Plant growth-promoting rhizobacteria (PGPR) isolated from the rhizosphere soil of eight field crops at different locations in Egypt were identified. Rhizobacteria strains were identified as Bacillus endophyticus AW1 5, B. filamentosus EM9, ET3, Micrococcus luteus KT2, FW9, FC13, SaW4, Enterobacter cloacae SK18, Pseudomonas azotoformans TPo10, Citrobacter braakii TC3. All isolates solubilised insoluble phosphate and produced IAA, while only six were able to produce siderophores in vitro. Vegetative growth and yield of wheat cv. ‘Sakha 94’ were enhanced after the application of single inoculation of each isolate compared to the control. Grain yield was increased by 20.7– 96.5% over the control according to bacterial isolates. Available phosphorus (P) and counts of total bacteria in soil were observed to be significantly increased in treatments than in control. After the wheat harvest, soil pH was observed to be decreased, and a highly significant negative correlation was observed between soil pH and the levels of available phosphorus. Significant increases in grain and straw yields, as well as uptake of nitrogen (N) and P by plants, were observed due to inoculation with PGPR isolates. Levels of photosynthetic pigments, free amino acids, free phenolics, and reducing sugars in flag leaf and spikes were significantly enhanced by the application of all PGPR isolates compared to the control. Thus this study identifies the PGPR isolates for the improvement of the growth, yield, and quality of wheat. The study may be also useful for field evaluation under different soils and environmental conditions before generalising PGPR isolates as biofertilisers.

Taro leaf blight caused by Phytophthora colocasiae affects plant health and is a major threat to taro culture in Cameroon. Chemical fertilizers used often harm the ecosystem. Plant growth-promoting rhizobacteria (PGPR) are better alternatives that increase plant growth promotion and suppress phytopathogens. In the present study, a total of 67 fluorescent Pseudomonas spp. was characterized by 17.91, 5.97, and 4.47% populations of P. fluorescens, P. chlororaphis, and P. putida, respectively, among the most represented. More than 36% of bacteria showed antagonistic potential through the production of both diffusible and volatile compounds. Some of them (03) exhibited antagonistic activity in dual culture against P. colocasiae with a diameter greater than 13 mm. These rhizobacteria produced a significant amount of siderophore, IAA, SA, HCN, protease, lipases, and cellulases. For the pot experiment, treatment by Pseudomonas significantly increased the enzymatic activity involved in the resistance of taro, such as peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL). The two antagonists also increased plant growth parameters of taro such as chlorophyll, plant height, shoot length, total leaf surface, fresh root biomass, and fresh leaf biomass. These findings showed that fluorescent Pseudomonas have an intriguing and undeniable potential in the fight against P. colocasiae, which could lead to the development of a biopesticide in the future.

The use of local bacteria is preferred in bioleaching as an environmental-friendly alternative technology in gold mining. In a preliminary study, rhizobacteria were isolated and cultured from three types of hyperaccumulator vegetation from the Ratatotok gold mine, Indonesia, namely Pteris vittata L., Syzygium aromaticum L., and Swietenia mahagoni Jacq. These rhizobacteria still need to be characterised and identified. This study is aimed to cover bacterial phenotypic characterisation, assessment of bacteria resistance to tailing, and identification of bacterial strains the exhibit the highest resistance to tailings. The assessment was carried out across a spectrum of tailing concentrations, selecting the three most robust strains for molecular identification. The process involved genotypic characterisation to determine the species name by analysing the 16S rRNA gene. The results reveal that the phenotypic characteristics of the bacteria isolates vary, but all of them are the indole acetic acid (IAA) hormone producers. The highest IAA producer is the isolate from the rhizosphere of S. aromaticum. Based on the genotypic characterisation test, three most resistant isolates to tailing stress are the following strains Pseudomonas aeruginosa (RTKP1) and Stenotrophomonas geniculata (RTKP2), both from the rhizosphere of P. vittata; as well as Bacillus cereus (RTKS) from the rhizosphere of S. aromaticum. These three strains need to be further tested for their bioleaching capability to recover gold from tailings. Additionally, this study recommends that gold recovery using biological agents can combine the role of hyperaccumulator plants in phytomining and rhizobacteria in bioleaching.

In this study, the effect of six commercial biocontrol strains, Bacillus pumilus INR7, B. megaterium P2, B. subtilis GB03, B. subtilis S, B. subtilis AS and B. subtilis BS and four indigenous strains Achromobacter sp. B124, Pseudomonas geniculate B19, Serratia marcescens B29 and B. simplex B21 and two plant defense inducers, methyl salicylate (Me-SA) and methyl jasmonate (Me-JA) were assessed on suppression of wheat take-all disease. Treatments were applied either as soil drench or sprayed on shoots. In the soil drench method, the highest disease suppression was achieved in treatment with strains INR7, GB03, B19 and AS along with two chemical inducers. Bacillus subtilis S, as the worst treatment, suppressed take-all severity up to 56%. Both chemical inducers and bacterial strains AS and P2 exhibited the highest effect on suppression of take-all disease in the shoot spray method. Bacillus subtilis S suppressed the disease severity up to 49% and was again the worst strain. The efficacy of strains GB03 and B19 decreased significantly in the shoot spray method compared to the soil drench application method. Our results showed that most treatments had the same effect on take-all disease when they were applied as soil drench or sprayed on aerial parts. This means that induction of plant defense was the main mechanism in suppressing take-all disease by the given rhizobacteria. It also revealed that plant growth was reduced when it was treated with chemical inducers. In contrast, rhizobacteria not only suppressed the disease, but also increased plant growth.

Rice blast is one of the most destructive rice diseases known to cause considerable yield losses globally. Plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) are closely associated with rice plants and improve plant growth and health. To determine how isolated bacteria trigger rice growth, an assessment of phosphate solubilization and auxin production mechanisms was carried out in vitro and in vivo. In this study, the interactions between PGPR and Rhizophagus irregularis were evaluated in wildtype and CYCLOPS mutant plants to provide a sustainable solution against blast disease and reduce the amount of yield loss. Importantly, Bacillus subtilis UTSP40 and Pseudomonas fluorescens UTSP50 exhibited a suppressive effect on AMF colonization which shows the probable existence of a functional competition between AMF and PGPR to dominate the rhizosphere. On the other hand, R. irregularis decreased the biocontrol activity of B. subtilis UTSP40 in wild type, although this reduction was not significant in mutant plants. Results showed that the same defense-related genes were induced in the roots of wild type colonized by B. subtilis UTSP40 and R. irregularis. Therefore, plant cell programs may be shared during root colonization by these two groups of beneficial microorganisms.

The role of the tea commodity in the economy of Indonesia is quite strategic. Various types of microorganisms in nature have been known to increase the benefit of the root function, suppress disease, and accelerate plant growth. This study aimed to determine the potential of indigenous bacteria (Azoto II-1, Acinetobacter sp., bacteria Endo-5, bacteria Endo-65 and Endo-76) on the growth of tea plants and their potential in increasing resistance to blister blight disease. The test of microbes’ potential effect on growth and blister blight was conducted in Gambung, West Java in an experimental field using a randomized block design (RBD) with six treatments and each treatment was replicated four times. The composition of the treatments was: A) Endo-5; B) Endo-65; C) Endo-76; D) Azoto II-1; E) Acinetobacter sp.; and F) control (without microbes). Bacterial suspension was applied directly to the soil at a dose of 2 l · ha−1. The bacterial suspension was applied six times at 1 week intervals. The results of field observations indicated that the intensity of blister blight decreased in all treatments but did not significantly differ from the control. Meanwhile, the results of Acinetobacter sp. treatment in tea shoots was 17.26% higher than the control.

The effects of a microbial inoculant (Thervelics®: a mixture of cells of Bacillus subtilis C-3102 and carrier materials) on rice (Oryza sativa cv. Milkyprincess) and barley (Hordeum vulgare cv. Sachiho Golden) were evaluated in four pot experiments. In the first and second experiments, the dry matter production of rice and barley increased significantly by 10–20% with the inoculation of the mixture at a rate of 107 cfu ⋅ g–1 soil compared with the non-inoculated control. In the third experiment, the growth promoting effects of the mixture, the autoclaved mixture and the carrier materials were compared. The dry mater production of rice grains was the highest in the mixture, and it was significantly higher in the three treatments than in the control, suggesting that the carrier materials may also have a plant growth promoting effect and the living cells might have an additional stimulatory effect. To confirm the efficacy of the living cells in the mixture, only B. subtilis C-3102 cells were used in the fourth experiment. In addition, to estimate the mechanisms in growth promotion by B. subtilis C-3102, three B. subtilis strains with similar or different properties in the production of indole-3-acetic acid (IAA), protease and siderophore and phosphatesolubilizing ability were used as reference strains. Only B. subtilis C-3102 significantly increased the dry matter production of rice grains and the soil protease activity was consistently higher in the soil inoculated with B. subtilis C-3102 throughout the growing period. These results indicate that the microbial inoculant including live B. subtilis C-3102 may have growth promoting effects on rice and barley.

Salinity is one of the most significant constraints to crop production in dry parts of the world. This research emphasizes the beneficial effects of plant growth-promoting rhizobacterial isolates (PGPR) on the physiological responses of maize and wheat in a saline (NaCl) environment. Soil samples for the study were collected from a maize field in Baddi, Himachal Pradesh, India. Isolated bacterial strains were screened for salt (NaCl) tolerance and plant growth-promoting characters (i.e., indole acetic acid (IAA) production, siderophore production, amino cyclopropane-1-carboxylic acid (ACC) deaminase activity, hydrogen cyanide (HCN) production, and mineral phosphate solubilization). Screened bacterial isolates were further tested in pot experiments to examine their effects on wheat and maize growth. The treatments included five levels of bacterial inoculation (P0: control, P1: ACC deaminase positive + siderophore producer + NaCl tolerant bacteria, P2: mineral phosphate solubilizer + HCN producer + NaCl tolerant bacteria, P3: IAA producer + ACC deaminase positive + NaCl tolerant bacteria, P4: bacterial consortium, P5: Phosphomax commercial biofertilizer) and salt stress at 6 dS/m. Research findings found that exposure to a bacterial consortium led to the highest growth parameter in maize, including shoot length, root length, shoot and root dry weight followed by P2, P3, and P5 treatments at 6 dS/m salinity levels. However, P2 showed the best results for wheat at the same salinity levels, followed by P3, P4 and P5 treatments. P1 treatment did not show a significant result compared to control at 6dS/m salt level for both crops. The maximum proline content in maize and wheat was observed in P4 (23.28 μmol · g−1) and P2 (15.52 μmol · g−1) treatments, respectively, followed by P5 with Phosphomax biofertilizer. Therefore, the study proposed the application of growth-promoting bacterial isolates as efficient biofertilizers in the Baddi region of Himachal Pradesh, India.