Effect Of Avirulent Strains Of Ralstonia Solanacearum On Tobacco Bacterial Wilt In Greenhouse

Tobacco bacterial wilt,which is a kind of bacteria disease caused by Ralstonia solanacearum and greatly affects the yield and quality of tobacco production,is one of the most destructive diseases on the tobacco crop and is hard to control.Biocontrol is an impromising way to control this tobacco disease. Avirulent strains of Ralstonia solanacearum has been found to be effective to the pathogen under similar ecological conditions,while it exerts a little negative influence on entironment.In the study several avirulent isolates were got from disease samples in eggplant,tomato,tobacco and pimiento planting area in Chongqing,and they were acquired by ultraviolet mutation and culturing the pathogen in succession. These avirulent isolates were screened for antagonistic bacteria aginst the pathogen,and were tested to control the disease in greenhouse.Meanwhile the activities of defensive enzymes and the content of pathogensis-related prcteins(PRP)in the tobacco plants inoculated by these avirulent strains were measured.The main results are listed as follows.1.Among June to September 2006,a number of 184 samples were collected in vegetable or tobacco planting area in Bishan county,Beibei borough,Baishiyi town Jiulongpo brough,Jiangjin brough,Youyang county and Fuling brough,including 67 samples of eggplant,42 ones of tomato,38 ones of tobacco,37 ones of pimiento which were infected by the pathogen.A total number of isolates that were conserved and identified primarily was 138,including 22 virulent isolates accounting for 16%of the total isolates and was composed by 13 ones from diseased eggplant,6 from diseased tobacco,2 from diseased tomato,1 from diseased pimiento,and 116 avirulent isolates accounting for 84%of the total isolates and composed by 41 ones from diseased tomato,41 from diseased eggplant,21 from diseased pimiento,13 from diseased tobacco.2.One hundred and sixteen avirulent isolates which were isolated directly,42 ones which were obtained throng ultraviolet radiation treatment,and 19 ones which were acquired by culturing the pathogen in succession,had been assayed for antagonistic activity in the study.Sixty two of the avirulent isolates constituted by 61 from direct isolation and 1 from ultraviolet mutation,were found antagonistic against Rsolanacearum solanacearum.Afer the second screening,21 had an inhibition zone =1cm in width,13 had an inhibition zone between 0.5cm and 1cm in width,28 had an inhibition zone =0.5cm in width.Employed the 21 isolates,spaying and fixing bacterium for screening were compared.The results showed that most of the isolates inhibition zones gained by spaying were wider than those from fixing bacterium,except numbered Tmt3-2-1 and TbYYk1-1.The conclusion was that the method of spaying was handier and quicher than the other,and was more applicable for antagonizing test.3.The greenhouse experiment on tobacco plants was carried out with the 21 isolates,the results indicated that most of them could postpone the disease occurrence 7 days,obvious abnormity did not appear on young tobacco plants that showed the 21 isolates may be harmless to tobacco plants.Of 5 isolates,the relative control efficacy was =60%,the others' was＞60%.Six isolates were chose for the second greenhouse experiment,according the results of the first test and development on media,the results showed that comparing to trentment with CKRs,each treatment with L6-3,Tmjd1-3,Au004-1,TbYYk1-1 and Aujd8-2-1 could postpone the disease occurrence 14d,6d,5d,2d and 1d,respectively.L6-3,Au004-1 and Tmjd1-3 presented better controlling effect on tobacco bacterial wilt,the relative control efficacy was 80.83%,77.5%and 75%respectively at 30 days after treatment,and the relative control efficacy of L6-3 was the highest.4.The activities of phenylalanineammonium-lyase(PAL),peroxidase(POD),polyphe-noloxidase (PPO)and the content of pathogensis-related proteins(PRP)in tobacco were determined,after treated by Au004-1 and Tmjd1-3 growing better on NA media and owning the better control effect.It was found the the activities of PAL,POD,PPO and the content of PRP in tobacco increased.Then the results suggested that the impacting mechanism of avirulent strains of Ralstonia solanacearum on tobacco bacterial wilt was directly antagonistic action besides,might be induced resistance.