Isolation And Identification Of Stem And Leaf Blight Of Peucedanum Praeruptorum And Screening Of Effective Prevention Agents

Stem leaf blight caused by Rhizoctonia solani is one of the important diseases of ningqianhu.This experiment collected the plants in the plant base of Ningguo,Anhui Province,and isolated one strain from the infected ningqianhu.Through the morphological observation,molecular biological identification,biological characteristics and indoor drug screening,the pathogen R Solani was suitable for growth environment and the control effect of six fungicides on pathogens was determined.On the basis of single agent,four kinds of agents with better control effect and lower cost were selected.The compound was carried out according to different proportion,which provided reference for the occurrence,prevalence and prevention of stem and leaf blight of ningqianhu.The main results are as follows:1 Isolation and identification of pathogenic bacteriaThe pathogen was purified by tissue isolation method.Under the microscope,the hyphae of the pathogen on potato glucose agar medium（PDA）were white at the initial stage,sparse,radiating and expanding to the surrounding.The shape of the hyphae was round and regular.The hyphae branched near right angles,and the branches constricted obviously and there was a diaphragm not far away.The color of the hyphae changed from light brown to black brown at the late growth stage The number of mycelial aggregates increased.The growth rate of the strain was fast,and the mycelium grew over the culture dish with a diameter of 90 mm in 2-3 days.After 10 days,sclerotia was formed,which was nearly round or irregular in shape,with brown to dark brown color and rough surface.The mycelial cells are multinucleated and each cell has three or more nuclei.The phylogenetic tree showed that the pathogen and Rhizoctonia solani were in the same branch,and the support rate was 100%.2 Biological characteristics of Rhizoctonia solani from Peucedanum ningenseThe optimum medium,carbon source,nitrogen source,temperature,p H value,light condition and lethal temperature of Rhizoctonia solani were determined.The results showed that the most suitable medium for the growth of Rhizoctonia solani was plate counting agar medium（PCA）and potato glucose agar medium（PDA）.The growth effect of the pathogen was the best at 30℃,and the most suitable temperature was 25℃to 30℃The mycelia grew best in the medium with glucose as carbon source and yeast powder as nitrogen source.The mycelia grew fastest under the condition of total dark light.The lethal temperature of mycelia was 47℃.3 Toxicity of six chemical fungicides to Rhizoctonia solaniThe indoor toxicity of Difenoconazole,pyrazoxystrobin,tebuconazole,azoxystrobin,pichiamide and tifuramide to Rhizoctonia solani was determined by growth rate method.Seven concentration gradients were set for each drug,and sterile water was used as control.The drug containing plate was prepared according to the ratio of 1:9.The results showed that:all the six fungicides had control effect on the pathogen,among which the biological activity of tifuramide was the most significant,the effective medium concentration EC₅₀was 0.0729±0.00364μg/m L,followed by pyrazoxystrobin,the average EC₅₀was0.1036±0.00518μg/m L,the biological activity of azoxystrobin was not significant,the average EC₅₀was 1.5683±0.04704μg/m L.The EC₅₀of difenoconazole,tebuconazole and pichiamide were 0.2225±0.00852μg/m L,0.1134±0.00567μg/m L and 0.5567±0.00895μg/m L,respectively.The order of sensitivity of the six fungicides was as follows:cefuroxime(EC₅₀:0.0729±0.00364μg/m L)>pyrazoxystrobin(EC₅₀:0.1036±0.00518μg/m L)>tebuconazole(EC₅₀:0.1134±0.00567μg/m L)>Difenoconazole(EC₅₀:0.2225±0.00852μg/m L)>pichiamide(EC₅₀:0.5567±0.00895μg/m L)>azoxystrobin(EC₅₀:1.5683±0.04704μg/m L).4 Chemical compositionDifenoconazole,pyraclostrobin,tebuconazole and tifuramide were compounded in different proportions.The results showed that only 1:9 of Difenoconazole and tifuramide was synergistic,1:9-7:3 of tifuramide and pyraclostrobin was synergistic,8:2 was additive,9:1 was antagonistic,and 1:9,2:8,3:7 of tifuramide and tebuconazole was additive.