Cucumber Growth Promotion And Wilt Disease Suppression Of Bacillus Subtilis SQR9 And Their Mechanisms

Cucumber is a most important vegetatable in the world. However, cucumber production has been restricted due to long-term monoculture system. Fusarium wilt of cucumber is one of the most destructive worldwide diseases of cucumber. Breeding of culitvars with resistance to Fusarium wilt, chemical application and field management are among the solutions to control this disease. It is necessary and urgent to find a better way to ensure cucumber industry both in China and in the world. Biocontrol has been proving economical and environmentally friendly to such soil-borne disease.Application of bioorganic fertilizers containing the antagonists either in nursery or in transplanted soils was carried out to investigate effects of three types of bio-organic fertilizers (BIOⅠ, BIOⅡandⅢ) made from these two antagonists on the control efficiency of Fusarium wilt of cucumber and plant growth. We also studied the colonization of the two strains on cucumber roots. Results of pot experiment showed that the incidence of Fusarium wilt in control was 100%, while the incidence rate of treatment BIOⅢwas only 13.73%. Meanwhile, the biomasses of cucumber treated with BIOⅠ, BIOⅡand BIOⅢ, were 2.55,2.46 and 2.58 times of the control, respectively. Application of BIOⅡand BIOⅢcould effectively reduce the quantity of Fusarium oxysporum in cucumber rhizosphere to 103 copies/g soil detected by real-time PCR, but 107 copies/g soil of Fusarium oxysporum was found in the control. SQR9 and T37 could effectively colonize on the cucumber root surface and thus occupied the ecological sites on the rhizoplane. These results illustrated that application of BIO could not only effectively suppress the Fusarium wilt of cucumber, but also promote the growth of cucumber plants.Results of the promoting experiment of showed:Bacillus subtilis SQR9 could effectively promote the growth of cucumber. The shoot height of cucumber treat with 1,2, 3 were 1.46,2.21 and 2.30 times of the control, according to control, the total root length of the cucumber increased 26%,54%,77%.Lipopeptides produced by Bacillus subtilis SQR9 were extracted with methanol from the precipitate which was obtained by adding 6 mol/L HCl to the cell-free culture broth.The in vitro inhibition rates of strain SQR9 to F. oxysporum in Petri dishes reached to 68.2%. Five lipopeptide substances were isolated from the fermentation liquid of strain SQR9 by high performance liquid chromatography (HPLC), and all of them were confirmed as antagonistic substences against phytopathogens.The molecular weight of the part of the strain SQR9 antimicrobial substances were measured in the LC-MS, and we speculated that the antagonistic substance of the strain SQR9 containing two kinds of Lipopeptides,Fengycin and Bacillomycin D.Genes of two antibiotic families such as bacillomycin and fengycin from SQR9 were detected by PCR reaction. Indole-3-acetic acid and GA3 were isolated from the fermentation liquid of strain SQR9 by high performance liquid chromatography (HPLC). The result showed that the concentration of IAA in the medium is 52.03mg/L. The promoting experiment revealed that the volatile components produced by Bacillus subtilis SQR9 trigger plant growth promotion in Arabidopsis.We conclude that the BIO could effectively control the cucumber Fusarium wilt by improving the cucumber rhizosphere microbial diversity, reducing the incidence rate and promoting plant growth. SQR9 and T37 could effectively colonize on the cucumber root surface.