Study On Colonization Capability And Growth Promotion Of Antagonistic And Endophytic Streptomyces

We studied the colonization capability of four Streptomycete strains, which wereantagonistic to Verticillium dahliae Kleb., and the effect of these strains on growth, leafphotosynthetic characteristics and rhizosphere actinomycete community of cotton seedlings.The results are as follows.1. The indigenous microorganisms in soil and inoculated V. dahliae Kleb. had significantinfluence on the counts of Streptomyces Z₉and25.①The populations of Streptomyces Z₉and25in sterilized soil were significantly higher than the unsterilized treatment. The increase ofStreptomyces population was inhibited by indigenous microorganisms in soil.②Themultiplication and survival of Streptomyces25in soil were influenced by V. dahliae. Insterilized treatment, the population of Streptomyces25was increased by69.84%whencultured for21days compared to7days, while the population was decreased by4%in theinoculated V. dahliae treatment.③The actinomycete diversity and the populations ofindigenous actinomycetes of unsterilized soil were increased in the inoculating StreptomycesZ₉and25treatments.2. The actinomycete counts in cotton’s rhizosphere were significantly influenced byantagonistic Streptomyces inoculation.①Actinomycete counts from cotton root and rootsurface were improved. In the Z₉and Z₁₃individually inoculation treatments, actinomycetecounts from root surface were increased by45.9%and20.3%,respectively, compared to thecontrol; and actinomycete counts from cotton root were increased by428.9%and339.0%resprctively in the Streptomyces25and Z₁₃individually inoculation treatments（P＜0.05）.②The predominant actinomycete counts in cotton root were increased by Streptomycesinoculation. The populations of predominant actinomycetes in cotton root treated by fourStreptomyces inoculation were1.7to54.1times higher than the control treatment.③Theincrease of actinomycete counts in cotton root was beneficial to the growth of cottonseedlings. In the Z₉and Z₁₃individually inoculation treatments, the increased of actinomycetecounts in cotton root lead to the increase of height, fresh weigh and root fresh weigh of cottonseedlings. 3. The colonization of antagonistic Streptomyces have significant influence on promotiongrowth and leaf photosynthetic characteristics of cotton seedlings.①Z₁₃、25、X4inoculatedboth individually and mixed with V. dahliae were steadily colonized in root of cotton. After60days of inoculation, the population of each strain was102cfu/g in the root of cotton. Z₉was colonized in root of cotton after topdressing with Streptomyces，but it had minimumpopulation.。②The fresh plant weigh and fresh root weight of cotton seedings were promotedby four strains of Streptomyces,Z₉had steady growth promotion effect on cotton.The cottonroot length and fresh root weight were increased by56.6%～58.1%and45.9%～54.0%seperately after Z₉inoculated both individually and mixed with V. dahliae（P＜0.05）③Streptomyces25、Z₉、Z₁₃significantly promoted the net photosynthetic rate, transpirationrate, stomatal conductance and decrease the intercellular CO2concentration of cottonseedlings（P＜0.05）.4. Endophytic actinomycetes were isolated from cotton root.①16S rRNA sequenceanalysis showed that all of the seven endophytic actinomycete isolates, with differentmorphological characteristics, were S. diastaticus subsp. ardesiacus.②The seven strains ofS. diastaticus subsp. ardesiacus had antagonisitic activity to V. dahliae Kleb. and Fusariumsulphureum. The diameters of inhibitory zones were ranged from12to19mm and axenicfermentation extracts of endophytic actinomycetes also had inhibited pathogenic fungi. Theinhibitory rates of axenic fermentation extracts of A6to F. solani, F. sulphureum and V.dahliae Kleb. were93.0%,80.5%and53.8%, respectively.③All axenic fermentation extractsconcentrations of A6significantly promoted radicle length and hypocotyls length of cotton.The increase of radicle length was ranged from24.3%to43.5%and the increase ofhypocotyls length was ranged from and11.7%to28.6%, compared to the control trentment.