The Effects And Mechanisms Of Bacillus Amyloliquefacien Strain SQY162 On Biological Control Of Bacterial Wilt Of Tomato

Tomato is one of the most important economic crops.Due to continuous intensive cultivation and improper managenent mode,the soil-bome diseases of plants increase year by year in China.Tomato bacterial wilt caused by Ralstonia solanacearurm is one of the most serious soil-bome vesicular pathogens.The R.solanacearum from different hosts have significant differences in biovar and pathogenicity,so it is difficult to control tomato bacterial wilt.Recently,biological control of soil-borne disease has been becoming an impressing way to suppress the bacterial wilt with its security and environmental friendly advantages.In this study,one antagonistic strain Bacillus amyloliquefaciens SQY162,isolated from tobacco rhizosphere soil showed strong antagonistic effect against R.solanacearum.The stain SQY162 was used in pot experiments to assess the control effects of tomato bacterial wilt.To determine possible biocontrol mechanisms,inducing tomato systemic resistance and the colonization ability of strain SQY162 in tomato rhizosphere soil were studied.The research results are listed as follows:1L The strain SQY162 showed highly antagonistic effect against R.solanacearum ZJ3721 with a 37mm diameter inhibitory halo on NA medium plate,and could also inhabit some fungal pathogens.The antagonistic bacterial SQY162 could significantly reduce the disease incidence of tomato wilt.Application of SQY162 with different fertilizers could significantly affect biocontrol effects.Biocontrol efficiency in application of SQY162 with composed pig manure reached to 71.67%,which was better than that with pig feces(61.87%).What's more.different inoculation methods of SQY162 could also significantly affect biocontrol effects.With root-dipping inoculation of SQY162 in starch solutions,the biocontrol efficiency reached to 77.73%,which was better than that by drenching treatment with SQY162(64.8%).Furthermore,the population of SQY162 in the rhizosphere soil by root-dipping inoculation with SQY162 in starch solutions was higher than that by drenching treatment with SQY162.However,the variation trend of R.solanacearum compared to the variation trend of SQY162 was opposite in both inoculation methods.The results of pot experiments showed that application of antagonistic strain SQY162 could also promote the growth of tomato plants.The tomato plant fresh weight,dry weight,stem diameter and plant length were all significantly higher in SQY162 treatment than in CK treatment.The application of biological organic fertilizer containing SQY162 strain(BOF2)showed the best promotion effect.The plant shoot fresh weight,shoot dry weight,root fresh weight,root dry weight,height and stem diameter in treatment of BOF2 were more l.93,2.78,2.61.4.62,L.1,and 1.51 times respectively than that in CK.2.To further study the mechanism of bio-control of the tomato bacterial wilt by strain SQY162,the expression levels of the defense-related genes of tomato were determined from 1 to 15 days after inoculation of SQY 162.The expressions of those defense-related genes were not stimulated by SQY 162 at the first day inoculation except that of Pin2(jasmonic acid pathways,JA pathways).The expression of Pin2 increased and was maintained at a relative stable level until 5 days after the SQY 162 inoculation.At 3rd and 5tih day after the SQY162 inoculation,PR-1 a gene(salicylic acid pathways,SA pathways)expression increased 3.89-and 4.06-fold compared to the control treatment.Similar results to PR-1a gene expression were also observed in GluA gene(SA pathways)expression.However,the results showed that the expressions of PR-jb and LoxA genes(JA pathways)of tomato were suppressed by the application of SQY 162 from 1 day to 15 days.After 15 days inoculation,the expression levels of defense-related genes of tomato described above all decreased except that of PR-1a with 1.94-fold increase in contrast to the control.What's more,the enzyme activities of SOD,CAT,and POD of tomato increased by 3.96,2.95 and 27.46%,respectively,with the application of SQY 162 compared to CK.3.Combining application of SQY 162 and R.solanacearum in two different soils(healthy,pathogenic)showed that there was a negative correlation between the population of SQY 162 and R.solanacearum in the soils.Results indicated that the colonization of R.solanacearuwm in pathogenic soil were higher than that in healthy soil.The number of R.solanacearurYm decreased gradually,and finally maintained at about 7.0 log cfu/g dw soil.In contrast,the population of SQY 162 in pathogenic soil would decline faster than that in healthy soil.SQY162 could produce antibiobites surfactin in soils,because the content of antibiobites surfactin was significantly higher in all the treatment inoculated with SQY162 than in control.And more,surfactin production could be stimulated by exudate of tomato and pathogen R.solanacearum.4.The result of the chemotaxis assay showed that the pathogen R.solanacearurrm could be attracted by organic acids since the population of R.solanacearum in the presence of individual organic acid was all significantly higher than that of control.But different organic acid showed different attraction effect.The R.solanacearum was mostly attracted by citric acid.Organic acid also could promote the fiofilm formation and pathogen related gene expression of R.solanacearum.The highest biofilm intensity of R.solanacearum was observed in the presence of citric acid followed by fumaric acid and succinic acid.The transcription levels results suggested that in presence of citric acid could significantly increase the transcripts levels of PhcA,epsE,hrpB,xpsR,egl,pme and tek by 14.52-,10.10-,3.49-,16.10-,6.67-,7.32-,and 22.58-fold.The influences of organic acid and the SQYUV 162 on the disease index of tomato bacterial wilt were determined in the hydroponic system.The results suggested that addition of organic acid could increase the disease index of tomato bacterial wilt.The disease index of the treatments in the presence of citric acid without the inoculation of SQYUV 162 was 94.78%,which was the highest than that of the other treatments in the hydroponic experiments.The results also showed that inoculation of SQYUV 162 in all the treatments in presence of individual organic acid could significantly decrease the disease index of tomato bacterial wilt.Nevertheless,the highest suppression ratio was in the treatment addition of citric acid and SQYUV 162,as high as 72.67%.