Propolis extract combined with oregano essential oil applied to lima bean seeds against Sclerotinia sclerotiorum

Abstract

In this study, propolis extract (EPE) and oregano essential oil (OEO), both natural products with different bioactive compounds, were evaluated in vitro and in vivo against Sclerotinia sclerotiorum. This phytopathogen is important worldwide as it can contaminate seeds and infect seedlings of many species. Antifungal susceptibility assays on culture media revealed that EPE and OEO were highly active against this phytopathogen, both individually and combined. EPE showed a fungistatic dose-dependent effect, acting mainly through diffusion, while OEO completely prevented mycelial growth at very low concentrations, with a combination of vapor and diffusion activity. Interestingly, OEO was more effective than EPE, as their minimum inhibitory concentrations were 0.39 μl/mL and 5 μl/mL, respectively. Combinations of EPE and OEO showed, depending on the doses, additive or synergistic antifungal effects. In the in vivo trial, dilutions of EPE and OEO made in sterile distilled water (SDW) were tested through a pathosystem with lima bean seeds and S. sclerotiorum. Seeds soaked in formulations with 40% EPE + 12% OEO + 48% SDW, and 20% EPE + 6% OEO + 74% SDW reduced disease incidence of 40% and 60% respectively, significantly decreased severity, with a minimum phytotoxic effect. This study strengthens previous work showing the antifungal action of EPE and OEO against S. sclerotiorum, and, as a main goal, highlights their potential for the development of biofungicides to protect lima bean seeds.