Identification Pathogen Causing Leaf Blight Of Phoebe Zhennan And Its Physiological And Biochemical Effects On Leaves And Fungicide Screening

Phoebe zhennan is the level of protection of plant in China.It's not only a good timber species,but also a good tree species in the landscape.Recent years,the symptoms of suspected leaf blight was found in Phoebe zhennan planted in Sichuan Agricultural Uniersity in Wenjiang District.It's a serious impact on the growth of Phoebe zhennan,but also on it's ornamental value,if paid not enough attention,it will cause economic losses.In the study,collecting leaf blight samples from Sichuan Agricultural Uniersity,studying the biological characteristics of the pathogenic bacteria and biochemical effects on leaves,doing indoor chemical designation test,in order to learn about the disease and provide a theoretical basis for the prevention of leaf blight,the results are as follows:1?Using the method of normal tissue separation,1 separation was isolated from leaf sample,the pathogenicity of separation was verified according to Koch's Postulates.The result showed that the symptoms was consistented with Phoebe zhennan planted in school.According to the identification of state characteristics and r NDA-ITS sequence analysis,the result showed that the pathogenic bacteria is Deuteromycetes,Moniliales,Dematiaceae,Alternaria tenuissima(Fr.).2?The effects of culture medium,carbon resources,nitrogen resources,p H,temperature and illumination on the growth of pathogenic bacteria.The experimental results showed that:(1)the pathogen growth in PDA culture medium was the best,followed by PSA medium;(2)the best carbon resources for the growth of pathogen is sorbitol,followed by soluble starch;(3)the best nitrogen resources for Alternaria tenuissima(Fr.)is organic nitrogen resources peptone and beef extract,ammonium salt has inhibitory effect on pathogen growth;(4)the pathogen could grow in p H5-9 and the best p H value was 5.8;(5)the pathogen can could grow in 10-35?,the best temperature was 25?;(6)alternating light and dark conditions is the most conducive to the growth of pathogen.3 ? Inoculating Alternaria tenuissima(Fr.)on healthy leaves,gaguing the content of malondialdehyde(MDA)and the activity of catalase(CAT)and peroxidase(POD)continuously.The results show that the infection of Alternaria tenuissima.caused(MDA)content increased,catalase(CAT)and peroxidase(POD)activity was lower than that of the control.4?Indoor chemical designation test results indicated that 7 kinds of fungicides virulence of the order of 50%Prochloraz>50%Carbendazim>12.5%Diethofencarb>70%Thiophanate-Methyl>50%Procymidone>70%Mancozeb >50%Inprodione.The best effect of fungicides is 50%Prochloraz,the EC50 value is 0.3157mg/L.The worst effect of fungicides is 50% Inprodione,the EC50 value is 18.4064mg/L.5?The results of the study provide a theoretical basis for the prevention and treatment of leaf blight of Phoebe zhennan:the best effect of fungicides is 50% Prochloraz.Avoiding using organic fertilizer and using ammonia fertilizer as a synergist to improve the effect of chemicals.In the daily maintenance,we should keep the rational planting density,pruning the disease branches in time,and keep good ventilation,which can reduce the occurrence of the disease.