The Effect Of Antibiotics On Population Of Endophytic Bacteria And Biocontrol Of Bacterial Wilt In Eucalypt And Tomato

Eucalypt bacterial wilt?a systemic vascular tissue disease caused by Ralstoniasolanacearum, was a devastating soil-borne disease and caused enormous losses toEucalyptus industry. In this study, the relationship of E. urophylla and tomato diseaseresistance and population of endophytic bacteria was explored by the study of effect ofantibiotics on population of endophytic bacteria, and the effect of endophytic bacteriapopulation change on control of bacterial wilt with antagonistic bacteria was studied byinoculating antagonistic bacteria to E. urophylla treated by antibiotics.1. Screening and colonization of antagonistic bacteria to E. urophyllaUsing plate inhibition zone method and root dipping in the hydroponic system, theantagonistic bacteria to R. solanacearum was screened from Bacillus subtilis Y4andendophytic bacterial strains-CN181, G1, G2, G3, G4, G5, G6, G7and G8-from in vitrogrown seedlings of wheat. The results showed that the strains G1, G4, G6, G8, CN181andY4can form a wide and transparent inhibition zone on KB medium, in6which strain G6,CN181and Y4expressed better antibacterial effect with more than30mm inhibition zone.The further test of effect of above strains to eucalypt bacterial wilt in root dipping in thehydroponic system also showed the control efficiency to eucalypt bacterial wilt, and strainY4not only could postpone disease developing time, but also showed lower rate of diseaseincidence at26.7%than other strains. Based on the above two methods, strain Y4was thebest strain to inhibit R. solanacearum?The colonization of Y4in E. urophylla was studied using the method of root dippingin hydroponic system. The results showed that strain Y4can be detected at3.17×105CFU·g-11d after bacterial suspension treatment, and decreased gradually to7.84×104CFU·g-1at20d after treatment. The above results indicated that in the earlier stage Y4canrapidly colonize E. urophylla in a high density and colonize effectively in a certain periodof time, but the colonization level decreased with time.2. The effect of antibiotics on the colonization in E. urophylla and biocontrol of Y4The effect of antibiotics on the colonization in E. urophylla and biocontrol of Y4wasstudied after E. urophylla was treated by antibiotics. The results show that the proper concentration of rifampicin, tetracycline, streptomycin and chloramphenicol for treatedseedlings of E. urophylla were70,60,50and30mg·L-1. Antibiotic treatment can improvethe control effect of Y4to bacterial wilt in E. urophylla. There was different effect indifferent antibiotis, in which rifampicin and tetracycline showed the best.E. urophylla was treated by different antibiotic and inoculated with strain Y4. Thenumber of Y4colony isolated from E. urophylla was the most at6d after inoculation, andthe treatment with rifampicin was the most. Compared with the hydroponic system, thestability of Y4colonization was better in the soil system But with the extension oftreatment time, the colonization of gradually reduced in both system. The colonization ofY4in different parts of E. urophylla present a decreasing trend in the tissues of roots, stemsand leaves. With the variation in processing time, the different antibiotics treatment havedifferent effects on the colonization of Y4in different parts of E. urophylla. Rifampicinand chloramphenicol treatment are conducive to the colonization of Y4in roots, stems,leaves. At9d streptomycin and tetracycline stimulated the colonization of Y4in the stemsand leaves of E. urophylla, but it was not obvious in the root. At the other processing time,both streptomycin and tetracycline showed inhibition effect to the colonization of Y4.3. The relationship between the endophytic bacteria population structure change caused byantibiotics and the disease resistance of tomato and eucalyptThe effects of different concentrations of rifampicin?20,40and60mg·L-1?on thespecies, amount of endophytic bacteria and disease resistance of tomato was studied. At thesame time, the effect of different antibiotic on the endophytic bacteria population ofeucalypt was also studied. The results showed that tomato plants at4?5leaf stage grewwell after three concentrations of rifampicin treatment. When the concentration ofrifampicin is over60mg·L-1, the plant growth is affected.The different concentrations of rifampicin enhanced or inhibited the endophyticbacteria in the tomato, caused the changes in species and amount of endophytic bacteria indifferent part. And these changes made the tomato plants to improve their resistance tobacterial wilt, especially rifampicin40mg·L-1treated group at the15thday, the incidence oftomato only45.8%.Based on the normal growth of eucalypt, the final concentrations of rifampicin andtetracycline were70and80mg·L-1, and streptomycin and chloramphenicol was both50mg·L-1. The species and amount of endogenous bacteria in eucalypt changed at differenttime when treated with different antibiotic. The incidence was lower in the early stage ofantibiotic treatment than in later stage. This was in accordance with the more abundantendogenous bacteria in the root, stem and leaves of eucalypt. Especially thechloramphenicol treatment, with the most abundant endophytic bacteria, had the lowestincidence of disease, only46.7%. These results indicated that the change of endogenousbacteria population caused by antibiotic can affect the disease resistance of eucalypt.