Growth Promoting Characteristics of Bacillus amyloliquefaciens GZA69 and Its Biocontrol Potential Against Soft Rot of Amorphophallus konjac

Abstract

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria colonizing the plant rhizosphere and can promote plant growth. PGPR have important application potential in the field of microbial fertilizers. This study isolated and characterized a PGPR strain GZA69 from konjac rhizosphere soil collected from Damogu Village, Luliang County, Qujing City, Yunnan Province, China. The strain was identified as Bacillus amyloliquefaciens. GZA69 showed diverse plant growth-promoting abilities, including nitrogen fixation, phosphorus solubilization, siderophore production, and indole-3-acetic acid (IAA) production. Tomato was used as an indicator crop to evaluate its growth-promoting effect, two GZA69 suspension concentrations (A1, OD600 = 0.3 and A2, 0.6) were used to treat tomato seeds and seedlings. Plate confrontation assay and konjac corm tissue inoculation were conducted to identify the antagonistic effect of GZA69 strain on the pathogen of konjac soft rot disease. The results showed that, both GZA69 concentrations significantly promoted tomato seed germination (A) and seedling growth, with growth increased of 8.2% and 9.66% in height, 20.87% and 22.77% in root length, and 90% and 130% in fresh weight, respectively. Additionally, GZA69 demonstrated a significant inhibitory effect on the konjac soft rot pathogen, with an inhibition zone of 1.47±0.07 cm. Furthermore, GZA69 effectively reduced disease incidence in inoculated corm tissues, with disease index decreased by 8.00%, 16.23%, 24.80% in co-inoculated with different concentrations of GZA69 suspensions (solution of soft rot pathogen and GZA69 bacterial at ratios of 1:1, 1:2, and 1:3, respectively) comparted to the control (sterile water). In summary, the B. amyloliquefaciens GZA69 screened from konjac rhizosphere soil has various plant growth promoting characteristics and has the potential to prevent and control konjac soft rot disease, which has important application value for developing konjac microbial fertilizers.