Effects Of Rhizosphere Growth-Promoting Bacteria On Pepper Growth And Rhizosphere Microbial Community

Pepper(Capsicum annuum L.)is an important facility vegetable crop,but the deterioration of the soil environment and pests and diseases have severely restricted the production of pepper.Studies have shown that plant rhizosphere growth promoting bacteria(PGPR)can effectively promote crop growth and increase crop resistance.However,the same PGPR strain often has different growth-promoting effects on different varieties of pepper,and the reason is not very clear.Indigenous microorganisms in the rhizosphere of plants are important factors that affect the survival and function of exogenous PGPR.At the same time,plants can actively recruit PGPR through root exudates.This study first screened out a strain that has a growth-promoting effect on pepper;then,through high-throughput sequencing,analyzed the effect of this strain on the pepper rhizosphere microbial community;finally,analyzed the colonization of this strain in the rhizosphere of different varieties of pepper Differences,as well as the content of organic acids secreted from the roots of different pepper varieties and the expression of related genes,to explore the reasons for the differences in the colonization of PGPR in the rhizosphere of different pepper varieties.The main results obtained are as follows:(1)Through pot experiments,the Bacillus P1 strains with better growth-promoting effects on XYJ and LMZ peppers were selected from 4 strains of Bacillus and 1 strain of Pseudomonas.(2)Illumina Mi Seq sequencing was used to analyze the effect of root watering P1 strain on XYJ and LMZ pepper rhizosphere soil microbial communities.It was found that the P1 strain changed the structure and composition of the bacterial and fungal communities in the rhizosphere soil of two varieties of pepper.Compared with the uninoculated group,the main OTUs that were significantly enriched in pepper rhizosphere after P1 strain treatment were: Bacillus,Flavobacterium,Fluviicola,norank Sericytochromatia,Lysobacter,norank Solimonadaceae and Fontimonas spp.out,and Unclassified Fungi.(3)Through pot experiment,the growth-promoting effect of P1 strain on different varieties of pepper was analyzed.The P1 strain was found to promote the growth of CQ118 and HN2 peppers,but did not promote the growth of HN4 and FY3 peppers.The rhizosphere condition of the above four pepper varieties grown by P1 strain grown in sterilized soil was analyzed by spreading plate method,and it was found that P1 strain has more rhizosphere of pepper varieties that can play a role in promoting growth.(4)The contents of oxalic acid,malic acid,citric acid,succinic acid and fumaric acid in the root exudates of four varieties of pepper were detected by HPLC.It was found that the contents of organic acids secreted by the roots of different varieties of pepper are different.Among them,CQ118 has the highest organic acid content in the root exudates and FY3 has the lowest content.The q PCR results showed that the higher the content of malic acid in the root secretion,the higher the relative expression of ALMT gene in pepper varieties.(5)Illumina Mi Seq sequencing was used to analyze the effect of root watering P1 strain on the rhizosphere soil microbial community of five different pepper varieties.After inoculation,the bacterial community structure in the rhizosphere soil of each variety of pepper was changed.At the same time,the relative abundance of pepper rhizosphere bacteria OTU4400 was significantly increased.In contrast,the relative abundance of CQ118,HN4 and HN2 rhizosphere bacteria OTU4400 was higher,while FY3 and HN4 is lower;after inoculation,the relative abundance of OTUs of different varieties of pepper rhizosphere bacteria is different.FY3 and HN4 peppers with weaker recruitment ability partially enriched OTU belong to Actinobacteriota,and partly reduce OTU belongs to Verrucomicrobiota;Q3and HN2 peppers with strong recruiting ability partially enriched OTUs belong to Sumerlaeota and Cyanobacteria,and CQ118 and HN2 peppers partially enriched OTUs belong to Acidobacteria.In summary,this experiment screened out the Bacillus P1 strain with better growth-promoting effects on peppers.Inoculation with the P1 strain can change the structure and composition of XYJ and LMZ pepper rhizosphere soil bacteria and fungi communities.It was found that the rhizosphere colonization ability of strain P1 affected the growth-promoting effect of strain P1 on different varieties of pepper,and its colonization ability may be related to the organic acid components in pepper root exudates.Community structure and composition have different effects.