Plant Growth Promoting Rhizobacteria (PGPR)

In order to make rice cultivation sustainable and less dependent on phosphate fertilizers, the use of phosphate solubilizing bacteria (PSB) exhibiting other beneficial traits is a promising alternative that can contribute to rice growth improvement. With the aim to develop biofertilizer, a total of 283 bacteria belonging to Pseudomonas were isolated from the rice rhizosphere of which 67.14% was capable of solubilizing tricalcium phosphate (TCP). Based on diameter of solubilization halos (diameter ≥ 0.4 cm), 73 strains were selected and evaluated for hydrogen cyanide production. Nine bacteria were chosen to be explored for more activities. All isolates were siderophores producers but none was able to fix nitrogen. Only two bacteria, PE76 and PE77, were positive for the 1-aminocyclopropane-1-carboxylate deaminase activity. Amounts of indole acetic acid produced by test bacteria ranged between 0.68 and 20.46 mg l-1. They were also checked too for quantitative assay of TCP solubilization and thus, phosphorus concentrations were between 70.98 and 608.28 mg l-1. Four bacteria were selected for rice inoculation substituting soluble P by TCP. Significant increases in plant length and dry matter were obtained with two strains PP22 and PG1 after 30 days under controlled conditions. This stimulation is possibly not the sole result of increasing phosphate availability in the medium. Because these two efficient strains produced IAA in high concentrations in comparison with bacteria PE77 and PE76, which may partly explain the observed increases. However, more evaluation of PP22 and PG1 under field conditions is needed before recommending them as biofertilizers

The aim of this study is to assess the effects of some Plant Growth Promoting Rhizobacteria (PGPR) strains on arbuscular mycorrhization and growth of KT22’s peanut variety grown in Northwest of Morocco. The germinated seeds were inoculated with5 bacterial strains (PP22, GP70, GR1, PR29 and GR70). Peanut plants were then grown in plastic pots in 2 unsterilized soils collected from subsistence farmers’ fields of Laaouamra and Moulay Bouselham. Plant harvesting was made after 8 weeks of growth under chamber conditions. Results showed the positive and negative effects of these rhizobacteria on growth, mycorrhization and nodulation of peanut. Likewise, the origin of soils influenced the response of inoculated plants to bacterial strains. Highest stimulation was obtained with PP22 and GP70 that increased significantly the mycorrhizal colonization, nodulation, mineral nutrition (N, P and K) and leaf area in both soils. Also, PR29 improved leaf area, shoot length and mineral nutrition. On the other hand, GR70 reduced mycorrhizal infection and plant growth, especially on Moulay Bouselham’s soil. This study reveals that GP70 and PP22 could be identified as Mycorrhiza Helper Bacteria (MHB). They can enhance growth, yield and nutrient uptake in combination with native rhizobia and arbuscular mycorrhizal fungi (AMF).

production has captured the interest of agronomists for a long time. With the aim to select beneficial bacteria exhibiting several plant growth promoting (PGP) traits, 44 bacteria were isolated from the rhizosphere of the legume Lupinus hirsutus L., and tested for solubilization of tricalcium phosphate (Ca3 (PO4)2). Of 35 phosphate solubilizing rhizobacteria, 14 isolates were selected for their solubilization diameters (0.6-1cm). Four bacteria were able to produce indole acetic acid (IAA), while none was positive for hydrocyanic acid (HCN). Other PGP traits (siderophores production, Atmospheric nitrogen fixation and ACC deaminase) were searched for these 4 bacteria. Except the isolate RL5 strain which showed ACC deaminase activity, all strains were unable to produce siderophores or to fixe nitrogen. Phosphorus solubilizing ability of these 4 strains was tested in liquid medium with 0.5% Ca3(PO4)2, and the values of soluble P were ranged between 81.94 and 298.66 mg / l after 7 days of incubation, obtained respectively by RL77 and RL10. This bacterial solubilization of P was accompanied by a fall in pH to pH 4.83 in presence of RL10. These isolates were shown to belong to the genus Enterobacter. The rice inoculation test (Puntal variety) was performed in pots substituting soluble P by Ca3 (PO4)2. Significant increases were obtained for shoot length and dry weight of plants in presence of RL5, RL10 and RL16, as compared to the control. However, RL77 showed a significant decrease of the different parameters.

The plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) represent the two main beneficial biofertilizers for agroecological plant growth. Our work is to assess the impact of some bacteria, estimated as PGPR, in interaction with native mycorrhizal fungi on development and growth of peanuts cultivated in the northwest of Morocco. In this framework, the diversity and richness of soil by AMF was assessed by direct counting and morphological identification of spores. The seeds germinated peanuts are inoculated by four bacterial strains: GP70, PT66, ET76 and GT70. After one month of growth, the plant biomass and mycorrhizal parameters were evaluated. The number of AM fungal spores detected in field-collected soils was relatively high. The morphological characters indicated that the spore populations consisted of six morphotypes, of which five main genus have been identified: Acaulospora, Scutellospora, Rhizophagus, Septoglomus and Glomus. Microscopic observations of stained roots showed a significant increase in mycorrhizal and arbuscular intensity for plants inoculated with GP70, PT66 and ET76. However, only inoculation with GP70 promoted a significant increase in aerial dry biomass (ADB) of peanut. Inoculation of plants by GT70 has favored the development of nematodes in root. This phytoparasitic infection is accompanied by an increase in the dry root biomass and a significant reduction in the ADB. The improvement in ADB for plants inoculated with GP70, can be explained by a good synergy between this bacterial strain, native AMF and host

The ability to produce indole acetic acid (IAA) by endophytic bacteria is one of the basic criteria for the use of bacteria as plant growth promoter agentwhich is essential for the agricultural production. The objectives of this study were to evaluate the ability of 17 bacterial isolates to produce IAA and its effect on improvement of rice seed germination and molecular identification of the selected isolates based
on the 16S rRNA gene. The IAAcontentwas determined using Salkowski method measured by spectrophotometer UV-Vis and the effect of endophytic bacteria inoculation on seed germinationwas done by in vitro assay. Sequences of the selected isolates 16S rRNAamplified by PCRwere analyzed the homology against bacterial 16S rRNA database in Genebank. IAA values ranged from 6.632 to 50.053 mg/L with the highest IAA production shown by isolate 6KJ which was followed by 4PB (41.807 mg/L). Bacterial IAA increased rice seed vigor significantly compared to control. However, bacterial inoculation with different concentrations of IAA did not significantly affect, the growth of rice plants. Based on the IAA and its effect on seed vigor, 6KJ, 4PB and 2KB were selected for molecular identification. Results showed that the three isolates belonged to Bacillus genus, 6KJ as B. aryabhattai, 4PB belonging to B. cibi and 2KB having 97% homology with B. marisflavi. Further evaluation of the selected endophytic isolates producing IAA is necessary to be carried out to explore their potency as a source of hormone to promote plant growth.
Keywords: indole acetic acid, endophytic bacteria, rice, vigor.

Widnyana, I. K., Sumantra, I. K., Pandawani, N. P., & Eka Pasmidi Ariati, P. (2019) Induction of total phenol and salicylic acid with Pseudomonas spp. suspension as indications increasing systemic resistance on vanilla plant. Bulgarian Journal of Agricultural Science, 25(3), 000-000 This study aims to determine the effect of Pseudomonas spp. in inducing the resistance of vanilla plants characterized by increasing total phenol content and salicylic acid in vanilla plant tissue after inoculation with Pseudomonas spp. suspension. In this study, vanilla cuttings were inoculated with Pseudomonas spp. suspension with a population density of 5 x10 6 CFU applied by root immersion, injection of the stem, and injection of vanilla leaves. The results showed that there was an increase of total phenol and salicylic acid content in vanilla plant tissue. The highest total phenol content was found in the Pseudomonas spp. W80 suspension treatment, which averaged 260.27 mg/g or an increase 106.89% compared to the distillated water treatment as control. The total phenol content average in the 2.6.D (2.6-dichloro-isonicotinic acid (INA) treatment is 240.80 mg/g or an increase of 91.41% compared to control. The highest salicylic acid content found in the treatment of Pseudomonas spp. W02 suspension is 37.65 ppm or 72.94% increase compared to control, followed by 2.6.D treatment of 32.55 ppm or 49.52% increase compared to control. Bacteria Pseudomonas spp. W02, W68, and W80 isolates has the ability to induce vanilla plant resistance with different abilities

Plants are continuously exposed to a wide array of environmental stresses. Abiotic stress is one of the foremost limiting factors that are responsible for low agricultural productivity. The incidence of extreme events like prolonged drought, salinity, heavy rain and flooding, heatwave, and frost damage, metal toxicities in problematic soils are increasing day by day under the scenario of changing climate. Crop plants need to acclimatize against adverse external pressure created by environmental and edaphic conditions with their intrinsic biological mechanisms. Drought is one of the significant constraints on agricultural productivity worldwide and is likely to increase further. Several adaptations and mitigation strategies are required to cope with drought stress. Here, microorganisms can come to the rescue in an economical and eco-friendly manner to help plants for better fitness against abiotic stressors. Their interactions with compatible microbes evoke various kinds of local and systemic responses that improve the plant's metabolic capability to fight against abiotic stresses. Root-associated bacterial communities play a vital role in maintaining the health of the plant host. Therefore, it is essential to understand better the mechanisms that influence microbial communities composition and structure and what role the host may play in the recruitment and control of its microbiome. Plant growth-promoting rhizobacteria (PGPR) could play a significant role in alleviating drought stress in plants. These beneficial microorganisms colonize the rhizosphere/endo-rhizosphere of plants and impart drought tolerance by producing exopolysaccharides (EPS), phytohormones, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, volatile compounds, inducing accumulation of osmolytes, antioxidants, upregulation or downregulation of stress-responsive genes, and alteration in root morphology in the acquisition of drought tolerance. In the present review, we elaborate on the role of PGPR and various mechanisms, which in turn helping plants to cope with drought stress.

The inoculation of plant growth-promoting rhizobacteria in agricultural interest crops such as maize constitutes an economically and environmentally friendly alternative to chemical fertilization. Stenotrophomonas is a common bacterial genus in many soil types and rhizospheres of different crops, and presents mechanisms for growth promotion such as biological nitrogen fixation, mineral solubilization and phytohormones production. Consequently, the present work aimed to characterize and molecularly identify Stenotrophomonas strains from the maize rhizosphere. For this, an isolation was performed from rhizospheric and rhizoplane soil and colonies with cultural characteristics similar to those described for this genus were selected. The microscopic characteristics and the ability to perform the biological nitrogen fixation solubilize different phosphate and potassium sources and the antagonistic activity against Fusarium oxysporum were also taken into account. Molecular identification ...