| Cucumber target leaf spot caused by Corynespora cassiicola is one of the most important epidemic diseases in cucumber production in recent years,which had caused a large area reduction of cucumber production.Finding effective prevention and control measures is the main task to promote the sustainable development of the current cucumber planting industry.Currently,it is mainly controlled by chemical methods,however,the pathogen is easy to mutation and long-term use of chemical reagents such as fungicides can lead to pathogenic fungi develop resistance,trigger food safety and environmental issues.So agricultural production urgently need low toxic,harmless and environmentally friendly biological control methods.Actinomycetes are a kind of microorganisms with wide distribution,variety and strong functions.Therefore,it is often used for biological control in recent years.In this study,the rhizosphere soil of cucumber and companion wheat was used to isolate actinomycetes and separated by various media.Strain Streptomyces NEAU-J2 with good activity was screened by inhibiting Corynespora cassiicola and other phytopathogenic fungi and bacterial activity tests.The control effect of NEAU-J2 on cucumber target leaf spot disease was studied by vitro leaf test,pot experiment.The secondary metabolite of NEAU-J2 was also separated.Meanwhile,one new active actinomycete were studied by polyphasic taxonomy method.The main results of this study are as follows:(1)We isolated 262 actinomycetes by 5 isolation culture medium(GS、HV、AAG、CPA、DPA),119 were isolated from the rhizosphere soil of cucumber,and the remaining 143 were isolated from the rhizosphere soil of the companion wheat.(2)After screening inhibition of the activity to Corynespora cassiicola,32 out of 262 actinomycetes inhibition rate were more than 20%,and the inhibition rate of 16 strains reached more than 40%.The 10 strains of actinomycetes with the best antibacterial activity were selected for broad-spectrum antibacterial activity,and the strain NEAU-J2 was found to have a better broad spectrum of antibacterial activity.(3)In vitro leaves and pot experiments showed that the control effects of cucumber target leaf spot disease were very good after treatment with NEAU-J2 spore suspension and fermentation broth,respectively.The fermentation broth had a better prevention effect,and the control effects of vitro leaves and pot experiments were 81.2% and 82.1%,respectively.(4)By culture characterization analyzing,the culture characteristics of strain NEAU-J2 were consistent with Streptomyces,and it was preliminarily determined that the strain NEAU-J2 belong to the genus Streptomyces.Otherwise,the functional characterization showed that the inhibition effect of NEAU-J2 fermentation broth on Corynespora cassiicola had a good UV stability.And the strain NEAU-J2 can produce chitinase,the transparent ring diameter was 16.2 mm per colony.(5)By isolating the secondary metabolites of the strain NEAU-J2,we initially isolated three reported compounds,they were 17-O-demethyl-geldanamycin,pteridic acid and pteridic acid F.When the concentration of pteridic acid hydrate was 5 mg/m L,the inhibiti rate of pteridic acid hydrate was 56.3%.(6)In this experiment,one new strain of actinomycetes was identified by sequence analysis of 10 strains with the best inhibition rate of Corynespora cassiicola.The strain was studied by polyphasic taxonomic investigation at molecular level,morphological level,chemical classification level and whole genome sequence analysis,and named it Streptomyces inhibens. |
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