Azotobacter Bacterials From Banana Rhizosphere Soil Which Can Against Fusarium Oxysporum F.sp.cubense:It’s Isolation Identification And Growth-promoting Effect To Banana Seedlings

Using the preliminarily selective isolation,we obtained 266 strains of nitrogen fixing bacteria from banana rhizosphere soil.Among them,95 strains were actinomycetes.Further study showed that three strains have the capacity of sifting of banana fusarium wilt,with one actinomycetes strain.Comprehensive strain morphological characteristics,physiological and biochemical characteristics and sequencing analyses indicated that the strain 6N-20 was classified as Bacillus amyloliquefaciens,strain 3N-25 was classified as Pseudomonas aeruginosa and strain 8N-10 was classified as Streptomyces noursei.We measured the nitrogen fixation activity of three bacteria in 100 ml Ashby nitrogen free liquid medium culture in vaccination for 15 days.The results showed that the nitrogen content in the liquid medium with strain 6N-20,3N-25 and 8N-10 was 64.67±11.13 mg/kg,37.93±10.93 mg/kg and 2.27±0.88 mg/kg,respectively.By acetylene reduction method,strain 6N-20 was identified as to have strongest nitrogenase activity,which was up to 140.89±3.09 nmol/mL.h.Strain 3N-25 showed high nitrogenase activity,which also reached 78.93±2.96 nmol/mL.h.however,strains 8N-10 had weak nitrogenase activity,which was only 0.549±0.11 nmol/mL.h.We then used the tablet confrontation experiment and spore germination experiment to determine the three bacteria of banana fusarium activity of 4 small kind of antagonism.The experimental results show that strain 6N-20 bacteriostatic belt width is 10.5± 1.22 mm,with spore germination inhibition rate of 70.01%.Strain 3N-25 bacteriostatic band width was 11.4±0.97 mm,with of spore germination inhibition rate of 30.13%.Strain 8N-10 bacteriostatic belt width was 15.5±0.65mm,with the spore germination inhibition rate of 75.09%.Using the method of plate confrontation of broad-spectrum antibacterial activity,three bacteria showed broad spectrum antimicrobial activity of 8 kinds of common diseases of banana pathogens.Prevention effect was carried out for strain 6N-20 with the fermented pot experiment.The results showed that strain 6N-20 fermented liquid harbored the relative control effect at around 67.5%.Fluorescence quantitative polymerase chain reaction(PCR)tracking was used to inspect the dynamic change of pathogenic bacteria content in the potted experiment.The data showed that the number of pathogen with the treatment of only handling a pathogenic bacteria was increasing rapidly,and on the 21st day it reached the peak of 10528827 per gram soil.Number of pathogenic bacteria in 23～27 days decreased sharply and on the 27th day pathogenic bacteria content was about 2605032 per gram soil.Then the number of pathogen showed a slow increase and on the 31st day it reached a new maximum content of soil(about 5758060/g soil).Bacteria abundance was then decreasing steadily,finally achieving a relatively stable value of 1159196 per gram soil.This may be due to the intraspecific competition of pathogenic bacteria over a period of time.For the treatment of dying pathogen bacteria fermented liquid,pathogen quantity decreased rapidly during the first 21 days,from the content about 688019.1 to 773.4315 per gram.It means that fermented liquid of strain 6N-20 in the growth of pathogenic bacteria had good inhibitory effect.When pathogen and inhibitory bacteria achieved a dynamic balance,pathogenic bacteria content has been around 103.we applied the fluorescence quantitative PCR number to accurately measure the numer of banana fusarium in order to provide the mechanism of inhibitory action of antagonism on theoretical basis.Within the treatment of 6N-20 fermented liquid,the banana seedlings chlorophyll content is higher,the relative electric conductivity is lower,the soluble protein content and malondialdehyde content is lower,in comparison with control.Meanwhile,the catalase activity increased while GSH content decreased in this treatment.Altogether,results showed strain 6N-20 fermented liquid have beneficial effects on banana seedlings in response to environmental stress.Strain 6N-20 fermented liquid can obviously promote the plant height,stem diameter,fresh weight,dry weight,root activity,as well as root length.