Screening,Identification And Optimization Of Fermentation Conditions Of An Antagonistic Actinomycete To Cucumber Fusarium Wilt And Research On Its Biological Characteristics

Cucumber is a worldwide vegetable and it is popular.China's has the planting area and production of cucumber in the world and cucumber is a major cash crop.In recent years,cucumber wilt disease has become more and more serious because of the high-density planting and improper management of cucumber planting areas,which has led to the serious spread of soil-borne diseases.Cucumber Fusarium wilt is a serious soil-borne fungal disease caused by Fusarium oxysporum f.sp.cucumerinum.It occurs in planting areas and seriously restricts the development of cucumber industry at home and abroad.At present,the control of cucumber Fusarium wilt mainly includes agricultural control and chemical control.Due to the high cost of agricultural control and environmental pollution caused by chemical control,it is urgent to study environmental friendly prevention and treatment methods.Biological control has this characteristics and it is what we need.This research collected soils samples from the Hexi Corridor,Screening and identification antagonistic actinomycete strains has strongly inhibitory activity against Fusarium oxysporum f.sp.Cucumerinum.Moreover,we explored its biological characteristics and optimal fermentation formula and fermentation conditions.The growth promoting strain was screened in this antagonistic actinomycetes,and screening and plant growth promoting strains has significantly promoted cucumber plants growth.The main results list follows:1.The method of dilution plate coating was applied to isolated 168 actinomycete strains from the Hexi Corridor.2.The methods of growth plate-confrontation was applied to first screening antagonistic actinomycetes and 14 strains has the strongly inhibitory activity against Fusarium oxysporum f.sp.Cucumerinum,which calculated as 8.33%.3.The methods of speed rate were applied to second screen antagonistic actinomycetes and combined with first screening results to determine strain 16-3-10as antagonistic actinomycete.4.Themorphologicalcharacteristics,physiologicalandbiochemical characteristics,and 16S rRNA gene sequence of strongly antagonistic actinomycete strain 16-3-10 can be classified as Streptomyces sp..5.To explore the biological characteristics of strain 16-3-10,the antagonistic strain has a broad antibacterial spectrum,strong tolerance to saline-alkali environment,and the ability of plant growth promoting.6.The culture conditions of strain 16-3-10 were optimized with a medium was as follows:Millet 10.0 g/L,lactose 20.0 g/L,peptone 1.0 g/L,NaCl 5.0 g/L,CaCO₃ 6.0g/L at 28?,liquid volume 50 mL in 250 mL flask,initial pH of 10.0 for 3 d,and inhibition rate of strain 16-3-10 to pathogen reached to 82.50%under this condition.7.The fermentation extracts of strain 16-3-10 had high inhibitory activities on Fusarium oxysporum,Alternaria solani,Fusarium solani,Rhizoctonia solani and Valsa mali.Its antifungal activities were almost not affected under pH range of 4⁹,100?for 1 h,UV irradiation for 24 h and 4?for 60 d.8.9 strains with plant growth promoting bacteria were screened from antagonistic actinomycetes.Strain 4-2-1 and 4-3-6 has the ability of plant growth promoting.9.The results of cucumber plant growth promotion test indicated that the root length,fresh weight,dry weight and number of leaves increased respectively.The morphological characteristics,physiological and biochemical characteristics,and 16S rRNA gene sequence of strongly antagonistic actinomycete strain 4-2-1 can be classified as Streptomyces sp..