Identification And Biocontrol Effect Of Antagonistic Actinomyces Strain CT205 Against Fusarium Wilt Of Cucumber

Cucumber wilt disease, caused by F. oxysporum f. sp. cucumerinum, has a significant impact on the yield and quality of cucumber. The use of chemical compounds, agronomic managements and resistant varieties is not effective in controlling Fusarium diseases. Biological control is an environmentally friendly method with high control efficiency and low toxicity. It is also important to maintain the ecological balance and sustainable development of agriculture. In this paper, four actinomycetes strains named A01、B01、 B04、CT205 were isolated from the soil of the Zijin Mountain in Nanjing, Jiangsu, China. The Actinomyces strain CT205 showed maximum antagonistic effect in vitro and was screened for further experiments. The antagonistic Actinomyces CT205 was identified and later, a bio-organic fertilizer was developed using Actinomyces CT205 and its biocontrol effect against the cucumber Fusarium wilt was evaluated in pot and field experiments. The results obtained were as follows:Antagonistic Actinomyces CT205 was identified as Streptomyces albospinus by morphological traits, physiobiochemical traits and 16S rRNA sequence analysis. Actinomyces CT205 showed better antagonistic effect against Rhizoctonia cerealis, F. oxysporum f. sp. cucumerinum and Phytophthora parasitica var. nicotianae than other three Actinomyces. The fermentation supernatant liquid of strain CT205 also had antagonism to banana root-knot nematodes. The corrected mortality of banana root-knot nematodes was reached up to 95%. Antagonistic strain CT205 was confronted with F. oxysporum f. sp. cucumerinum in vitro. The edge of pathogen mycelium showed a significant change; the diaphragm of the mycelium became wide and folded. The tips of the mycelia became enlarged and expanded and the protoplast was leaked.The results of two pot experiments showed that the disease control of cucumber wilt disease using Actinomyces CT205 suspension alone was 18.8%and 51.9% respectively. The reason for differences between control effects was that Actinomyces CT205 suspension was mixed with soil in the first pot experiment but irrigated in the second pot experiment. Moreover, disease control of cucumber wilt disease with bio-organic fertilizer was 83.6% and 81.9%, respectively. The application of bio-organic fertilizer also promoted the growth of cucumber. Plant peroxidase (POD) activity value of bio-organic fertilizer treatment was 35.68U g-1 min-1, increased by 130.6% compared with control. Soil urease and invertase activities of bio-organic fertilizer treatment were also increased by 26.8% and 29.2%, respectively, compared with CK. The change in soil microorganisms was determined by plate count and PCR-DGGE analysis. The result showed that the application of bio-organic fertilizer could increase the quantity of Actinomycetes and decreased the quantity of F. oxysporum. The bacteria quantity was decreased, but bacterial diversity was increased, while fungi quantity and diversity was both decreased compared with CK.The results of field experiment showed that control effect of bio-organic fertilizer treatment to cucumber wilt disease was 55.6%. After the application of bio-organic fertilizer, cucumber plant height and stem diameter were increased by 49.3% and 12.8%, respectively, compared with CK. The cucumber yield of bio-organic fertilizer treatment was 5.5×103 kg mu-1, increased by 41.2% compared with CK. Soil urease and invertase activities were also increased in different degree compared with CK. The pathogen counts were changed in the rhizosphere soil of healthy plants, and soil microbial community structure was improved.