria alternata, which were isolated from diseased soybean plants. Seven variants: EO, AE, ME, PF, NPF at concentrations of 100 mg/ml, blank (with the solvent – DMSO) and control (without treatment) were performed with all isolates. The mycelial growth of P. sojae was inhibited to the greatest extent – over 95% reduction of growth under the impact of EO, ME, AE and NPF. In A. alternata variant there was also a high degree of growth inhibition – most pronounced in EO variant (97%) and least in ME variant (78%). The weakest inhibitory effect of the studied extracts was observed in P. debarianum – between 27% (NPF) and 36% (ME). In polar fraction treatments, growth enhancement was observed in P. sojae and A. alternata. Oregano essential oil, methanol extract, acetone exudate and non-polar fraction can be considered as promising candidate active compounds of potential biopesticide formulations for the control of soybean diseases.