Screening Of Antagonistic Streptomyces Strains And Those Inhibition Activities Against Agrobacterium Tumefaciens

In this experiment, the pathogen of poplar crown gall were isolated and identified. Besides that,bacteria, epiphyte, Streptomyces were used to screen biological control agents against Agrobacteriumtumefaciens, and the physicochemical character of the antibiotic substance was analysed, which will laythe groundwork for biocontrol of the disease by other antagonistic strains in the future. Finally theinhibited role of some bacteriocides and antibiotics on Agrobacterium tumefaciens screened from poplarand its inhibitory isolates was tested to guiding chemical control of poplar crown gall and therequirement of developing rooted-biology pesticide.In the test, eleven isolates with the configuration character of Agrobacterium tumefaciens wereobtained from the poplar root, and all accorded with the characteristic of Agrobacterium tumefaciens bybeing observed on microscope. By infecting on carrot and poplar, only three isolates caused them tocome forth gall. So the three isolates were identified to be pathogen causing poplar crown gall.Twenty three strains of bacteria, eleven strains of fungi, sixty three strains of Streptomyces isolatedfrom two type poplar rhizosphere in this study were tested for antibiotic isolates against pathogeneticisolate A-2 from poplar crown gall. Eight isolates, 26.7% in all the numbers of tested bacteria, showedan antibiosis activity. Thereinto two isolates showed a higher antibiosis activity with a diameter of theinhibition zone ranging from 1.5-3.0 cm, six of them showed a low activity with a diameter of theinhibition zone lower than 1.5 cm. While all the eleven strains of fungi showed no antibiosis activity.On double-layer agar, sixty three strains of Streptomyces isolated from two type poplarrhizosphere were tested for antibiotic isolates against pathogenic strain A-2, and seventeen isolatesshowed an antibiosis activity, the rate of inhibitory isolates was 26.9. Five Streptomyces strains, 29.5%in all the inhibitory isolates, showed a strong antibiosis activity against pathogenic strain A-2 with theinhibition zone above 3.0 cm. The stain named T-S-22 showed the strongest antibiosis activity amongthem with 3.80 cm of zone inhibition, especially. Besides that, five strains of Streptomyces kept in ourlab were tested for antibiotic isolates against pathogenic strain A-2, and three isolates showed a higherantibiosis activity with a diameter of the inhibition zone ranging from 1.5-3.0 cm.The optimum fermentation conditions were determined that 25 ml liquid soybean cake medium(medium B) were added in 250 ml flask and were cultured at 28℃, pH7.0, 180 r/min for 72 h.The antibiotic substance produced by T-S-22 showed a stable antibiotic activity to heat and pH.This substance not only existed in the fermentation liquid but also in the mycelium, it was soluble both in organic phase and in aqueous phase. The antibiotic substance was isolated and purified primary usingthe methods of solvent extraction and Thin Layer Chromatography (TLC). The results showed that theantibiotic substance contained four components. The primary experiments of the substance suggestedthat the bioactivity substance was a mufti-component complex.This study reported the inhibited role of three bacteriocides and four antibiotics on pathogenicstrain A-2 and its inhibitory isolates. The results showed an inhibited role of thiram on pathogenic strainA-2 and its inhibitory isolates. Carbendazim showed a slight inhibition on pathogenic strain A-2 only at4×10³Î¼g/ml. CuSO₄ revealed the strongest inhibition among them not only on pathogenic strain A-2 butalso on its inhibitory isolates. With keeping on culture, the diameter of the inhibition zone becamesmaller and smaller, even disappeared, which meant the period of validity of CuSO₄ was short. Theinhibition zone of four antibiotics had a direct proportion with their consistence, and Streptomycinshowed the strongest inhibited activity on pathogenic strain A-2, oxytetracycline took second place, thanwas tetracycline, agro-Streptomyces was the slightest, showed no inhibited activity at 0μg/ml-5×10³Î¼g/ml.