Table 2.
Characteristic features of Plant Growth-Promoting Rhizobacteria (PGPR) used in the study
| Species | Strain (host plant) | Colonisation level of roots (Log10 UFC mg−1 fresh root)a | Detection in surface-sterilized rootsb | Nitrogenase activityc (nmol C2H4 mg proteins−1 h−1) | Indole acetic acidd (µg mL−1 A−1600) | Indole lactic acidd (µg mL−1 A−1600) | Indole carboxylic acidd (µg mL−1 A−1600) | |||
|---|---|---|---|---|---|---|---|---|---|---|
| Trp− | Trp+ | Trp− | Trp+ | Trp− | Trp+ | |||||
| A. lipoferum | 4B (rice) | 3–5 | – | 1975 ± 93 | < 1 | 1.48 | ND | 13.16 | ND | 40.66 |
| B518 (rice) | 3–5 | (+) | 11,074 ± 1920 | ND | 1.50 | ND | ND | ND | 2.37 | |
| TVV3 (rice) | 3–5 | – | 3074 ± 58 | ND | 1.76 | ND | ND | ND | 21.89 | |
| Sp59b (wheat) | 3–5 | (+) | 824 ± 102 | ND | < 1 | ND | 158.09 | ND | ND | |
| Br17 (maize) | 3–5 | (+) | 3849 ± 70 | < 1 | 7.96 | ND | 5.94 | ND | 30.90 | |
| Azospirillum sp. | B510 (rice) | 3–5 | + | 10,763 ± 877 | ND | ND | ND | ND | ND | 1.64 |
| A. brasilense | Sp245 (wheat) | 3–5 | (+) | 2035 ± 160 | < 1 | 3.73 | ND | 2.46 | ND | 6.01 |
| A. zeae | N7 (maize) | 3–5 | + | 4397 ± 272 | ND | ND | ND | 1.69 | ND | < 1 |
| P. phytofirmans | PsJN (onion) | > 6 | – | NT | ND | ND | ND | ND | ND | 32.50 |
| H. seropedicae | SmR1 (sorghum) | > 6 | (+) | 575 ± 60 | ND | 1.48 | ND | 498.11 | ND | 1.21 |
aData retrieved from (Valette et al. 2020)
b−, a strain not retrieved inside roots in any of the experiments; (+), a strain retrieved from root tissue in at least one experiment, but not in all; +, a strain retrieved from root tissues in all experiments
cValues of nitrogenase activity represent the means of three independent repetitions with standard deviation. NT: not tested as PsJN lacks nitrogenase genes
dUsing standard curves, the quantity of these compounds was determined per mL of culture and for inter-strain comparison the quantity was expressed per unit of absorbance at 600 nm. Values represent the means of two independent repetitions. ND: not detected