Effect Of Fusarium Oxysporum On Bacterial Diversity In Rhizospheric Soil Of Watermelon Plant

Soil microorganisms are closely related to the stability of soil ecosystem and soil system health.Soil microorganisms play an important role in protecting the healthy growth of plants and controling plant disease.Fusarium oxysporum is the soil borne pathogens that cause fusarium wilt of watermelon.The study on the relationship between soil microorganism and soil-borne diseases induced by Fusarium oxysporum possesses important theoretical significance,to reveal the microbial mechanism of soil-borne diseases and to control fusarium wilt of watermelon using beneficial microorganisms.In this paper,fusarium wilt of watermelon was induced by artificially inoculating different concentrations of spore suspension of Fusarium oxysporum;the effects of Fusarium oxysporum on rhizobacterial diversity were studied with a combination of the traditional culture method and high-throughput sequencing;the changes of bacterial diversity,function diversity,soil enzyme activity and beneficial rhizobacteria caused by different amounts of Fusarium oxysporum were comparatively studied.This has important theoretical and realistic significance for clarifying microbiological principle on the occurrence and spread of the fusarium wilt of watermelon.The major findings are as follows:1.Watermelonseedlings were inoculated with 10~3、10~4、10~5、10~6、10~7 cfu/m L spore suspension of Fusarium oxysporum(the treatment groups were recorded as 3F,4F,5F,6F and 7F,controlgroup was recorded as PC).It was found that as the spore suspension of Fusarium oxysporum increased,the disease index of watermelon increased,and the highest index was0.83.2.Different kinds of rhizosphere soil microbes were counted using different selective medium.As the disease index increased,the number of bacteria and actinomycetes decreased,and the number of fungi increased;the number of phosphate-solubilizing bacteria and cellulose-degrading bacteria decreased.The rhizosphere soil suspension was added to the Biolog ECO plate for culture,it was found that during the log phase of culture,activity of microbial communities(AWCD)increased first and then decreased with the index rising;compared with PC,the Shannon index,Simpson index and Mc Intosh index of each group were not significantly different;richness index showed significant differences highest increased by 8.32%;on different types of carbon source utilization communities,the dominance of carbohydrate metabolism group and Carboxylicacidsmetabolism group in the rhizosphere microorganisms of diseased plantshas increased.3.The ability of phosphate-solubilizing,production of ACC deaminase,siderophore production and antagonistic ability against plant pathogenic fungi for dominant bacteria in each group were determined.With the increase of disease index,the number of antagonistic rhizobacteria against pathogens increased;Based on the 16S r DNA sequencing,Novosphingobium sp.in Alphaproteobacteria and Arthrobacter sp.in Actinobacteria in the PC are the dominant bacteria;Pseudomonas sp.in Gammaproteobacteria was the dominant bacteria for the treatment(7F)with high disease index.Plant growth-promoting characteristics and species diversity were further studied for rhizobacteriain PC and 7F group with highest disease index.It was found that the relative abundance of phosphate-solubilizing bacteria in the treatment with the inoculation of Fusarium oxysporum watermelon decreased by 30%,and the relative abundance of siderophore-production bacteriaand antagonistic bacteria increased by 20%and 8%,respectively;the rhizobacteria of PC and 7F were distributed in 17 genera of 6 families and 17 genera of 5 families,respectively.In the family level classification,Actinomycete(38%),Alphaproteobacteria(20%)and Firmicutes(18%)were the main dominant communities for rhizobacteria of PC,followed by Betaproteobacteria(12%),Gammaproteobacteria(10%)and Bacteroidetes(2%);in the treatment with highest disease index(7F),Actinobacteria(40%),Gammaproteobacteria(28%)and Alphaproteobacteria(16%)were the main dominant communities,followed by Firmicutes(12%),Bacteroidetes(4%);and Betaproteobacteria was not found.In the genus level classification,Arthrobacter sp.,Bacillus sp.and Pseudarthrobacter sp.were the main dominant bacterial communities for rhizobacteria of PC,and Pseudomonas sp.,Arthrobacter sp.and Pseudarthrobacter sp.were the main dominant bacterial communities for rhizobacteria of the treatment with highest disease index(7F).There were some characteristic bacterial communities,but not dominant bacterialcommunities in PC group and 7F group,respectively.4.The diversity of unculturablerhizobacteria was studied by using Illumina Mi Seq High-throughputsequencing technology.In the level of family,compared with the control(PC),with the increase of disease index,the relative abundance of Actinobacteria and Firmicutes decreased in the treatments with the inoculation of Fusarium oxysporum,respectively,the highest decline of 5.77%and 0.6%;the relative abundance of Proteobacteria and Bacteroidetes increased by up to 5.82%and 5.33%,respectively.At the level of genus,with the increase of disease index,the relative abundance of Bacillus sp.decreased.In summary,inoculation of Fusarium oxysporum changed dominant rhizobacteria,speciesdiversity,bacterial communities with multiple physiologicalfunctional and plant growth-promoting characteristics.The isolated strains with plant growth-promoting characteristics and antagonistic characteristics will provide valuable resources for the control of fusarium wilt of watermelon plant and research and development of novel biological biologicagent.