Identification And Fungicide Screening In Laboratory Of Principal Fungus Of Bletilla Striata

Bletilla striata（Thunb.）Rchb.f.（Orchidaceae）is a traditional Chinese medicinal plant.In recent years,the demand for Bletilla striata has risen with the discovery of multiple medicinal functions of it.However,the frequently occurrence of various diseases that damage the yeild and quality of Bletilla striata has seriously affected the sustainable development of industry.In order to determine the pathogen in Bletilla striata and screen effective fungicides,typical leaf spot plant samples were collected and the fungal pathogens were isolated and purified for this study.Pathogenicity analysis were carried out according to Koch’s rule,and the pathogens were characterized by morphological characteristics and multi-gene sequences.The inhibition of fungicides on the representative strains were determined by mycelial growth rate method on PDA plate.The main results as following:1.Diseases investigation and the fungus identification in Bletilla striata.The main diseases of Bletilla striata in the survey area are leaf spot diseases and anthracnose,which are serious.Pathogens of Bletilla striata were isolated and purificated for pathogenicity test,results indicated that BJ19.4.1,BJ19.4.2,BJ106.4,BJ25.4,BJ26.3,BJ28.1,BJ111.1,BJ111.4caused leaf spot disease.Brown colonies and catenate or solitary conidian of BJ19.4.1,BJ19.4.2,BJ106.4 were observed in plate,these strains were determined as Alternaria alternata based on morphological characteristics and ITS,SSU,LSU,TEF1,GAPDH,RPB2 analysis;BJ25.4,BJ26.3,BJ28.1 with white and irregular colonies,elongated and curved conidiophores,hyaline and cylindrical conidiogenous,were identified as Diaphorthe sackyae,D.phaseolorum and D.ceridiyae respectively according to morphological characteristics and ITS,CAL,HIS3,TUB2,TEF1 sequence analysis.As D.sackyae and D.ceridiyae were novel species without described.BJ111.1 and BJ111.4 were determined as Neofusicoccum parvum based on similar morphological characteristics and consistent ITS,TEF1,TUB2 sequences.By combining ITS,ACT,CHS-1,HIS3,GAPDH,TUB2 sequence analysis,BJ103.2,the pathogen of Anthracnose,were identified as Colletotrichum orchidophilum with grey colonies,straight conidian.2.Pathogen fungicide screening in the laboratory for Bletilla striata.Results of indoor virulence test of the fungicide showed that the 75%trifloxystrobin and tebuconazole water dispersible granule（NATIVO,75%WP）have the best effective on C.orchidophilum,D.phaseolorum and A.alternata on PDA,and EC₅₀ values were 7.92μg/m L,0.25μg/m L and1.25μg/m L respectively.0.01μg/m L NATIVO was effective in suppressing the mycelial growth of D.phaseolorum in PDA plate,71.7μg/m L NATIVO could suppress the growth of C.orchidophilum completely,and the inhibition rate of A.alternata was 83%when 100μg/m L NATIVO was used.Carbendazim is a highly effective fungicide for N.parvum(EC₅₀=0.02μg/m L),which can inhibit the growth of pathogenic bacteria completely at 0.1μg/m L.The results of this study provided theoretical basis for the pathogen determination and control of Bletilla striata leaf spot and Anthracnose,which is of great significance for guiding agricultural production of Bletilla striata.