Effect Of Succinic Acid On Soil-borne Bacterial Wilt Via Regulating Soil Microbioal Community

Root exudates are important substances secreted by plant roots.These substances are not only used as nutrients by rhizosphere microbes for their growth and reproduction,but also play important roles in regulating the structures,functions and interactions of rhizosphere microbial communities.Studies have shown that the components of root exudates can affect the occurrence of soil-borne diseases by regulating the community structure of rhizosphere microbial community.For example,phenolic acids and organic acids can reduce disease incidence of tomato bacterial wilt.However,it is still unclear which substances in root exudates play a key role in affecting soil-borne disease,in further regulating what kind of certain species.Therefore,this study investigated mechanisms of root exudates on occurrence of soil-borne diseases.In order to answer the above questions,this study used Ralstonia solanacearum as the model pathogen,which causes soil-borne bacterial wilt.This disease brings great harm to agricultural development of China due to its wide-spread and severe outbreak.It has caused.Based on previous study,six kinds of root exudates with effects of disease suppression,which are salicylic acid,coumaric acid,succinic acid,L-rhamnose,Lalanine,D-Mannose,wereselected.six root exudates(with final concentration of 0.1m M)were added to tomato plants via root drench,to investigate their effects on disease incidence of tomato bacterial wilt.Succinic acid was screened out as the best treatment of disease suprresion.After that,effects of succinic acid on the occurrence of tomato bacterial wilt under two soil systems(red soil and yellow-brown soil)were tested.According to the results of high-throughput sequencing,effects of succinic acid on the diversity,structure and co-occurrence network of bulk soil and rhizosphere soil microbial communities were analyzed,based on which the key microbes affected by succinic acid were determined.Finally,the key microbes were isolated and effects of succinic acid on the ability of Ralstonia inhibition,antagonism,and siderophore production were investigated.The main findings are as follows:1.In the greenhouse experiment,six root exudates with final concentration of 0.1m M were added by root drench.The results showed that compared with the control,Lalanine,coumaric acid,succinic acid,L-rhamnose,salicylic acid could significantly reduce disease incidence of tomato plants.Among them,succinic acid had the best effect on disease suppression.In addition,succinic acid was added to two soil systems(red soil and yellow-brown soil)to investigate effects on tomato bacterial wilt under different soil systems.The results showed that compared with the control,succinic acid had no significant effect on the dry weight of aboveground and belowground and height of tomato plants in the two soils.Succinic acid significantly reduced disease incidence of tomato plants in both soils.2.We further investigated effects of succinic acid on the microbial communities in bulk soil and rhizosphere soil under two different soil systems(red soil and yellowbrown soil).The results showed that the addition of succinic acid significantly increased OTU richness of red soil,but had no significant effect on yellow-brown soil.succinic acid had no significant effect on the Bate-diversity and bacterial community structure of the two soil systems were not affected.Relative abundance of Gemmatimonadetes in red soil increased after treated with succinic acid.Lefse analysis showed that succinic acid significantly increased relative abundance of Nitrosospira,Streptomyces,Gemmatimonas and other bacterial species.Meanwhile,succinic acid increased negative interactions of bacterial communities in red soil and yellow-brown soil,indicating that succinic acid may inhibit the occurrence of tomato bacterial wilt by enhancing antagonisms among soil microbes.3.According to high-throughput sequencing,key soil microbes were isolated with TSA,Gause No.1 and V8 medium,and 78 strains Bacillus spp.and 30 strains Streptomyces spp.were obtained in total.Subsequently,impacts of succinic acid on the Ralstonia inhibition,antagonisms and siderophore production of the key microbes were investigated in the microplates.The results showed that succinic acid could significantly enhance the inhibitory ability of 8 Bacillus spp.against R.solanacearum,of which 5 strains significantly inhibited the growth of R.solanacearum through antagonistic competition.Siderophore production of 2 strains Bacillus spp.increased after adding succinic acid.In addition,succinic acid significantly improved the antagonistic competition between 7 strains of Streptomyces spp.and R.solanacearum,and siderophore production of 4 Streptomyces spp.