Growth-promoting Effect Of Microbial Inoculants On Maize Seedlings Under Saline-alkali Stress

Soil salinization is the main problem that restricts the development of agriculture in our country,so the treatment and utilization of saline-alkali land has gradually become a research hotspot.Studies have shown that microbial inoculants derived from plant growth-promoting rhizobacteria（PGPR）play an important role in the improvement and utilization of saline-alkali land.This study screened the strain combinations through strain antagonism test and co-cultivation combination method,and clarified the growth-promoting effect of microbial inoculants on maize seedlings under saline-alkali stress through pot experiments.The main research results are as follows.（1）Four strain combinations of 35W6-6L11,35W8-6L11,6CW15-6L11 and 35W8-6CW15 were screened by strain antagonism test and co-cultivation combination method.The saline-alkali resistance of single bacteria and strain combinations in the combination were measured.It was found that all of them could grow well in saline-alkali medium(LB liquid medium with 130 mmol·L^-1salt concentration),and the combined bacterial strains were identified as 35W6-6L11,35W8-6L11,6CW15-6L11 and 35W8-6CW15.（2）The expression levels of siderophore synthesis gene of strain 6L11 and strain 6WW6were detected by fluorescence quantitative PCR under saline-alkali and LB culture conditions.The results showed that the expression levels of siderophore synthesis gene LLJ08＿RS02835of strain 6L11 were up-regulated by 1.4 times compared with the control group during the logarithmic growth phase of strain 6L11.When the growth of the strain approached the stable stage,the expression level was increased 2.1 times compared with the control group.The expression levels of siderophilic synthesis genes J9319＿RS05380 and J9319＿RS05365 in strain 6WW6 were increased by 7.0 and 11.1 times,respectively,when the growth of strain6WW6 was nearly stable.This indicates that strain 6L11 and strain 6WW6 can produce more siderophores under saline-alkali conditions.（3）The results of pot experiments showed that applying single bacterial agent and compound bacterial agent can alleviate the saline-alkali stress and promote the growth of maize seedlings.Compared with the control group,the biomass of maize seedlings increased to varying degrees,with a significant effect on ground fresh weight.C2（35W8）,C3（6CW15）,C4（6L11）and C7（6CW15-6L11）,C8（35W8-6CW15）achieved significant differences（P<0.05）,increasing 16.7%,19.1%,19.5%,18.6%,17.5%,respectively.Compared with the control group,the superoxide dismutase content of maize leaves increased by 1.6%to 25.8%.The soil catalase,sucrase and protease activity of maize seedlings rhizosphere were also improved to varying degrees,among which the sucrase activity was significantly improved.（4）The analysis of soil community structure in the rhizosphere of the maize plant.Proteobacteria,Aciobacterium,Ascomycota,and Basidiomycetes are core strains of maize rhizosphere soil samples.The analysis showed that C2（35W8）,C3（6CW15）,C4（6L11）,C7（6CW15-6L11）,and C8（35W8-6CW15）had increased bacterial Simpson,Chao1,Shannon and ACE index compared with the control group.The C7 fungal Simpson index,ACE index and Shannon index increased in the compound bacterial agent treated group compared with the control group.（5）Through principal component analysis,it was known that C4（6L11）was best in the single bacterial agent treatment group,followed by C3（6CW15）.In the compound bacterial agent treatment group,C7 treatment group（6CW15-6L11）and C8 treatment group（35W8-6CW15）had a prominent promoting effect.In conclusion,the growth-promoting effect of a single bacterial agent is better than that of the compound bacterial agent.