Study On Pathogenic Mechanism Of Pestalotiopsis Guepinii To Camellia Pitardii

Cultivar Camellia pitardii of camellia, which have been grown in large scale in landscaping, and Pestalotiopsis guepinii (Desm.) Stey were selected as the research matierials in this experiment to study the natures of pathogenicity-related factors, toxin and cell wall-degrading enzymes(CWDEs) produced by P. guepinii. This study selected best culture conditions of toxin-producing of P. guepinii, and investigated the physical-chemical peculiarity of crude toxin, determined the types and activities and dynamic changes of CWDEs produced by P. guepinii in vivo or vitro, and studied the dynamics of CWDEs. In addition the pathogenesis of P. guepinii was studied by the effections of toxin and CWDEs to physiological and biochemical determination at leaves of Camellia pitardii. The results were as follows.1. P. guepinii could produce phytotoxin in fluid media. The conditions of toxin production of P. guepinii were optimized. Results showed the optimal liquid medium for producing toxin were Fries. The optimal cultural conditions for producing toxin were cultured period at temperature 25℃, medium initial pH 5.0, continuous light, shaking culturing,15d.2. Crude toxin of P. guepinii was preparated in the Fries medium and the optimal cultural conditions for producing toxin. The study showed that crude toxin was fairly heat resistant, but sensitive to pH. It had a poor tolerance against acid or alkali. When pH was 5.0, crude toxin had the most remarkable pathogenicity. Bioactive components of crude toxin were mostly larger polar substances.3. A series of CWDEs were found on P. guepinii in both camellia stem tissue and artificial culture. Among them, the activities of xylanase, pectin methyl-galacturonase (PMG),β-1,4- endo-glucanase(Cx) andβ-glucosidase were higher in both camellia stem tissue and artificial culture. The four CWDEs played important roles in pathogenesis. But activity of laccase was lower in both camellia stem tissue and artificial culture. Laccase showed little effect on pathogenesis.4. The studies on the kinetic charactristics of xylanase, PMG, Cx andβ-glucosidase showed that the optimal reaction temperature for PMG and Cx was 50℃, and for β-glucosidase and xylanase was 60℃. The optimal reaction pH for Cx,β-glucosidase and xylanase was 5.0, and for PMG was 5.0～6.0, indicating that the four enzymes prefer to the acid conditions. The activities of Cx, PMG and xylanase would decrease with the prolonging of reaction time, but the activity ofβ-glucosidase would rise sharply first and then decrease slowly. Maximum reaction speeds of the four CWDEs were in order of xylanase>PMG>β-glucosidase>Cx, and the affinities of CWDEs with substances were in order of PMG