Search

Rhizoremediation involves the use of plants and plant growth promoting rhizobacteria (PGPR) for remediation of contaminated soil. This study evaluated the use of Pseudomonas aeruginosa and Eleusine indica to remediate cadmium-polluted soil. Soil samples were collected around the roots of E. indica and PGPR were isolated and evaluated for their capacity for plant growth promotion. P. aeruginosa was selected for Cd remediation experiment which was based on treatments T1 (control soil), T2 (soil + cadmium), T3 (soil + plant + Cd + Pseudomonas applied 2x monthly) T4 (Soil + Plant + Cd + Pseudomonas applied once). T5 (soil + plant + Cd + Pseudomonas applied 1x monthly) T6 (soil + plant + Cd) and T7 (soil and plant). Cd concentration in soil treatments was equivalent to 8 mg/kg and treatments were monitored for 2 months. Bacterial count, physicochemical parameters, nutrient analyses, and Cd removal were subsequently evaluated. T3 had higher bacterial count and pH values (p < 0.05) relative to other treatments and this could be due to the inoculum addition. Conversely, reduction in electrical conductivity, organic carbon and organic matter observed in T3 could be attributed to improved rhizospheric activities. Again, rhizoremediation was highest (P < 0.05) in T3 (90 %) and this suggests P aeruginosa made bio-absorption of Cd easier for E. indica relative to treatments that do not have the inoculum. This study showed that E. indica together with P. aeruginosa are suitable candidates for phytoremediation of Cd contaminated soils.

Salinity is a major environmental stress that limits crop production worldwide. It is well-understood that environmental adaptations, physiological and biochemical traits adjust salinity tolerance in plants, but imparting the knowledge gained towards crop improvement remain arduous. Utilizing the potentially of beneficial microorganisms present in the rhizosphere is an alternative strategy to improve crop production under optimal or stress conditions. The current study aims at examining the ability of plant growth-promoting rhizobacteria (PGPR) in improving coriander growth under salt stress condition. Coriander seeds were inoculated via dual culture of Azospirillum brasiliense and Azotobacter chroococcum, and therefore subjected to four levels of salt stress (0, 40, 80 and 120 mM NaCl) with three replications in a research greenhouse. Seventy-five days after sowing, when leaves fully developed, leaf samples were collected and the traits were measured. The results indicated that the dual inoculation improved chlorophyll a and b content, in comparison to the un-inoculated plants. The dual inoculation increased grain yield, stem fresh and dry weights by 11.6, 11.3 and 17.2%, respectively; it also enhanced total plant fresh and dry weights by 6.1 and 10.2%, respectively, as compared to control. As a result, the dual inoculation significantly improved catalase (CAT), but decreased ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) enzymes activities, as compared to control plants. Salt stress significantly increased (CAT) activity in the leaves, whereas it resulted in significant reduction in (APX) and (GPX) activity, especially in inoculated plants. Furthermore, dual inoculation decreased Na and subsequently increased K concentration in coriander leaves comparing with untreated plants. Overall, these results indicate that the PGPRs has improved coriander growth under control as well as salt stress conditions. Thus, PGPR can could significantly contribute to solve the coriander plant production problems caused by high salinity.

Nowadays, microorganisms that display plant growth promoting properties are significantly interesting for their potential role in reducing the use of chemical fertilizers. This research study proposed the isolation of the actinobacteria associated with arbuscular mycorrhizal fungi (AMF) spores and the investigation of their plant growth promoting properties in the in vitro assay. Three actinobacterial strains were obtained and identified to the genus Streptomyces (GETU-1 and GIG-1) and Amycolatopsis (GLM-2). The results indicated that all actinobacterial strains produced indole-3-acetic acid (IAA) and were positive in terms of siderophore, endoglucanase, and ammonia productions. In the in vitro assay, all strains were grown in the presence of water activity within a range of 0.897 to 0.998, pH values within a range of 5–11, and in the presence of 2.5% NaCl for the investigation of drought, pH, and salt tolerances, respectively. Additionally, all strains were able to tolerate commercial insecticides (propargite and methomyl) and fungicides (captan) at the recommended dosages for field applications. Only, Amycolatopsis sp. GLM-2 showed tolerance to benomyl at the recommended dose. All the obtained actinobacteria were characterized as plant growth promoting strains by improving the growth of chili plants (Capsicum flutescens L.). Moreover, the co-inoculation treatment of the obtained actinobacteria and AMF (Claroideoglomus etunicatum) spores could significantly increase plant growth, contribute to the chlorophyll index, and enhance fruit production in chili plants. Additionally, the highest value of AMF spore production and the greatest percentage of root colonization were observed in the treatment that had been co-inoculated with Streptomyces sp. GETU-1.

In smallholder farms of Côte d’Ivoire, particularly in the northeast of the country, Cajanus cajan (pigeonpea) has become an important crop because of its multiple beneficial facets. Pigeonpea seeds provide food to make ends meet, are sold on local markets and aerial parts serve as forage for animals. Since it fixes atmospheric nitrogen in symbiosis with soil bacteria collectively known as rhizobia, C. cajan also improves soil fertility and reduces fallow time. Yet, seed yields remain low mostly because farmers cannot afford chemical fertilizers. To identify local rhizobial strains susceptible to be used as bio-inoculants to foster pigeonpea growth, root nodules were collected in six fields of three geographically distant regions of Côte d’Ivoire. Nodule bacteria were isolated and characterised using various molecular techniques including matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) and DNA sequencing. These molecular analyses showed that 63 out of 85 nodule isolates belonged to two major clades of bradyrhizobia, one of which is known as the Bradyrhizobium elkanii super clade. Phylogenies of housekeeping (16S-ITS-23S, rpoB) and symbiotic (nifH) genes were not always congruent suggesting that lateral transfer of nitrogen fixation genes also contributed to define the genome of these bradyrhizobial isolates. Interestingly, no field-, plant- or cultivar-specific effect was found to shape the profiles of symbiotic strains. In addition, nodule isolates CI-1B, CI-36E and CI-41A that belong to distinct species, showed similar symbiotic efficiencies suggesting that any of these strains might serve as a proficient inoculant for C. cajan.