The Effects Of Combination Of Biocontrol Bacteria And Biochars On Supperession Of Soil-Borne Tomato Bacterial Wilt

Tomato wilt is a destructive soil-borne disease caused by Ralstonia solanacearum and bacterial wilt of tomato seriously restricts the tomato production,as a result,control of this disease is an urgent need.During the epidemic of R.solanacearum,some of the nutrient substances in the root exudates of the host will induce the proliferation of R.solanacearum in the rhizosphere and increase the incidence of bacterial wilt.The root exudates play an important role in the process of root invasion of R.solanacearum.As an environment friendly method,biological control has become a hot spot of research in recent years.The stable colonization of biocontrol bacteria in the rhizosphere is the key to biocontrol efficacy,However,the effect of biocontrol bacteria is not stable because of the complexity of environmental and biological characteristics in soil.As a porous material with adsorptive properties,biochar has a great potential for suppression of soil-borne diseases.Adsorptio ability of biochars can transfer root exudates from rhizosphere,and its porous structure can provide shelter for most bacteria and fungi.Therefore,we proposed to use biochar as a carrier of biocontrol bacteria to improve the rhizosphere colonization of biocontrol bacteria,and finally improve the control efficacy of bacterial wilt.In this study,we studied the effects of combination of biochar and biocontrol bacteria(Bacillus amyloliquefaciens T-5 and Pseudomonas fluorescens CHAO)on tomato bacterial wilt caused by R.solanacearum.Focusing on the "resources" and "space" transfer,we revealed the mechanism of combination of biochar and biocontrol bacteria on suppression of tomato bacterial wilt.The results are listed as follows:1.Six biochars made by different feedstock were used in this study.The total carbon content of the six biochars were high,but there were significant differences in total carbon content among the six biochars.The highest total carbon content was maize straw biochar(74.69%),and the lowest was apricot shell biochar(24.41%).The total nitrogen content of the six biochar is very low(?0%).The pH value of the all six biochars was more than 8,as a result biochar application may increase soil pH.The EC values of the six bichars were 1-4 ms/cm.Wood biochar and coconut shell biochar showed higher BET surface area than other biochars,while maize straw biochar and rice straw biochar showed high cation exchange capacity(CEC).These two properties had a great influence on the adsorption capacity of biochars.2.Pot experiment showed that the addition of biochar could significantly reduce the population of R.solanacearum in tomato rhizosphere,and the incidence of tomato bacterial wilt could be reduced by more than 30%compared with the control treatment.The addition of biochar could increase the colonized population of T-5 and CHAO and inoculation method had no significant effects on the population of biocontrol agent in rhizosphere.We found that the efficacies of maize straw biochar,rice straw biochar and wood biochar on decreasing the disease incidence,decreasing the population of R.solanacearum and increasing the colonization of biocontrol bacteria were higher than that of other three biochars.In addition,the colonization ability of T-5 in the rhizosphere is stronger than that of CHAO.3.Biochar could effectively adsorb the root exudates and affect the growth of R.solanacearum.Additionally,biochar can significantly reduce the population of R.solanacearum in the suspension of bacteria by adsorption.The adsorption capacity is generally more than 50%of the concentration of bacteria and the adsorption efficacy of wood biochar(-90%)is higher than the other biochars,R.solanacearum showed chemotaxis ability to different carbon source occurs,but the addition of biochar can effectively limit the movement of R.solanacearum to the carbon source.This revealed that biochar has the ability to adsorb and restrict R.solanacearum,which can effectively limit the its movement,avoid its escape from biochar surface.Among the six biochars,wood biochar,rice straw biochar and maize straw biochar showed better adsorption than the other biochars and can be preferred as a potential carrier of biocontrol bacteria.In the growth medium of simulated root exudates,the biocontrol bacteria T-5 and CHAO could inhibit the growth of R.solanacearum by using simulated root exudates and could use the simulated root exudates to produce active substances which had inhibitory effects on R.solanacearum.Also under the same conditions,T-5 has higher antibacterial ability than CHAO.In conclusion,our results revealed that biochar can be used as biocontrol bacteria inoculating carrier,and can adsorb and transfer root exudates to decrease the incidence of tomato bacterial wilt.At the same time,root exudates adsorption of biochar increased the adsortption of R.solanacearum by biochar.Additionally,the biocontrol bacteria can inhibit the growth of R.solanacearum by using root exudates,and under the context of adsorption and restriction of biochar,it is difficult for the R.solanacearum to escape from the biochar surface and invade the host.Our results reveals the mechanism of combination of biochar and biocontrol bacteria for control of soil-borne tomato bacterial wilt and provides theoretical bases for the application of biochar for disease control.