Isolation And Biological Feature Study Of Anactinomyces Strain And Its Biocontrol Effect Against Tobacco Bactetrial Wilt

Tobacco bacterial wilt,one of the main soil-borned diseases of tobacco caused by Ralstonia solanacearum,threatens production of tobaccot in the world.In China,it widely occurs in the producing areas of tobacco,especially in Yangtze and southern areas.To explore the biological control measures for controlling tobacco bacterial wilt is very important to tobacco production.This dissertation focused particularly on the isolation and identification of an antagonistic strain and optimization of fermentation condition and its biocontrol effect of tobacco bacterial wilt.The main results are as following:(1)From the soil samples of tobacco in FuQuan city of GuiZhou.6 actinomycetes strains were isolated from the soil samples using dilution method,among which 6 strains were screened to show antagonistic activity against Ralstonia solanacearum.Strain A27 showed the best inhibition to Ralstonia solanacearum,the diameter of antibacterial circle of A27 reached to 42.6 cm.(2)The substrate mycelia of strain A27 have no partition,the aerial mycelia are pink,the spores are oval.According to is morphological,cultural physiological,biochemical characteristics and 16S rRNA gene sequences analysis strain A27 is identified as Streptomyces termitum.(3)The fermentation conditions of strain A27 were studied.The experiment results indicated that the optimum fermentation condition for strain A27 to produce the best activity were as following:2.0%soluble starch as carbon source,0.3%soy peptone as nitrogen source,0.075%NaCl,0.025%MgSO4,the initial pH of 6.0-8.0,inoculation level of 6%,80 mL medium in 250 mL flask,incubation at 28 ℃ and 170 r/min for 120 h.(4)Results in pot trail showed that the inoculation of strain A27 can effectively prevent and control the occurrence of tobacco bacterial wilt.Five treatments were designed as following,application of biological organic fertilizercontainning strain A27(BOF),application of A27 cell suspension by irrigation root(G27),application of A27 cell suspension and liquid amino acid together by irrigation root(G27+AA),application of A27 cell suspension by dipping root(Z27)and application of A27 cell suspension with 15%starch by dipping root(Z27+D).The control efficiency of those treatments above against bacterial wilt are over 52.8%,the control efficiency of treatments Z27 and Z27+D were respectively 60.4%and 64.2%,higher than other treatments.In addition,after 60 days experiment,the number of strain A27 at rhizosphere of all treatments were more than 105 CFU/g soil,which showed that the strain A27 had good colonization in the rhizosphere of tobacco,the number of strain A27 of Z27+D treatment was the highest 1.66 ×106CFU/g soil,which showed that application of A27 cell suspension with 15%starch by dipping root can improve the colonization of strain A27 in the rhizosphere of crops.(5)Application of strain A27 and bioorganic fertilizer could increase POD,CAT and SOD activity and reduce MDA contents in tobacco plants.