Inhibition Mechanism Of I.Britannica L. Effective Elmemt To Phytophthora Capsici

Preliminary study showed that the mycelium growth of Phytophthora capsici was inhibited by 1,6-O, O-diacetybritannilactone (DABL) which was isolated from the inflorescence of Inula britannica L. In oeder to locate the mechanism, a series of research was conducted. Effect of different physiological stage of Phytophthora capsici was studied in vitro. Effect of mycelial morphology and ultrastructure was observed by optical microscopy, scanning electron microscopy and transmission electron micrographs. Change of electrical conductivity and malondialdehyde content was determined. Mycelium protein and sugar content were tested. The major findings were listed as follows:Mycelial growth was inhibited with increasing concentration in the range of 0.05 mg/mL to 1 mg/mL. The inhibition rate was 83.18% at the concentration of 1 mg/mL. The EC50 value was 0.087 mg/mL and the toxic regression equation is Y=6.015+0.9582X (r=0.9802). Sporangium generation was inhibited significantly with increasing concentration range of 1μg/mL (29.32%) to 5μg/mL (80.53%). Sporangium was absolutely inhibited at the concentration of 25μg/mL. The toxic regression equation was Y=4.1854+2.1106X (r=0.9640). The release of zoospore treated with DABL was not significantly inhibited within the tested concentration range.Microscopic observation found that the fungi branch increased and the end of the branch inflated, mycelium stretch severely affected after dealt with DABL. Scanning electron microscopy results showed that the mycelial growth was messy when cultered in poisonous medium for 3 d. The mycelium was dry and collapsed. Some growing point shriveled, some swelled, the top of the growing point blunt round, the space between mycelium septum was shortened. Cultured for 5 d, water shortage made the mycelium dead-like, the mycelium curled and collapsed more serious, the growing point shriveled and deformed. Observed by transmission electron microscopy, the nucleus, mitochondria, endoplasmic reticulum and other organelles uniformly distributed in the cytoplasm of untreated cells and kept their structure complete. Cultured in poisonous medium for 3 d, a large number of inclusions and vacuoles produced in mycelium cells and extravasation around mycelium cells, the color of the organelles deepened. Cultured for 5 d, vacuolization phenomenon was more serious, the organelles color further deepened, some cells turned to cavity cells, cytoplasm distributed asymmetrically.Increase of electrolytes permeability, measured by change of electrical conductivity of medium of Phytophthora capsici, was found upon treatment with DABL. MDA content was higher when treated with DABL, which demonstrated that cell membrane was destroyed by lipid peroxidation.Soluble protein test showed that DABL inhibited the synthesis of soluble protein. Reducing sugar test showed that reducing sugar content in mycelial treated with DABL increased. Presumably, DABL may improve cellulase activity, cell wall may be degraded. Soluble sugar test showed that soluble sugar content increased in the mycelium diaposed with DABL, metabolism consuming soluble sugar decreased, so that the soluble sugar accumulated.