The rhizosphere of the pioneer plant Dicranopteris dichotoma (Thunb.) Bernh. contains powerful and robust rhizosphere growth-promoting bacteria

Figures & data

Figure 1. Plant growth promotion characteristics of isolated rhizobacteria in vitro. (A) Isolate samples showing cellulase production; (B) Isolate samples showing siderophore production; (C) Isolate samples showing phosphate solubilization. A clear halo around the bacterial colony indicates positive results; (D) In vitro colorimetric determination of IAA and indole compounds in bacterial supernatants. A pink color indicates positive reaction; (E) Phosphorus standard curve; (F) Phosphorus soluble content and pH value of four strains; (G) Determination of siderophore in bacterial supernatant. The pink color of the solution indicates that the siderophore content is higher, and the blue color is the opposite.

Table 1. Results of plant growth promotion activity test of bacterial isolates.

Isolate No.	P growth	PSI	Indole acetic acid (IAA) production	Siderophore production	CMC EI
MQB1	√	1.11 ± 0.02	94.32 mg/L	95.9%	–
MQB2	√	1.37 ± 0.3	89.53 mg/L	97.1%	–
MQB3	√	1.24 ± 0.09	44.33 mg/L	66.8%	–
MQB4	√	1.27 ± 0.2	3.73 mg/L	87.4%	–
MQB5	√	1.2 ± 0.05	13.82 mg/L	67.9%	2.67 ± 0.11
MQB6	√	1.21 ± 0.04	44.93 mg/L	–	–
MQB7	√	1.64 ± 0.11	134.46 mg/L	7.8%	1.58 ± 0.04
MQB8	√	1.95 ± 0.13	44.73 mg/L	9.5%	–
MQB9	√	1.36 ± 0.06	0.73 mg/L	87.8%	–
MQB10	√	1.84 ± 0.05	23.06 mg/L	78.7%	2.22 ± 0.08
MQB11	√	2.19 ± 0.28	4.93 mg/L	69%	–
MQB12	√	1.5 ± 0.12	49.19 mg/L	60.7%	1.70 ± 0.05
MQB13	√	1.65 ± 0.18	1.33 mg/L	85.9%	–
MQB14	√	1.21 ± 0.05	3.73 mg/L	76.7%	–
MQB15	√	1.18 ± 0.04	3.99 mg/L	73.6%	–
MQB16	√	1.11 ± 0.02	7.33 mg/L	64.7%	–
MQB17	√	1.37 ± 0.3	9.73 mg/L	82.8%	–
MQB18	–	–	0.37 mg/L	–	–
MQB19	–	–	2.76 mg/L	–	–
MQB20	–	–	8.22 mg/L	–	–
MQB21	–	–	2.89 mg/L	–	–

Note: ‘√’ indicates that the isolate can grow in inorganic phosphorus medium; ‘-’ indicates no function.

Figure 2. Neighbor-joining phylogenetic analysis originating from the multiple alignments of 16S rRNA gene sequence of PGPR strains with those of other closely related strains existing in the GenBank database.

Table 2. Molecular identification of rhizobacteria based on 16S rRNA gene sequences.

Isolate No.	Genbank accession No.	Closest BLAST matches (accession No.)	Classification of matched species	% Identity
MQB 5	OR226568	KY621526.1 KY416926.1	Bacillus pumilus Bacillus altitudinis	99.93% 99.93%
MQB 7	OR226569	CP046722.1 CP002206.1	Pantoea agglomerans Pantoea vagans	99.73% 99.73%
MQB 10	OR226570	CP041691.1 CP033576.1 MG727662.1	Bacillus amyloliquefaciens Bacillus velezensis Bacillus subtilis	99.65% 99.65% 99.65%
MQB 12	OR226572	KX230137.1 JF683607.1	Priestia aryabhattai Priestia megaterium	100.00% 100.00%

Figure 3. Growth-promotion effects of the obtained strains MQB5、7、10、12 on V. radiata seedlings after cocultivation for 30 days (A), CK was irrigated with sterile water. The effects of PGPR strains MQB5, 7, 10, and MQB12 on the V. radiata seedlings shoot fresh weight (B), shoot dry weight (C), root fresh weight (D), root dry weight (E), stem length (F), first-order lateral root (G), leaf number (H), root length (I). Different letters (a-c) inducate statistically significant differences between each treatment vs the control (CK) group (p < 0.05), and the significance was determined via ANOVA.

Availability of data

The data that support the findings reported in this study are available from the corresponding author [YW] upon reasonable request.