| Black walnut Cytospora Canker is a newly disease,which occurred in Chabchal county,Xinjiang,China.The disease mainly impacts black walnut branches and stems,and leads to dieback of parts of the tree.Black lesions appear on the epidermis of diseased branches,and the phloem of diseased branches turns black and brown,which can extends to the xylem,which caused part branches to drain and the tree body to die.This disease has never been reported in black walnuts in China.Based on this,ccurately identified pathogens of black walnut rot,systematically studied its main biological characteristics,and screened the efficient fungicides.The results are as follows:(1)The suspected pathogens were accurately identified using pathogenicity tests,morphological and molecular techniques.The pathogenicity test of five strains were carried out on health host plants,which can cause the same symptom as the field.After the diseased tissues were separated again,the morphological of isolated strains is same as the original strains while no symptoms were detected on blank control branches.It demonstrates that the inoculated strain was the pathogen of black walnut Cytospora canker.Basing on the comprehensive comparison of morphological characteristics using"Fungal identification manual"and reference,the pathogen of the disease was similar as C.chysosperma.Partial sequences of transcription elongation factor(EF1a),microtubule gene(TUB2)and ribosomal DNA gene(ITS)were obtained by PCR amplification.Through the analysis of genetic and evolutionary relationship,the base sequences of the three genes had the highest similarity to the corresponding base sequences of C.chrysosperma and were clustered into the same group.Finally,the pathogen of black walnut Cytospora canker was identified as C.chrysosperma.(2)Preliminary studies on the main biological characteristics of C.chrysosperma isolated from black walnut putrefying disease showed that:pathogens could grow on 8 kinds of different carbon source media,but they grew better on PDA,PSA,PCA and carrot medium than on other 4 different carbon source media.Pathogens grew best on PDA,followed by PSA,PCA and carrot culture.Pathogens could grow at 5-35℃,and the optimum temperature was 25℃.Pathogens could gow at pH 3-10 and the optimal pH value was 5.The mycelial growth of pathogen was not significantly difference under 24 h light,12 h alternation of light and dark and 24 h darkness.(3)The toxicity test of 12 kinds of fungicides to black walnut Cytospora Canker was showed that the selected fungicides to the pathogen of black walnut Cytospora Canker have existed obvious differences.Among them,10%Difenoconazole WG was the most virulent,EC50 value was 0.001 mg/L,followed by 16%Mixture of difenoconazole and zhongshengmycin WP,EC50 value was 0.017 mg/L,while 47%kasugamycin-copper acetate WP was the least virulent,EC50 value was 2481.10 mg/L.It was showed that the selected 12 kinds of fungicides have certain inhibitory effects on mycelial growth,among them,the 10%Difenoconazole WG has the strongest inhibitory effect,followed by 16%Mixture of difenoconazole and zhongshengmycin WP.The field efficacy test of the test agent on black walnut showed that the control effect of different fungicides on black walnut was different in field.Among them,the control effect of 16%Mixture of difenoconazole and zhongshengmycin and 10%Difenoconazole was 84.26%and 75.13%respectively,which showed better control effect on black walnut.Therefore,16%Mixture of difenoconazole and zhongshengmycin and 10%Difenoconazole can be used as alternative fungicides to control black walnut in the field. |
PDF Full Text Request