Rhizobial Isolates Research Articles

Efficiency Testing of Some Local Bacterial Isolates on Biodegradation for Gas Oil in Contaminated Soil Extract

A factorial experiment was carried out in glass containers using a randomized complete design (RCD) in clay soil mixture to study the test of pollination ability with four types of Rhizobium isolates isolated from the root nodes of four plants of the leguminous family. (Vigna anguiculata L (R1), Vicia faba (R2), Phaseolus (R3), Vigna radiate (R4) and a mixture of (B. megaterium, B.pumilus, B.lichenitormis, B.amylolilguefaciens) (B) on the consumption of gas oil at three levels (0, 2, 4%) by measuring the amount of CO2 released, the percentage and quantity of gas oil consumption and the concentration of the bio-emulsion produced by these isolates in industrial agricultural media. The results showed that all types of bacterial isolates led to a significant increase in the amount of CO2 released for the two levels (2%, 4%) compared to the level (0%), the treatment of adding Rhizobia bacteria isolated from the mung bean plant was recorded (R4) Vigna radiate and at the level (4%) the highest liberated amount, it reached to (390.40) mg of 100 gm-1 of soil compared to the comparison and at the level (0%) that was (126.15)) mg of 100 gm-1 of soil, resulted in a significant decrease in the residual amount of gas oil in the soil and for all levels of gas oil, and the treatment of adding Bacillus mixture recorded the lowest residual amount, it reached to (0.45) ml 100 gm-1 soil out of (2) ml added compared to the control treatment which recorded (1.75) ml 100 gm-1 soil at the level (2%). The treatment of adding a mixture of Bacillus (B) bacteria recorded the highest degraded percentage at the 2% level, which amounted to (77.5%) compared to the control treatment which recorded (12.5%), whereas, the treatment of adding Rhizobia isolated from Vigna radiate (R4) recorded the highest degraded percentage at the 4% level, which amounted to (68.75%) compared to the control treatment (23.75%). All bacterial isolates recorded the highest concentration of the bio-emulsion at the level (0%) and the lowest concentration at the level (4%), and the Bacillus bacteria mixture (B) recorded at the level (0%) the highest concentration of the bio-emulsion was (27.75) mg L-1.

USING SALT-TOLERANT RHIZOBIA TO IMPROVE THE SOYBEAN (GLYCINE MAX) RESILIENCE TO SALINITY

Soybean (Glycine max [L.] Merr.) is an economically important oilseed crop with an annual increase in growing grain demand. Soybean is a moderately salt-tolerant crop; however, salt stress conditions can affect its growth and yield-related traits and, eventually, reduce productivity. In saline soils, one of the techniques to increase soybean productivity is to use rhizobia inoculation. Although, using industrial rhizobia-based biofertilizers is often ineffective due to their lack of adaptability to salinity. Injecting soybeans with salt-tolerant and growth-promoting rhizobia helps mitigate the effects of salt stress harmful to crop plants. The recent study sought to isolate local strains of salt-tolerant rhizobia, studying its ability to increase soybean tolerance to salt stress conditions. Twenty-four local salttolerant rhizobium isolates underwent isolation from root nodules of soybean grown on saline soils. Studying their basic morphological and biochemical characteristics and ability to withstand salt stress led to the final selection of five salt-tolerant strains. The rhizobium strains were able to synthesize metabolites that stimulate growth and help reduce salt stress in plants. The study of rhizobia nodulation ability under saline conditions resulted in selecting the three most efficient strains from the Bradyrhizobium japonicum species. Inoculation of soybean seeds with salt-tolerant rhizobia proved to mitigate the adverse effects of salinity on plant growth by increasing the root size and the number of nodules in the roots. Thus, the study establishes that inoculation of soybean seeds with local salttolerant rhizobia enhances soybean tolerance to salt stress and improves crop growth and adaptation to soil salinity. Using isolated local strains of salt-tolerant rhizobia will help provide a key and environmentally friendly approach to solving the problem of salt stress for sustainable agriculture.

Isolation and Characterization of Thermotolerant Mungbean (Vigna Radiata L.) Rhizobial Isolate As Biofertilizer

Rhizobia act as primary nitrogen fixing microorganisms in the root of leguminous plants. Efficient rhizobia are helpful in increasing productivity of legumes. In the present investigation a total of twenty rhizobial isolates were retrieved from root nodules of mungbean plants growing in field during summer season. On evaluation of plant growth promoting traits of all rhizobial isolates it was found that rhizobial isolate HSR1 had maximum indole acetic acid (IAA) production (58.83 μg/ml), ammonia excretion (4.78 μg/ml) and phosphate solubilization potential. Other plant growth promoting traits like aminocyclopropane- 1-carboxylic acid (ACC) deaminase activity, siderophore production and hydrogen cyanide (HCN) production were also exhibited by isolate HSR1. This isolate was able to survive 45ºC and exhibited plant growth promoting traits at high temperature. Genomic DNA extracted from isolate HSR1 was subjected to amplification of 16S rRNA gene for identification. The similarity searching of the sequence obtained after 16S rRNA gene sequencing showed 99% similarity with Sinorhizobium sp. T25, which was confirmed by morphological and biochemical tests. Presence of good plant growth promoting traits makes HSR1 a promising strain to be developed as biofertilizer to improve soil fertility and plant growth. Bangladesh J. Bot. 52(2): 217-224, 2023 (June)

Study on diversity, nitrogen-fixing capacity, and heavy metal tolerance of culturable Pongamia pinnata rhizobia in the vanadium-titanium magnetite tailings.

The diversity, nitrogen-fixing capacity and heavy metal tolerance of culturable rhizobia in symbiotic relationship with Pongamia pinnata surviving in vanadium (V) - titanium (Ti) magnetite (VTM) tailings is still unknown, and the rhizobia isolates from the extreme barren VTM tailings contaminated with a variety of metals would provide available rhizobia resources for bioremediation. P. pinnata plants were cultivated in pots containing the VTM tailings until root nodules formed, and then culturable rhizobia were isolated from root nodules. The diversity, nitrogen-fixing capacity and heavy metal tolerance of rhizobia were performed. Among 57 rhizobia isolated from these nodules, only twenty strains showed different levels of tolerance to copper (Cu), nickel (Ni), manganese (Mn) and zinc (Zn), especially strains PP1 and PP76 showing high tolerance against these four heavy metals. Based on the phylogenetic analysis of 16S rRNA and four house-keeping genes (atpD, recA, rpoB, glnII), twelve isolates were identified as Bradyrhizobium pachyrhizi, four as Ochrobactrum anthropic, three as Rhizobium selenitireducens and one as Rhizobium pisi. Some rhizobia isolates showed a high nitrogen-fixing capacity and promoted P. pinnata growth by increasing nitrogen content by 10%-145% in aboveground plant part and 13%-79% in the root. R. pachyrhizi PP1 showed the strongest capacity of nitrogen fixation, plant growth promotion and resistance to heavy metals, which provided effective rhizobia strains for bioremediation of VTM tailings or other contaminated soils. This study demonstrated that there are at least three genera of culturable rhizobia in symbiosis with P. pinnata in VTM tailings. Abundant culturable rhizobia with the capacity of nitrogen fixation, plant growth promotion and resistance to heavy metals survived in VTM tailings, indicating more valuable functional microbes could be isolated from extreme soil environments such as VTM tailings.

Characterization, Screening and Application of Rhizobial Isolates on Black Gram [Vigna mungo (L.) Hepper] Productivity from the Rhizosphere Soil of Dibru-Saikhowa Biosphere Reserve (DSBR) Forest of Assam, India

An experiment was conducted with efficient Rhizobial isolates from the rhizosphere soil of Dibru-Saikhowa Biosphere Reserve (DSBR) forest of Assam, India in both laboratory and field condition with black gram. The purification, authentication, characterization and screening of efficient isolates viz. MDB1 (Microbial Diversity Bacteria), MDB9, MDB11, MDB12 and MDB15 have been done in vitro experiment in Gibson’s tube and Leonard jars. Lone inoculation of these five isolates in black gram with prominent parameters like dry weight (g, plant-1) of shoot and root, chlorophyll content (mg, g-1fresh wt.), N & P content (g/plant) and yield (kg, ha-1) were recorded in field condition. Dry weight of nodule (51 g, plant-1), shoot (7.80 g, plant-1) and root (3.55 g, plant-1) was observed high in MDB11 inoculation while low (nodule= 34, shoot= 5.60 and root= 2.30 g, plant-1) in MDB15. The N & P content showed high (3.15 & 1.86 mg/plant in shoot and 1.69 & 1.06 mg/plant in root) in MDB11 inoculation comparison to others. Subsequently, the highest productivity (460.48 kg, ha-1) of the test crop observed in due application of MDB11 while lowest (365.32 kg, ha-1) in MDB15. In this piece of research work, we used all the above-mentioned Rhizobium isolates as PGPR (Plant Growth Promoting Rhizobacteria) which were isolated from Dibru-Saikhowa Biosphere Reserve Forest of Assam. This study thus underlines the potentials of the rhizobial isolates correspondence to the growth and development of black gram and submits this piece of work in original form for greater benefit of mankind in future.

Effectiveness of indigenous Rhizobium sp. isolates from peatland soils on soybean (Glycine max L. Merril) growth and production

The low productivity of soybeans can be overcome by cultivating them on peatlands, accompanied by the provision of indigenous Rhizobium strains derived from peatlands. Isolating Rhizobium sp. from peatlands is believed to enhance soybean productivity on such land. This study aims to determine the effectiveness of local Riau Rhizobium sp. isolates for soybean cultivation in Riau peatlands. Six isolates of Rhizobium sp. were used in this study, obtained from plants growing on peatlands: IIMB4, IIRM1, IIRM2 from the rhizosphere of Mucuna bracteata, and IIRA4, IIRA2, IIRA6 from the rhizosphere of Acacia crassicarpa. The experiment followed a completely randomized design (CRD), with each treatment replicated four times. The treatments included control, commercial Rhizobium sp., isolates IIMB4, IIRA2, IIRA6, IIRM2, IIRA4, and IIRM1. The results demonstrated that all indigenous Rhizobium sp. isolates from peatlands, particularly IIMB4, effectively formed symbiotic associations with soybean plant roots, improving growth parameters and increasing soybean production. Nevertheless, it is also necessary to assess the effectiveness of these Rhizobium sp. isolates on various other leguminous plant species to identify the most efficient symbiotic isolates across different leguminous crops.

Molecular Characterization of Indigenous Rhizobia from Kenyan Soils Nodulating with Common Beans.

Kenya is the seventh most prominent producer of common beans globally and the second leading producer in East Africa. However, the annual national productivity is low due to insufficient quantities of vital nutrients and nitrogen in the soils. Rhizobia are symbiotic bacteria that fix nitrogen through their interaction with leguminous plants. Nevertheless, inoculating beans with commercial rhizobia inoculants results in sparse nodulation and low nitrogen supply to the host plants because these strains are poorly adapted to the local soils. Several studies describe native rhizobia with much better symbiotic capabilities than commercial strains, but only a few have conducted field studies. This study aimed to test the competence of new rhizobia strains that we isolated from Western Kenya soils and for which the symbiotic efficiency was successfully determined in greenhouse experiments. Furthermore, we present and analyze the whole-genome sequence for a promising candidate for agricultural application, which has high nitrogen fixation features and promotes common bean yields in field studies. Plants inoculated with the rhizobial isolate S3 or with a consortium of local isolates (COMB), including S3, produced a significantly higher number of seeds and seed dry weight when compared to uninoculated control plants at two study sites. The performance of plants inoculated with commercial isolate CIAT899 was not significantly different from uninoculated plants (p > 0.05), indicating tight competition from native rhizobia for nodule occupancy. Pangenome analysis and the overall genome-related indices showed that S3 is a member of R. phaseoli. However, synteny analysis revealed significant differences in the gene order, orientation, and copy numbers between S3 and the reference R. phaseoli. Isolate S3 is phylogenomically similar to R. phaseoli. However, it has undergone significant genome rearrangements (global mutagenesis) to adapt to harsh conditions in Kenyan soils. Its high nitrogen fixation ability shows optimal adaptation to Kenyan soils, and the strain can potentially replace nitrogenous fertilizer application. We recommend that extensive fieldwork in other parts of the country over a period of five years be performed on S3 to check on how the yield changes with varying whether conditions.

Polyphasic characterization of rhizobial isolates obtained from different common bean-producing regions

In Brazil, the common bean is a crop with significant social and economic importance. The prospecting of N2 fixing bacteria is crucial since biological nitrogen fixation (BNF) is an eco-friendly technique. This work aimed to obtain and characterize rhizobium isolates based on morpho-physiological, molecular, and symbiotic efficiency parameters, using the strains SEMIA 4077, SEMIA 4080, and SEMIA 4088 as references. The characteristics of the isolates and colonies, their tolerance to salinity and temperature, as well as their utilization of carbon sources, served as the basis for the morpho-physiological characterization. BOX-PCR, REP-PCR, and ERIC-PCR markers were used for genotypic characterization. Assessment of the symbiotic efficiency was carried out in a greenhouse, determining the number of nodules (NN), nodule dry weight (NDW), shoot dry weight (SDW), and total-N (Total-N) accumulation in the shoot. Among the isolates, those exhibiting: neutral culture medium pH, fast growth, colony diameter <2 mm, opaque transparency, homogeneous appearance, and cream color were predominant. Compared to temperature, salinity was the most restrictive factor to the growth of the isolates. Most of the isolates grew on sucrose (88.43%) and mannitol (87.28%). Genotypic analysis revealed that 90% of the isolates clustered in the same group as the reference strain SEMIA 4080. The TaMsG2R1 and BaDeG4R2 isolates showed higher Total-N in the shoot than the reference strains and should be evaluated in future studies under field conditions.

PHENOTYPIC AND GENETIC DIVERSITY OF NATIVE RHIZOBIUM ISOLATED FROM ROOT NODULES OF LEGUMINOUS PLANTS GROWN IN RECLAIMED SOIL, EGYPT

An investigation of the phenotypic characteristics of 19 rhizobial strains, isolated from root nodules of different plant legumes grown in the soil of agriculture farms in Ismailia governorate, transpired. Most isolates were creamy or white opaque, mucoid, with a convex elevation, translucent, and smooth margined. Microscopic investigation revealed that all bacterial isolates were rod-shaped and had no positive affinity for Gram-stain. Identifying rhizobial cultures from any bacterial contaminants employed confirmatory tests based on prepared special media, including YMA supplement with Congo red, glucose peptone agar, Kit-lactose agar, and Hoffer’s alkaline test. Based on an infectivity test, all isolates proved their ability to reinfect their host. These rhizobial isolates, classified into two categories, included fast and slow-growing rhizobia according to their growth in the YEM medium containing bromothymol blue (BTB). Meanwhile, the assessment of the genetic diversity among these isolates proceeded using ISSR and RAPD markers, which ISSR marker proved a more powerful tool in discriminating among the tested isolates than the RAPD marker. The cluster analysis, with the RAPD marker, classified the isolates into two main groups. The first group included the isolates (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 13), while the second group contained the isolates (12, 14, 15, 16, 17, 18, and 19). Moreover, using ISSR markers also showed a cluster of two main groups with diverse categories; the first cluster included isolates 1 to 11, and the second group contained isolates 12 to 19.

Biosorption and Symbiotic Potential of Horse Gram Rhizobia in Soils Contaminated with Cobalt

The current study aims evaluation of biosorption and symbiotic potential of horse gram plants associated with rhizobia inspite of Cobalt (Co) metal stress, and these rhizobia strains play a pivotal role in the phytoremediation of Co heavy metal-contaminated soils. Horse gram rhizobial isolates HGR-4, HGR-6, HGR-13 and HGR-25 were able to tolerate 1000µgg-1 Co supplemented in culture media and also 100µgg-1 in Co supplemented soil. The plants nodulated with the isolates from the study have shown higher nodulation, nitrogen and leghaemoglobin content in the potted experiment on par with the control plants. Atomic absorption spectroscopic analysis of Co content in horse gram plants inoculated with these four isolates showed maximum biosorption of Co among the bacterial root nodules. Application of these strains can be potentially aid the phytoextraction of Co from contaminated soils on association with horse gram plants.

Isolation of Rhizobia From the Nodules of Bambara Groundnuts for Inoculant Production

Rhizobia symbiotic interactions with legumes fix atmospheric nitrogen into the soil, which is essential in amending the characteristically low-nitrogen soils in most farming communities in northern Ghana. A high potential for improvement of Bambara groundnuts production in low-nitrogen soils is by the exploitation of colonization of the plant roots with rhizobial inoculation. This experiment sought to isolate Legume Nodulating Bacteria (LNB) obtained from root nodules of Bambara groundnut (Vigna subterranea) plants and to identify effective strains for improved production of the crop. Roots nodules of Bambara plants used in this study were obtained from preserved plants and the isolates were authenticated for their symbiotic effectiveness under screen house conditions. Nodulation of the isolates was examined in plastic pots containing sterile river sand and test crop (Bambara seeds). The experiment included reference strains, a positive nitrogen control and an un-inoculated control. The results were obtained after two months of data collection. The difference in results was explained via nodulation capacity. Out of the two isolates obtained, 2CL showed a high nodulation capability, rating it as highly effective. The outcome of this study provides stakeholders with the prospect for the use of effective isolates as inoculants to improve Bambara groundnut yield in general and in northern Ghana in particular.

Effects of Indigenous and Commercial Rhizobia on Growth and Nodulation of Soybean (Glycine max L) under Greenhouse Condition

Background: Soybean (Glycine max L.) is the most vital grain legume crop rich in protein and oil. The inoculation of rhizobia with soybean plays a very important role in increasing soil fertility via its contribution to biological nitrogen fixation. Objective: This study focuses on the evaluation of indigenous and commercial rhizobia on soybean nodulation and growth parameters. Methodology: Soil samples were collected from five districts for nodule trapping. The rhizobia were isolated using ‘plant induction following the standard procedures. The greenhouse experiments were arranged in a completed randomized design with three replications and two control units. The data were collected for plant height, nodule number, nodule dry weight, shoot dry weight, root length; root dry weight, total nitrogen and nitrogen-content. Results: The entire isolates were found gram-negative, without absorbing congo-red and did not grow on peptone glucose agar media. Slow grower isolates turned bromothymol blue with yeast extract mannitol agar medium into a moderately deep blue color but fast grower changed to yellow color. All isolates were tested on the sand induced nodule and were significantly superior to the negative control in terms of plant height, shoot dry weight, and nodule dry weight. The shoot dry weight of soybean rhizobial isolates on the sterilized sand experiment was ranging from 1.6 to 2.2g per plant and it was a highly significant correlation to the nodule number, nodule dry weight and root dry weight. Conclusion: The indigenous isolates were highly competent to all commercial rhizobia. This study encourages further evaluation of the field and molecular characteristics.

CHARACTERIZATION OF RHIZOBIUM ISOLATES AS BIOCONTROL AGENTS AGAINST FUSARIUM SOLANI AND MACROPHOMINA PHASEOLINA

This study recovered 15 Rhizobium and Bradyrhizobium isolates from nodules of different legume plants (Faba bean, Pea, Soybean, and Clover) grown in nine Egyptian governorates representing the delta region (Menoufia, Gharbia, Suez, Qalubia, Cairo, Sharkia, Behirah, Kafr El-sheikh, and Ismailia). The infectivity test proceeded with all isolates retaining and infecting their hosts, demonstrating that they are Rhizobium cultures. Molecular identification based on 16S rRNA gene sequencing revealed that the isolates belonged to two species of Rhizobium, namely Rhizobium leguminosarum (RL1, RL2, RL3, RL4, RL5, RL6, RL7, RL8, RL9, RL10, RL11, RL12, and RL13) and Bradyrhizobium japonicum (BJ1 and BJ2). Moreover, PCR based on specific primers was employed to detect nifH gene in the genomes of tested isolates. Most of the isolates exhibited sensitivity toward antibiotics, and were able to produce HCN. The isolates of RL4, RL6, RL9, and RL10 were positive for chitinase activity and exhibited clear zones ranging from weak to sturdy. The antagonism evaluation of Rhizobium isolates against Fusarium solani and Macrophomina phaseolina ensued under in vitro conditions. The isolates RL6 and RL9 of R. leguminosarum were the most effective, suppressing more than 50% growth of M. phaseolina. Similarly, the isolates RL4, RL6, RL9, and RL10 revealed the most effective and inhibited more than 50% growth of F. solani. Interestingly, the isolates RL6 and RL9, which exhibited high levels of suppression against M. phaseolina, also displayed high levels of suppression against F. solani.

Collection, Isolation and Symbiotic Efficiency Test and Field Evaluation of Native Rhizobia for Soybean (<i>G. max</i>) in Acid-Prone Areas of South-West Ethiopia

Because of the rising costs of chemical fertilizers and the growing environmental concerns, there is a need in the use of bio-inoculants in crop production and soil fertility enhancement. A field study was therefore conducted at Jimma zone Kersa and Nadi gibe District during 2019/2020 and 2020/2021 main cropping season to evaluate soybean nodulating rhizobia isolates under field condition in order to select the best performing rhizobia strain for nodulation, yield and yield attributes of soybean. Eight treatments were arranged in RCBD with three replications. Nodule number, number of pods per plant, dry biomass and grain yield was responded significantly to the interaction effects of Tgp-3 inoculation. The maximum mean yield of 2506.5kg per hectare and mean dry biomass of 8.12 ton per hectare was obtained from Tgp-3 inoculation. Similarly the highest mean nodule number of 298.68 per plant was counted after inoculation with Tgp-3. Similarly the highest mean number of pods per plant was obtained by inoculation of Tgp-3. These results demonstrated that the dominance of Tgp-3 rhizobium isolate and could explain the effectiveness of the isolate in South west soil of Ethiopia. Inoculation of Tgp-3 isolate with Clark 63-K soybean variety was being considered effective symbionts for Clark 63-K soybean production in the area.

Isolation and Characterization of Rhizobium from Green Gram (Vigna radiata)

Nitrogen is a crucial component that acts as building blocks for nucleic acids and proteins. It is abundantly present in atmosphere of the earth but plants are not able to easily utilize it. Diazotrophic microorganisms such as Rhizobium convert N2 and make it available to pulse crops. In the present study, a total of thirty-four Rhizobium isolates were recovered, from that twenty-two with gram-negative-rods were biochemically characterized. Most of the isolates were negative for congo red (CR) absorption, glucose-peptone, lactose, and hofer’s alkaline assays. These isolates have PGP (plant growth promoting) properties such as solubilisation of mineral, growth hormone, and hydrogen cyanide (HCN) productions along with antagonistic activity. Plant study revealed that SBGR25 treatment has highest germination per cent (98.0 %), shoot (10.3 cm) and total-height (16.6 cm), and dry weight (5.60 g). Hence, the present study suggests that SBGR25 strains could be used as promising bioinoculants for the pulse crop.

​Plant Growth Promoting Mesorhizobia as a Potential Inoculant for Chickpea (Cicer arietinum L.): A Review

Chickpea establish symbiotic relationship with Mesorhizobium ciceri and fixes atmospheric nitrogen, which depends on the efficacy of the Mesorhizobium strains, crop management, soil and environmental factors. A multi-trait Mesorhizobium isolate having more than one Plant growth promoting (PGP) traits often stimulates plant growth directly by IAA and GA production, enhances nutrient uptake by solubilizing phosphorus and siderophore production while indirect growth promotion is by prevention of some pathogenic microorganisms by producing HCN. Several studies revealed that plant growth attributes and yield was increased with inoculation of multi trait Rhizobium isolates. The occurrence of different PGP traits of Mesorhizobium and their effects on plant growth will be discussed in this review paper.

Treatment with atypical rhizobia, Pararhizobium giardinii and Ochrobactrum sp. modulate the rhizospheric bacterial community, and enhances Lens culinaris growth in fallow-soil

Diazotrophic nodule isolates are acknowledged promoters of plant growth and rhizospheric community. Consequently, in the lentil agroecosystem, inoculation of atypical rhizobial isolates could be a viable alternative to chemical fertilizers for fallow land usage optimization. The aim of this study is to evaluate and select the rhizobial isolates of lentil nodules with plant-growth-promoting (PGP) attributes and to elucidate their application in rice-fallow soil for determining the growth of lentils and its impact on the rhizospheric bacterial community. Lentil’s nodule isolates were identified and screened for their PGP attributes, biofilm, exopolysaccharide (EPS) formation, and early plant growth promotion. The pot experiment with the selected atypical rhizobial isolates Pararhizobium giardinii (P1) and Ochrobactrum sp. (42S) significantly enhanced germination, vigour index, nodule formation (P1 60%, 42S 42% increase), nodule fresh weight, shoot length (65% P1 & 35% 42S), and chlorophyll content as compared to the uninoculated control treatment. The genes for nitrogen fixation nifH and nifK were detected in both isolates. Scanning Electron Microscopy (SEM) revealed successful root and nodule colonization by both isolates, while Transmission Electron Microscopy (TEM) displayed nitrogen-fixing zones within root nodules. Proteobacteria predominated in the lentil rhizosphere of all the treatments. Whereas, application of either P1 or 42S increased Rhizobium, Mesorhizobium, and Bradyrhizobium genra, thus positively modulating rhizospheric community structure. The correlation network analysis revealed an abundance of some interdependent bacterial genera with a possible role in overall plant growth. Functional genes for siderophore biosynthesis and ABC transporter were positively modulated by application of either P1 or 42S. This study showed the significant effect of P. giardinii P1 and Ochrobactrum sp. 42S of L. culinaris on lentil growth, improving fallowsoil health for optimum usage, and modulated rhizospheric community structure which strongly manifest prospects of low-cost, eco-friendly and sustainable biofertilizers.

Plant Growth Promoting and Abiotic Stress Tolerant Chickpea (Cicer arietinum L.) Rhizobial Isolates from Some Areas of South Wollo Zone, Ethiopia

Chickpea (Cicer arietinum L) is an important pulse crop prized for its high protein content and is grown as a food source worldwide, including Ethiopia. However, the yield of chickpea is low due to low soil fertility and the ever-changing abiotic stresses. Therefore, this study aimed at isolation, characterization, and selection of chickpea rhizobia effective in their nitrogen fixation and abiotic stress tolerance potential. As a result, 150 nodule samples were collected from three districts of chickpea-producing areas in South Wollo. The nodules were crushed, and the rhizobia were isolated and characterized by using standard microbiological procedures. Based on the presumptive tests conducted, 103 (68.7%) of the rhizobial isolates were tentatively categorized as Rhizobium species. Regarding phosphate solubilization, only 48 (46.7%) solubilized phosphate with a solubilization index ranging from 2.1 to 2.7 mm. Twenty-four (50%) of the isolates were found to be hydrogen cyanide producers. Among the rhizobial isolates tested under greenhouse conditions, 37 (77.1%) of them induced nodulation on their host plant (chickpea). Their symbiotic effectiveness evaluation test confirmed that 16(47.1%), 6(17.6%), 26.47%, and 3(8.8%) were highly effective, effective, low effective, and ineffective, respectively. Of the authenticated rhizobial isolates, 12 (35.5%) of them, including WuCR-15, 16, 17, 18, 19, 20, 23, 30, 31, 32, 36, 38, and 48, accumulated higher shoot dry matter than the positive control. Isolates WuCR- 11, 17, and 36 showed resistance to low and high extreme abiotic stresses of pH, temperature, and salt. Consequently, rhizobial isolates, WuCR- 11, 17, and 36, which were effective and competent in all the tested parameters, were recommended as good rhizobial candidates for applications under greenhouse and field conditions.

Genetic diversity of rhizobia isolated from nodules of Trigonella foenum-graecum L. (fenugreek) cultivated in Northwestern Morocco

The present work aimed to characterize rhizobia nodulating Trigonella foenum-graecum L. (fenugreek) cultivated in six different geographical locations in Northwestern Morocco. Forty-seven rhizobial isolates from nodules of Trigonella foenum-graecum were grouped into thirteen clusters using the Rep-PCR technique. The phylogenetic analysis based on 16S rRNA gene sequences of 13 groups showed that all representative strains were closely related to members of the genus Ensifer (syn. Sinorhizobium) of the Alphaproteobacteria. All the representative strains shared 100% similarity with Ensifer medicae WSM419T. NodC and nifH gene analysis revealed a close phylogenetic relationship of the representative strains with those of the strains belonging to the symbiovar meliloti. Furthermore, nodulation ability of our rhizobial strains was efficient in their host plant (Trigonella foenum-graecum L.).

Sole carbon source utilization (SCSU) pattern of nodule forming rhizobia of Sesbania species

Nitrogen fixing rhizobia promises another method to plant N fertilizer supplies. Growing high N2-fixingplants like Sesbania is useful not only for economic perspective but also for soil amelioration. Along withthe phenotypic criteria, carbon utilization is more perceptive than other methods like intrinsic antibioticresistance. Selected rhizobial isolates of various Sesbania spp. were used to evaluate the sole carbon sourceutilization (SCSU) pattern by means of twenty two diverse sugars. The analysis of the data using NTSYSPCsoftware resulted in diversification of the rhizobial isolates into two major groups and divergenceamong them started at 48% level of similarity coefficient. Dextrose was the isolates’ most commonly usedcarbon source (88%), whereas inulin was the least.