The effect of endophytic bacteria on the growth, medicinal quality, and rhizosphere soil environment of Isatis indigotica Fort

Plant growth-promoting endophytes (PGPE) can form a mutually beneficial symbiotic relationship with host plants, analyzing the ability of endophytic bacteria of Isatis indigotica to promote growth and improve the rhizosphere environment and exploring the influence of dominant endophytic bacteria on the structure of rhizosphere microbial communities. In this study, we evaluated the ability of the three endophytic bacteria strains by a field experiment. The single endophytic bacterial strain and combination of every two bacterial strains were used for irrigating the rhizosphere of I. indigotica four times, and related indicators and rhizosphere soil of I. indigotica were measured. We screened out the dominant treatment groups based on the total active biomass of I. indigotica and analyzed microbial diversity of rhizosphere soil in dominant treatment groups. The results showed that endophyte treatments had significant effects on growth and physiology of I. indigotica , in which T11–28 and BC00 had the most significant effect on the dry weight of the aboveground part and underground part, respectively. The endophyte treatments had different effects on the content of active ingredients, rhizosphere soil chemical properties, and enzyme activities of I. indigotica , with BC00 promoting indigo and indirubin in leaves most significantly and BV11 promoting epigoitrin in roots most effectively. Total active biomass was calculated as the product of active ingredient content and biomass per plant. Based on this parameter, BC00 was the dominant treatment group, and the analysis of the diversity of its rhizosphere soil flora revealed that BC00 was able to enrich Methylobacillus , Alternaria , and other plant-growth-friendly flora. In the comprehensive analysis, the treatments of three endophytic bacterial strains of I. indigotica had significant promotion effects on its growth physiology and active ingredients and had obvious improvement effects on the rhizosphere environment, among which BC00 had the best comprehensive effect, which was associated with alterations in the rhizosphere soil microbial community structure.