Primary antibacterial mechanism of ethanol extract of Scutellaria baicalensis against the pathogens of kiwifruit canker

【Objective】To explore the antibacterial mechanism of ethanol extract of Scutellaria baicalensis(ESB) on the pathogen of kiwifruit canker against Pseudomonas syringae pv. actinidiae(Psa) and to provide a theoretical foundation for the development of new plant-derived fungicides.【Method】The sensitivity of Psa to ESB was evaluated by the agar punch method. The minimum inhibitory concentration(MIC) and the minimum bactericidal concentration(MBC) were determined by gradient dilution method in liquid medium. The effect of ESB on Psa at 1/4 MIC,1/2 MIC,3/4 MIC and MIC was determined. Growth curre was drawn by monitored optical density of the bacterial cullture. Electric conductivity of culture supernatant was measured by conductivity meter. Extracellular soluble protein content was determined by the Coomassie brilliant blue method. Alkaline phosphatase(AKP) activity was measured with an AKP kit.Phosphorus metabolism was detected by the ferrous sulfate method. Respiratory chain dehydrogenase activity was detected by oxidationreduction reaction. Swimming motility ability was detected in 0.3% solid medium. Scanning electron microscope(SEM) and transmission electron microscope(TEM) were performed to observe Psa morphology at MIC.【Result】The inhibition zone diameter of ESB against Psa was above 16.00 mm. The MIC and MBC were 2.4 mg/mL. ESB inhibited the growth of Psa,damaged the cell membrane and cell wall which caused the leakage of proteins and electrolytes. Moreover,the ESB interfered with normal material and energy metabolism. ESB can significantly resist the swimming of Psa and hinder cell migration. ESB can significantly resist the swimming of Psa and hinder cell migration. Scanning electron microscopy and transmission electron microscopy showed that morphology of Psa was shortened,depressed,deformed and lysed with ESB,which caused the leak of cytoplasm and bacterial lysis.【Conclusion】ESB inhibit the normal growth of Psa by destroying the structure of Psa and interfering with substances and energy metabolism. ESB has the potential to be developed as a plant-derived fungicide.