The Control Effect And Mechanism Of Streptomyces NJU-54 On Tomato Fusarium Wilt

The frequent use of fungicides and unreasonable planting methods have caused tomato crops to suffer from the Fusarium oxysporum,causing tomato Fusarium wilt.Microbial antagonism is an effective method to control plant fungal diseases.Numerous experiments have shown that Streptomyces is an important producer of antibiotics and volatile organic compounds in soil and plants.Streptomyces can prevent plant diseases and promote plant growth in many crops.To learn more about the control effect and mechanism of Streptomyces on tomato diseases,we did this research.We took tomato as the main object and then screened the Streptomyces strain NJU-54 as an antagonist.This research explored the effect and mechanism of tomato plant defense against Fusarium wilt under the intervention of Streptomyces from soil enzymes,soil microbial ecology and plant physiology and biochemistry perspectives.In this study,a strain of Streptomyces named NJU-54 was isolated from soil by screening and identifying.This research evaluated the ability of NJU-54 to inhibit a variety of plant pathogens and Fusarium oxysporum through the plate confrontation assays and cocultivating with fermentation broth.The tomato seedlings pre-inoculated with NJU-54 before cultivated in MS medium.The amount of colonization of NJU-54 in tomato plant was determined regularly.The tomato seedlings were planted in the soil that was pre-inoculated with three concentrations of NJU-54(3.9×105 cfu·g^-1),3.9×106 cfu·g^-1),3.9×107 cfu·g^-1)).The tomato seedlings were evaluated Fusarium wilt disease grade index and control effect after infecting with Fusarium oxysporum consequently.Meanwhile,this study detected the enzyme activity,microbial quantity,microbial community,dominant microbial population of the rhizosphere soil and the activities of POD,PAL,PPO,SOD of tomatoes leaves and roots.For the first time,the experiment used Zymography to analyze the temporal and spatial distribution and activity changes of acid phosphatase,β-glucosidase and chitinase in the rhizosphere soil.This study evaluated the effects of Streptomyces strain NJU-54 on the growth of tomato seedlings under the conditions of soil pre-inoculation with three concentrations of NJU-54.The results of the study are as follows:1)NJU-54 inhibited the growth of various disease fungi.NJU-54 and its fermentation broth had inhibitory effects on Fusarium oxysporum,and the latter had a significant inhibitory effect（p<0.05）.It is found that the strain NJU-54 has the ability to degrade chitin,and the diameter of the transparent circle of chitin degradation is 10.15±0.91 mm.2)After pre-inoculation for tomato seeds with three concentrations of NJU-54（low,medium and high）,NJU-54 colonized inside the tomato seedling plants.There was no significant difference among three concentrations in colonization amount（p>0.05）.The colonization in the fresh tissues of the tomato seedlings was（3.70±0.78）×105 cfu·g^-1)·FW under three concentrations of NJU-54 treatments.3)Soil pre-inoculation with NJU-54 significantly reduced the tomato plant disease grade index（p<0.05）.The control efficiency of tomato Fusarium wilt is 56.21%-65.36% under three concentrations of NJU-54 treatments.The medium concentration NJU-54 treatment(3.9×106 cfu·g^-1))showed the best control effect.The activities of PAL and PPO in tomato seedling leaves increased significantly under three concentrations of NJU-54（p<0.05）.However the activities of PAL,PPO and SOD in the roots reduced under three concentrations of NJU-54.The activity of POD was not changed significantly（p>0.05）.4)After the soil pre-inoculated with NJU-54,the growth range of tomato seedling roots gradually increasesed by the time and the difference between the control and treatments.The difference in root growth range did not affect the distribution mode of rhizosphere enzyme activities mainly along the root system.At the time level,during 7-30 days of tomato seedlings infected with Fusarium oxysporum,the proportions of acid phosphatase and chitinase activity hotspots increased by 12.50% and 10.70%,respectively,in the treatment with low concentration of NJU-54（p<0.05）.The proportion of β-glucosidase activity hotspots decreased significantly in the treatment with low concentration of NJU-54（p<0.05）.At NJU-54 concentration level,when the tomato seedlings were been infected with Fusarium oxysporum 7days,NJU-54 had almost no influences on the proportion of the tomato rhizosphere acid phosphatase,β-glucosidase and chitinase activity hotspots.When the tomato seedlings were infected with Fusarium oxysporum 30 days,the proportions of acid phosphatase and chitinase activities hotspots in the low-concentration group reached the highest value,which were 21.90% and 14.80%,respectively,significantly higher than the control group 13.80% and 6.20%,respectively（p<0.05）.After treatment with medium concentration of NJU-54,the proportion of hotspots of chitinase activity in rhizosphere soil increased significantly（p<0.05）,and the overall acid phosphatase activity of rhizosphere soil increased significantly（p<0.05）compared to the control group.5)Except for the low-concentration NJU-54 treatment,the number of bacterial and fungal OTU in the rhizosphere soil after pre-inoculation with medium and high-concentration NJU-54 were higher than the control group.The addition of Streptomyces strain NJU-54 reduced the dominance of Alcanivorax in the soil.In the group treated with medium concentration,Streptomyces accounted for the largest abundance of bacteria.The relative abundance of Streptomyces,Clostridium and Bacillus in the dominant flora positively correlated with the three concentrations treatments of NJU-54.The relative abundance of Fusarium oxysporum negatively correlated with three concentrations treatments of NJU-54.6)Soil pre-inoculation with NJU-54 significantly promoted the growth of the tomato seedlings,and significantly increased the root dry weight and the content of tomato chlorophyll a and chlorophyll b（p<0.05）.NJU-54 could not produce siderophore or promote phosphate solubilization.NJU-54 promoted the tomato seedling growth by producing auxin.To sum up,Streptomyces became the dominant microbial community in the rhizosphere soil after pre-inoculation of the medium concentration of Streptomyces stain NJU-54 in the soil.The addition of strain NJU-54 effectively inhibited the growth of Fusarium oxysporum in the soil;strain NJU-54 might cooperate with beneficial bacterial to increase the activities of rhizosphere ecological enzymes,thereby accelerating nutrient cycling.At the same time,Streptomyces stain NJU-54 colonized into plant tissues,improving the antioxidant enzyme activity of tomato aboveground tissues,produced auxins to promote tomato growth while prevented plant diseases.