Inhibition of Ethanol Extracts of Psoralea corylifolia and Sophora flavescens on Phytophthora nicotianae and their Compound Effect

Phytophthora nicotianae is pathogen of tobacco black shank disease, leading to great economic losses each year. At present, controlling of tobacco black shank disease mainly depends on chemical fungicides, which may cause environmental and health problems. In this research, we carried out several experiments to investigate the effects of ethanol extracts from Psoralea corylifolia and Sophora flavescens on mycelial growth, sporangium and zoospore release of P. nicotianae, hoping to provide a new method for the control of tobacco black shank disease. The results showed that, extract of P. corylifolia and S. flavescens both showed good antifungal effects on P. nicotianae, with mycelial growth inhibition rates of 95.95% and 92.12% at 40 mg/mL and the EC50 values were 1.96 mg/mL and 6.37 mg/mL, respectively. The concentration of P. corylifolia extract completely inhibited sporangium production and zoospores release was 1.96 mg/mL and 0.98 mg/mL and the values of S. flavescens extract were 12.74 mg/mL and 6.37 mg/mL, which were much lower than 40 mg/mL. This phenomenon suggests that inhibitory effects of two plant extracts on P. nicotianae may mainly achieved by inhibiting sporangia production and zoospore release. The mycelium morphology was damaged in different degrees after treated by plant extracts, as extract of P. corylifolia led to wall rupture and mycelial adhesion, while extract of S. flavescens led to mycelial enlargement and distortion. The combinations showed better antifungal effect than single agent, which may be due to more diverse antifungal components in combinations. (C) 2020 Friends Science Publishers