The novel Pseudomonas thivervalensis strain JI6 promotes growth and controls rusty root rot disease in Panax ginseng

The bacterial strain JI6, which has plant growth-promoting characteristics, was isolated from ginseng rhizosphere soil. It can produce indoleacetic acid (IAA), dissolve phosphorus, dissolve potassium and fix nitrogen and significantly promoted the growth of ginseng. The strain was identified as Pseudomonas thivervalensis by morphological, physiological and biochemical characteristics and 16S rDNA sequence analysis. The bud length of ginseng seeds treated with 10⁹ CFU/mL JI6 suspension increased significantly by 42.76 % after 15 days. The fresh weight and the ginsenoside content of 3-year-old ginseng roots significantly increased by 38.72 % and 24.20 %, respectively with the 10⁸ CFU/mL JI6 suspension for five months in the field. The strain JI6 can inhibit the six fungal pathogens and control rusty root rot of ginseng. For the biocontrol mechanism, the strain JI6 can colonize in ginseng rhizosphere soil. After treatment with JI6, the activitie of five ginseng defence enzymes of β-1.3 glucanase, peroxidase and phenylalanine ammonia-lyase, chitinase and superoxide dismutase and four soil enzymes of urease, phosphatase, invertase, and catalase significantly increased. The effect of strain JI6 on soil microbial community showed that the microbial diversity increased and the abundance of beneficial microorganisms elevated, while the abundance of pathogenic microorganisms decreased. This study indicate the great potential of P. thivervalensis JI6 for use as a biological agent for the control of ginseng rusty root rot.