Soil Microbiome Of Potato Common Scab In Different Areas Of Shandong And Screening Of Biocontrol Strains

The plant rhizosphere microbiome is considered to be the second genome of plant,affecting plant growth,development,nutrition and immunity.Potato is the fourth largest staple crop in the world.Potato common scab(PCS)is one of the main potato diseases caused by pathogenic Streptomyces,which has a huge impact on potato planting and yield worldwide.Previous study has found significant differences in the bacterial community structure,bacterial abundance,and toxin synthesis gene abundance of potato geocaulosphere soil(GS)between samples of the group with high scab severity levels(H)and the group with low scab severity levels(L).However,the current research on the interaction between soil microbiome and PCS is lacking in-depth research.It is not clear that how the factors such as the abundance of pathogenic Streptomyces and bacteria,the physicochemical properties of the root-zone soil(ZS)and the composition and function of bacterial community affect the occurrence of scab.In this study,58 GS and 58 ZS with natural PCS in Xiaofole Village(JF)and Dingguan Village(JD)of Jiaozhou,Lizihang Village(TZ)and Xiaolonghe Village(TX)of Tengzhou were collected in November 2018 in Shandong Province were used as research objects.Using amplicon high-throughput sequencing and fluorescent quantitative PCR(q PCR)technology,combined with the analysis of the physicochemical properties of ZS,the soil physicochemical background of PCS was clarified.The abundances of bacteria and pathogenic Streptomyces in the soil of PCS,and the structure and function of bacterial communities in the GS and ZS of PCS in different regions were explored.The biocontrol strains of PCS were screened and their biocontrol effects were initially evaluated.The main results are as follows:(1)The abundances of the pathogenic toxin txt AB gene and bacterial 16 S r RNA gene in GS in different regions of Shandong were related to the scab severity.The abundances of the pathogenic toxin gene txt AB and the bacterial 16 S r RNA gene in GS＿H in JD,TZ,and TX regions were higher than GS＿L.The abundance of the toxin gene txt AB in JD and TX regions was significantly different between GS＿H and GS＿L,and the bacterial 16 S r RNA gene abundance in the four regions was significantly different between GS＿H and GS＿L.(2)The bacterial community diversity in GS in different regions of Shandong was related to the scab severity.Alpha diversity analysis results showed that the number of OTUs in the GS＿L group in the JD,TZ,and TX regions was significantly higher than the GS＿H group,and the ZS group was only higher in the L group than the H group.The Shannon indices in the JD,TZ and TX regions were significantly different between the GS＿H group and the GS＿L group,and the ZS group had significant differences only in the JD region.The results of Beta diversity analysis showed that soil type and disease severity were the most significant factors affecting the diversity of soil microbial communities.(3)The bacterial community structure of the GS in different regions of Shandong was related to scab severity.5 OTUs were significantly enriched in GS＿H group in the four regions,including OTU6(Agrobacterium),OTU124(Methylophilus),OTU47(Sphingobium),etc.7OTUs were significantly enriched in GS＿L group in the four regions,including OTU598(Saccharimonadales),OTU1260(Gemmataceae),OTU2430(Frankiales),etc.None of the ZS group had significantly enriched OTUs together.The Random Forest analysis showed that Agrobacterium,Methylophilus,Sphingobacterium,Micromonospora,and Variovorax could be used as indicator species for PCS.(4)The bacterial community function in GS in different areas of Shandong was related to the scab severity.Membrane transport,cell growth and death,cell activity,signal transduction,and other amino acid metabolism were significantly enriched in the GS＿H group,the metabolism of terpenes and polyketones,the interaction of signal molecules,the biosynthesis and metabolism of sugars,other secondary metabolism biosynthesis and folding,classification and degradation,carbohydrate metabolism,replication and repair,transcription,translation,biodegradation and metabolism were significantly enriched in the GS＿L group.(5)The ZS microbiome of PCS in different areas of Shandong was closely related to the soil physicochemical background.The p H of ZS was significantly negatively correlated with the abundance of toxin gene txt AB and bacterial abundance.The organic matter,water content,electrical conductivity,nitrate nitrogen,total nitrogen,and total phosphorus in ZS were significantly positively and/or negatively related to the alpha diversity index of soil bacterial communities.Acidothermus and Bradyrhizobium in the GS＿H group were positively related to most bacterial groups,and Streptomyces in the GS＿L group were positively related to Micromonospora.(6)Bacillus velezensis and Arthrobacter humicola might have control effects on PCS.A total of 24 strains were isolated from the ZS＿L group,and 5 Bacillus strains were significantly antagonistic.The results of the pot inoculation test showed that the incidence rate of the Streptomyces scabies treatment group was 92.31%.The incidence rate of the the Bacillus velezensis treatment group was 61.54%,and the biocontrol rate was 33.33%.The incidence rate of the Arthrobacter humicola treatment group was 52.94%,and the biocontrol rate was 42.65%.In summary,the toxin gene abundance and bacterial abundance of GS＿L in different regions were lower in Shandong.The scab severity in different areas of Shandong was related to the diversity,species composition and function of bacterial communities in GS.The microbiome of ZS in different regions was closely related to ZS physicochemical indicators.Agrobacterium,Methylophilus,Sphingobacterium,and Variovorax could be used as indicator species of PCS.Bacillus velezensis and Arthrobacter humicola might have a protective effect on the occurrence of PCS.