Identification Of The Leaf Spot Pathogen On Chinese Yew And Screening Of Fungicides To Pestalotiopsis Microspora

Leaf blight is a common leaf disease of Taxus chinensis.It is difficult to prevent the occurrence of the disease,hence identification of the infecting species and study of biological characteristics are essential to control it.At present,the pathogen of the leaf disease of Taxus chinensis has not been clearly identified and the corresponding control technology also needs to be further developed.In this thesis,the main emphasis was to study the pathogen identification,biological characteristics and selection of control agents forb the leaf disease of Taxus chinensis,the principal results are as follows,1.Pathogen species identification of the leaf disease of Taxus chinensis in Fujian ProvinceSample of leaves infected with Taxus chinensis leaf blight in Fujian Province were collected,infected,isolated,cultured,and purified pathogenic bacteria as normal.The colonies of pathogens on the PDA medium were white,there were many cotton-like aerial hyphae on the surface,the acervalus was black,but not obvious.Conidiospores were fusiform,some were slightly curved,and were not obvious 5 cells in the 4 diaphragms area.The conidia size was 20.1?24.8x5.9?7.1?m.Three cells in the middle were stained,the first 2 dark brown and the third was stained light brown,the lengths of the stained cells are 13.0?16.5?m,there are mostly 2?3 colorless appendages on the caudal vesicle,sometimes there are 4,the top appendage is 8.3?16.5?m,there is a base appendage on the caudal vesicle,2.4 to 5.9?m.The taxus chinensis plant disease symptoms of the artificial inoculated one and the field natural one is the same.We re-isolate,cultivate and observe,and microscope inspect the pathogen form,it is showed that the re-isolated pathogen is completely the same with the inoculated one.In the rDNA-ITS section,we use the universal primers ITS1 and ITS4 to amplify the isolated pathogen genomic DNA,and nearly 800bp of amplified bands were obtained.The sequence alignment results showed that the third microspora ITS sequence similarity with the Pestalotiopsis microspora exceeded 99%.Base on the pathogen's morphological characteristics,pathogenicity identification,and the ITS sequence homology analysis result,it was identified as Pestalotiopsis microspora.2.The study of Pestalotiopsis microspora biological characteristicsThe pathogen causing leaf blight of taxus chinensis(Pestalotiopsis microspora)grew at 13?37?,the optimal growth temperature was 24?28?,and the mycelial growth was the best at 28 ?.The conidial germination temperature was 13?37?,and the optimal temperature was 28?.At temperatures below 13? or above 37?,germination was retarded or completely inhibited.The pathogen's mycelium grows well in the pH range of 4?12.Growth weak acidity pH 6.0-7.0 was optimal,7.5 is advised.The germination of conidia took place in the pH range of 4?12,at pH 6 the highest germination rate was observed,which shows that weak acidity is optimal for the germination.In the study of 5 carbon sources,sucrose and glucose can promoted the germination of conidia,while maltose,mannitol and lactose failed to promote the germination of conidia.Sucrose,glucose,maltose and mannitol markedly promoted the germination of conidia,with glucose exhibiting the optimal effect.In the study of 5 nitrogen sources,potassium nitrate was optimal for growth,while ammonium chloride,ammonium sulfate,sodium nitrate,ammonium nitrate and potassium nitrate significantly promoted the germination of conidia.Under all conditions of illumination,24 hours of all dark per day,24 hours of illumination per day,and 12hours of illumination and 12 hours of darkness,all could promote mycelial growth and germination of conidia.The lethal temperature for mycelium was 55?(10 min.),and the lethal temperature for conidium was 57?(10 min.)3.Indoor control agents selection for leaf disease of Taxus chinensisThe mycelial growth rate method was used to determine the growth inhibitory effects of 8 categories 11 kinds of fungicides on the mycelial growth of the pathogen causing leaf disease of Taxus chinensis.The results showed that 12 kinds of agents had different inhibitory effects,and the inhibitory effect of all of the agents increased with the concentration of each agent.The anti-bacterial effect of 12.5%Difenoconazole was the best,with an EC50 of 0.16mg/L,followed by BaiTai,25%Azoxystrobin suspension,25%Prochloraz emulsion,25%Iprodione suspension,and 25%Propionazole emulsion,with the EC50 being 0.875,1.43,1.45,1.48,and 2.4mg/L.The abovementioned agents can be used as the first choice for control of the leaf disease of Taxus chinensis.In this study,we identified the leaf disease pathogen of Taxus chinensis in Fujian Province by examining the morphological characteristics and utilizing molecular biology methods,and testing the biological characteristics and indoor agents toxicity of the pathogen,which provides a theoretical basis for the accurate diagnosis and effective control of the pathogen causing the leaf disease of Taxus chinensis.