Rhizobacterial Isolates Research Articles

Rhizobacterial Colonization and Management of Bacterial Speck Pathogen in Tomato by Pseudomonas spp.

Plants and soil microorganisms interact at every stage of growth. Pseudomonas spp. are highly regarded for their ability to increase crop production and protection from diseases. The aim of this study is to understand the mechanisms of the rhizobacterial colonization of tomato roots via chemotaxis assay and the activation of tomato resistance against the pathogenic bacterium, Pseudomonas syringae pv. tomato DC3000 (Pst). The capillary assay was used to evaluate the chemotaxis response of PGPRs (plant growth-promoting rhizobacteria). The activities of defense enzymes and the expressions of PR (pathogenesis-related) genes were measured using real-time qPCR. Chemotactic responses to malic and citric acids (the most important root exudates found in different plant species) at low concentrations varied substantially among the rhizobacterial isolates (63 species). Beneficial isolates including Pseudomonas resinovorans A5, P. vranovensis A30, P. resinovorans A28, P. umsongensis O26, P. stutzeri N42, and P. putida T15 reacted well to different concentrations of root exudates. P. putida T15 demonstrated the most potent anti-Pst activity. At three and six days after inoculation, the greatest levels of polyphenol oxidase and peroxidase activity were reported in the A5 and T15 groups. In tomato, transcript levels of four PR (pathogenesis-related) genes were elevated by rhizobacterial treatments. PGPR isolates alone or in combination with BABA (β-amino butyric acid) up-regulated the transcriptions of PR1, PR2, LOX, and PAL genes. Treatments with N42 and T15 resulted in the greatest improvements in tomato growth and yield traits. In conclusion, the results explain the mechanisms of rhizobacterial colonization for the improved management of Pst. Rhizobacterial isolates play a role in tomato’s resistance to Pst via salicylic acid and jasmonic acid pathways.

Rhizobacteria Bacillus spp. enhance growth, influence root architecture, physiological attributes and canopy temperature of mustard under thermal stress

In arid and semi-arid regions, high temperature stress is one of the most common abiotic stresses affecting plant growth and development, as well as agricultural output. Growth and establishment of mustard, an important oilseed crop, is affected due to increased incidences of higher-than-normal temperatures during sowing of the crop. In the present study, we screened rhizobacterial isolates for their thermotolerance. Under high temperature stress, three thermotolerant rhizobacterial cultures were assessed for their plant growth promoting activities. There was beneficial effect of high temperature on their indole acetic acid and gibberellic acid production abilities. A pot experiment was conducted to evaluate the effect of the three rhizobacterial strains on mustard growth under high temperature stress. Inoculation with the rhizobacteria significantly improved plant biomass, root architecture and physiological attributes – relative water content, membrane stability index and chlorophyll content. There were lowering of hydrogen peroxide content and lipid peroxidation. Increased total leaf area and lowering of canopy temperature was observed in the inoculated plants, under high temperature. Significant positive correlation was observed between plant biometric traits and most of the physiological attributes, while negative correlation was observed with lipid peroxidation and hydrogen peroxide content. Under both no stress and high temperature stress, response to inoculation with Bacillus sp. strain MRD-17 was markedly more than the other rhizobacterial strains. Thus, these rhizobacteria were able to enhance thermotolerance of mustard during early stages of growth. As a result, thermotolerant rhizobacteria with plant growth-promoting activity can be utilized to alleviate high temperature stress in crops.

Bacillus amyloliquefaciens PKM16 acts as an antagonist of white mold and an inducer of defense enzymes in tomato plants

This study aimed to investigate the potential of rhizobacteria isolated from tomato plants to control Sclerotinia sclerotiorum and induce the activity of pathogenesis-related enzymes in Micro-Tom tomato plants. Three rhizobacterial isolates were evaluated to determine the most efficient antagonist agent, which was later identified by gene sequencing as Bacillus amyloliquefaciens PKM16. The antagonistic effects of B. amyloliquefaciens against S. sclerotiorum were assessed in vivo and in vitro using live and autoclaved cultures at concentrations of 0% (control), 20%, 30%, and 40% (v/v). The residual effects of four treatments (20% live culture, 20% autoclaved culture, a Bacillus subtilis-based commercial product, and autoclaved distilled water) on tomato plants inoculated with S. sclerotiorum were determined. The same treatments were also used to assess the myceliogenic germination of sclerotia and induction of plant defense enzymes (peroxidase, catalase, polyphenol oxidase, phenylalanine ammonia-lyase, and β-1,3-glucanase) in tomato plants. The live culture had a residual effect for 4 days and inhibited sclerotial germination by approximately 30%. Furthermore, live and autoclaved bacterial growth cultures stimulated enzyme activity. Therefore, B. amyloliquefaciens PKM16 was antagonistic to S. sclerotiorum, effectively inhibiting mycelial growth and activating defense mechanisms in Micro-Tom tomato plants.

Potential of desiccation-tolerant plant growth-promoting rhizobacteria in growth augmentation of wheat (Triticum aestivum L.) under drought stress.

Wheat (Triticum aestivum L.) yield and physiology are adversely affected due to limited water availability. However, desiccation-tolerant plant growth-promoting rhizobacteria (DT-PGPR) are potential candidates that can overcome the negative impacts of water stress. In the present study, a total of 164 rhizobacterial isolates were screened for desiccation tolerance up to -0.73 MPa osmotic pressure, of which five isolates exhibited growth and expression of plant growth properties under the influence of desiccation stress of -0.73 MPa. These five isolates were identified as Enterobacter cloacae BHUAS1, Bacillus cereus BHUAS2, Bacillus megaterium BHUIESDAS3, Bacillus megaterium BHUIESDAS4, and Bacillus megaterium BHUIESDAS5. All five isolates exhibited plant growth-promoting properties and production of exopolysaccharide (EPS) under the impact of desiccation stress. Furthermore, a pot experiment on wheat (variety HUW-234) inoculated with the isolates Enterobacter cloacae BHUAS1, Bacillus cereus BHUAS2, and Bacillus megaterium BHUIESDAS3 exhibited a positive influence on the growth of wheat under the condition of water stress. A significant improvement in plant height, root length, biomass, chlorophyll and carotenoid content, membrane stability index (MSI), leaf relative water content (RWC), total soluble sugar, total phenol, proline, and total soluble protein, were recorded under limited water-induced drought stress in treated plants as compared with non-treated plants. Moreover, plants treated with Enterobacter cloacae BHUAS1, Bacillus cereus BHUAS2, and Bacillus megaterium BHUIESDAS3 depicted improvement in enzymatic activities of several antioxidant enzymes such as guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Beside this significant decrease in electrolyte leakage, H2O2 and malondialdehyde (MDA) contents were also recorded in treated plants. From the results obtained, it is evident that E. cloacae BHUAS1, B. megaterium BHUIESDAS3, and B. cereus BHUAS2 are the potential DT-PGPR having the capability to sustain growth and yield, alleviating the deleterious effect of water stress in wheat.

Assessment of cumulative microbial respiration and their ameliorative role in sustaining maize growth under salt stress

Cumulative microbial respiration reflects microbial activities and their potential to support plant growth, where salt tolerant rhizobacteria can optimize their respiration, and ensure plant survival under salt stress. We evaluated cumulative microbial respiration of different salt tolerant rhizobacterial strains at different salinity levels, and checked their ability to sustain plant growth under natural saline conditions by using maize as test crop. Our results revealed that at the highest EC level (10 dS m−1), strain ‘SUA-14’ performed significantly better, and exhibited the greatest cumulative respiration (4.2 fold) followed by SHM-13 (3.8 fold), as compared to un-inoculated control. Moreover, results of the field trial indicated a similar trend, where significant improvements in shoot fresh weight (59%), root fresh weight (80%), shoot dry weight (56%), root dry weight (1.4 fold), leaf area (1.9 fold), straw yield (41%), cob diameter (33%), SPAD value (84%), yield (99%), relative water contents (91%), flavonoid (55%), 1000 grain weight (∼100%), soluble sugars (41%) and soluble proteins (45%) were observed due to inoculation of strain ‘SUA-14’ as compared to un-inoculated control. Similarly, substantial decline in leaf Na+ (34%), Na+/K+ ratio (69%), electrolyte leakage (8%), catalase (54%), peroxidase (73%), and H2O2 (50%) activities were observed after inoculation of ‘SUA-14’ with a concomitant increment in the leaf K+ contents (70%) under salinity stress than un-inoculated control. Hence, among all the tested rhizobacterial isolates, ‘SUA-14’ served as the most efficient strain in alleviating the detrimental impacts of salinity on maize growth and yield. The 16S rRNA sequencing identified it as Acinetobacter johnsonii.

Potential Rhizospheric Bacteria of Local Rice Rice “Cempo Laut” in Merauke

Non-cultivated local rice is known to have high resistance to various environmental stresses. This resistance is inseparable from the role of symbiotic and non-symbiotic rhizosphere bacteria that live in the root rhizosphere. This study aims to isolate and study the potential of rhizobacteria that live around the roots of non-cultivated local rice plants. This research is exploratory research to obtain rhizobacterial isolates that can stimulate plant growth and development and can be applied to cultivated rice plants. Soil samples were taken from Mimi Baru Village, Jagebob District. Sampling was carried out aseptically. Isolation was carried out using the multilevel dilution method. Isolates grown in NA media were then subcultured to obtain pure isolates. The isolates obtained were then characterized morphologically according to Bergey's Manual of Determinative Bacteriology and characterized microscopically. Based on the results of this study it can be concluded that there were 12 bacterial isolates in the local rice "Cempo Laut" which were suspected to be Bacillus and Pseudomonas. The results of this study need to be tested further to determine the effect on plant growth and development.
 

Exo-polysaccharide producing bacteria can induce maize plant growth and soil health under saline conditions

ABSTRACT Salt tolerant plant growth boosting rhizobacteria can play an important function in plant salinity stress mitigation. In the current investigation, only two rhizobacterial isolates out of 68 produced exo-polysaccharide at the fastest rate and exhibited plant growth promoting properties such as IAA, CAT, APX production, and phosphate solubilization at 6% NaCl (w/v) concentration. Both isolates had synergistic PGP features and were compatible with one another. Isolate SP-20 was identified as Kluyvera sp. and SP-203 was identified as Enterobacter sp. -by 16SrDNA sequencing. After 30, 60, and 90 days, the combination of SP-20 and SP-203 enhanced the physicochemical parameters in the maize plant in comparison to the control. By increasing soil enzymes like DHA and PPO, both isolates significantly improved the soil health matrix. When a group of these isolates were inoculated into 1% and 2% NaCl (w/v) supplemented soil, the absorption of Na in the shoot and root of maize plants was inhibited by around 50%. The BCF values for all treatments were less than TF, and the values of BCF and TF were less than one. Therefore, the present study illustrated that the novel native isolates play a remarkable role to mitigate salinity stress in maize plant.

Functional traits and phylogenetic analysis of top-soil inhabiting rhizobacteria associated with tea rhizospheres in North Bengal, India

Rhizobacteria associated with cultivated crops are known to stimulate plant growth through various indirect or direct mechanisms. In recent years, the host list of plant growth promotion/promoting rhizobacteria has expanded to include bean, barley, cotton, maize, rice, vegetables, peanut, rice, wheat, and several plantation crops. However, interaction of rhizobacteria with tea plants of organic and conventional tea gardens is poorly understood. In the present study, rhizobacterial species associated with tea rhizosphere were isolated from 14 tea gardens located in North Bengal, India. In total, 16 rhizobacterial isolates isolated from collected soil samples were assessed for antagonistic and plant growth promotion/promoting activity under laboratory conditions. Molecular characterization based on sequencing of 16S rRNA gene revealed dominance of Bacillus with five species followed by Pseudomonas with two species. Interestingly, only one isolate was affiliated with actinobacteria, i.e., Microbacterium barkeri. Out of 16 isolates, isolates Bacillus subtilis OKAKP01, B. subtilis BNLG01, B. paramycoides BOK01, M. barkeri BPATH02, and Stenotrophomonas maltophilia BSEY01 showed highest growth inhibition against Fusarium solani (68.2 to 72.8%), Pseudopestalotiopsis theae (71.1 to 85.6%), and Exobasidium vexans (67.4 to 78.3%) causing respective Fusarium dieback, gray blight, and blister blight diseases in tea crop. Further, these five isolates also possessed significantly greater antifungal (siderophore producer, protease, chitinase, and cellulase activity) and plant growth promotion/promoting (indole-3-acetic acid production, ACC deaminase, ammonia, and phosphate solubilization) traits over other eleven rhizobacterial isolates. Therefore, these five isolates of rhizobacteria were chosen for their plant growth promotion/promoting activity on tea plants in nursery conditions. Results from nursery experiments revealed that these five rhizobacteria significantly improved growth rates of tea plants compared with the control. Therefore, this study suggests that these rhizobacteria could be used to formulate biopesticides and biofertilizers, which could be applied to sustainable tea cultivation to improve crop health and reduce disease attack.

Evaluation of compatibility of native plant growth promoting rhizobacterial isolates against chemical pesticides

Conventional agriculture relies heavily on chemical fertilizers, pesticides and weedicides to control plant diseases, pests and weeds to improve production. Consequently, the soil receives the bulk of complex agrochemical compounds many of which are poisonous to the activity of non-target beneficial soil microorganisms. There is a need to check the tolerance of biocontrol agents like Plant Growth Promoting Rhizobacterial (PGPR) to various pesticides before their practical application. Taking this into account, the investigation was conducted for the screening of the PGPR isolates against chemical pesticide degradation potentialities in Plant Bacteriological Laboratory, Department of Plant Pathology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal during 2021-22. All the native rhizobacterial, Bacillus and Fluorescent pseudomonad isolates tested had good potentiality to tolerate Carbendazim and Glyphosate. Among native Bacillus isolates, BRB89, BRB42, PR 19, PR 20, BRB 52, BRB 56, BRB 74, and SM 9 showed moderate tolerance, whereas among all the native Fluorescent pseudomonads, all except GP2 showed high tolerance against Paraquat. All native Bacillus isolates except PR16 were highly sensitive against Chorpyriphos. However, all the native fluorescent pseudomonads showed tolerance against Chorpyriphos even at 2000 ppm concentration.

MINING OF 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID DEAMINASE EXHIBITING WATER STRESS TOLERANT NOVEL RHIZOBACTERIAL ISOLATES

An investigation was carried out to isolate, characterize and identify the rhizobacterial isolates of crop plants grown in the arid region of the North-eastern Karnataka.Twenty-one strains out of 120 rhizobacterial isolates that grew vigorously at-0.30Mpa were selected, and strains were biochemically characterized and screened in vitro to determine their water stress tolerance activity. Among 21 isolates, APPP-1 and GPPP-1 showed ACC deaminase activity (5.13 µMmg-1/h and 2.69µMmg-1/h, respectively). The isolate BSOP-1 produced higher proline (138.87µMmg-1) and IAA (68.49 µg ml-1); while NONB-2 produced higher exopolysaccharides (23.53mg mg-1 protein) at-0.30Mpa. Our study recorded the ACC Deaminase activity of the isolates, APPP-1and GPPP-1 later identified as a novel strain of Pseudomonas sp. VG309(NCBI accession number MH664930) and Corynebacterium kroppenstedtii (NCBI accession number MH671918) through 16SrDNA molecular sequencing technique

Isolation, and Characterization of Indigenous Rhizobacteria from Wheat (Triticum aestivum L.) and Determining their Drought Tolerance

Agricultural productivity is under serious threat as a result of the increased severity of droughts brought on by human activity and global warming. Hence, to ensure the security of the world's food supply, this has increased the demand for environmentally friendly alternatives. Numerous studies have associated the rhizobacteria that promote plant growth with the plants' adaptations to fluctuating environments. The present study was conducted over a period of 6 months, during which the drought tolerance potential of native bacteria from the Wheat (Triticum aestivum L.) rhizosphere was evaluated. A total of 10 different bacteria were isolated from the rhizosphere of flowering-stage wheat plants growing in the departmental garden of SSJ University, Almora, Uttarakhand by serial dilution technique. After a biochemical analysis, their drought tolerance potential was investigated and growth was monitored. Out of a total of ten isolates, only three were able to grow at 25% PEG. The ideal temperature range for the growth of these 3 rhizobacterial isolates was found to be 28-37℃. The present study highlights the role of rhizospheric bacteria in augmenting plant growth by providing drought tolerance.

Effect of rhizobial isolates and nitrogen fertilizer on shisham (Dalbergia sissoo Roxb.) soil properties

A treatment combination of isolates and N-based fertilizer was observed for effect on the rhizospheric soil of Dalbergia sissoo. Various blends of two plant growth-promoting rhizobacteria (PGPR1 and PGPR2) and nitrogen fertilizers (Treatments T1 to T10) have been applied to analyze their effects on the rhizospheric soil’s microbial count, physicochemical properties, and available soil NPK contents. The treatments did not produce any significant changes in the soil’s pH, electrical conductivity, or organic carbon content. However, a significant increase was observed in the nitrogen, phosphorus, and potassium contents of the rhizospheric soil, with the highest increase observed in soil treated with treatment T4, composed of the two rhizobacterial isolates utilized in this study.

Evaluation of the compatibility between native rhizobacteria isolates

Compatibility between the Plant Growth Promoting Rhizobacteria (PGPR) microbes to colonize the root system without inhibiting each other is a pre-requisite for successful benefit of using multiple microbes in a crop field. Taking this into account, the present investigation was conducted to test the compatibility between different native rhizobacterial isolates in-vitro in the Plant Bacteriological Laboratory, Department of Plant Pathology, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal during 2021- 22. All the efficient and native rhizobacterial isolates tested were compatible with each other under in-vitro conditions except BRB 88 and BRB 89, BRB 35, BRB 42, BRB 52, PR 19; BRB 89 and BRB 35, SM 9, SM 14; BRB 35 and PR 19; BRB 42 and PR 18; BRB 52 and SM 9; CK2LPP and CK2LP12, GP2, GP8, G11SP37, K11SP4, SS2LP; CK2LP12 and GP2; GP8 and K11SP4; SS2PLP and SS2PP; GP2 and G1SP37, SS2PP; G11SP37 and K11SP4; SS2PP and S21SP14; BRB 88 and CK2LPP, GP2; PR 16 and SS2PP, S21SP14; PR 20 and GP8; BRB 52 and CK2LPP, CK2LP8, GP2, GP8; BRB 56 and GP2, GP8; SM 9 and CK2LPP, CK2LP8, CK2LP12, G11SP37.

Exploration of Saurashtra Soil PGPR Strain and its Attributes in Crop Productivity by Pot Plant Study

The impact of rhizobacteria with PGPR trait in current agriculture practices is expanding its horizons at large in research and practices. The urge of improvised crop productivity and disease management for economically important myriad crops like cereal plant, and angiosperms, monocots, dicots need to address in versatile manner with integrated approach. The need of a potent trait of PGPR rhizobacteria and its real time application in field trials is more challenging and to address the same, the present research study has been carried out. The present study encompassing the one phase of the project is to isolate the Rhizobial trait from the soil sample followed by the screening of the potent traits. Total 4 potent rhizobacterial isolates have been screened among 41 bacterial isolates from different sites of the Saurashtra region. Qualitative and quantitative characterization of growth promotion factors such as HCN production, ammonia production, IAA production, and siderophore production of the isolates (KS2, KC8, KC9, and KC11 showed) were carried out. Among 21 isolates the 4 isolates KS2, KC8, KC9, and KC11showed the highest growth parameter production and have been stated as PGPR traits. Employing One way ANOVA a statistical design, the shoot and root length effect has been studied in detail with the individual strains KS2, KC8, KC9, and KC11 along with control. The study is quite encouraging with improved root length 10.54±0.33 cm and shoot length 27.20 ± 0.8 cm respectively. The future prospect of this study can be highlighted in long-term with further analysis on consortial development and its field trial applications.

ANTIFUNGAL AND ANTIBACTERIAL ACTIVITY OF RHIZOBACTERIAL MICROFLORA

Rhizospheric microorganisms like bacteria and fungi are renowned in enhancing the growth of crop plants and to inhibit other hurtful soil micro-organisms. Current research investigations were undertaken to explore such type of rhizobacteria from rice soil. Inhibitory effect of these bacteria was checked against Fusarium oxysporum f. sp. cepae and Agrobacterium tumifacians. Research outcomes unveiled that all tested rhizobacterial isolates exerted antagonistic effect against both the tested pathogens. They produced 0.8% to 1.68% inhibitory zone against fungus and 20 to 40 % against bacteria. It can be therefore, assumed that these antagonistic bacterial strains may be employed as biocontrol inoculants against fungal and bacterial diseases of agricultural crops.
 Kee words: Rhizobacteria, biocontrol, diseases, fungi and crops.

Comparison of diversity and zinc solubilizing efficiency of rhizobacteria obtained from solanaceous crops under polyhouse and open field conditions

ABSTRACT Zinc-solubilizing bacteria (Zn-SB) play a crucial role in regulating soil fertility and plant health by maintaining Zn availability in the rhizosphere. It is uncertain how the Zn-SB population fluctuates across various cultivation systems since varied land-use patterns for agricultural aims may affect microbial activity and plant development effectiveness. The current study aims to examine the Zn-SB potential of various farming systems using Solanum lycopersicum, Solanum melongena, and Capsicum annuum grown in polyhouse soil (PS) and open fields (OF). Only twenty rhizobacterial isolates from PS and two isolates from OF out of 80 showed a strong ability to solubilize Zn, which was evaluated using Atomic Absorption Spectroscopy. Bacterial strain-PS4 solubilized 253.06 ppm of ZnO and produced a high quantity of lactic acid (168.62 g/ml) and acetic acid (470.5 g/ml), whereas bacterial strain OF1 solubilized 16.02 ppm of ZnO by releasing glycolic acid (42.89 g/ml), lactic acid (22.30 g/ml), formic acid (106.03 g/ml), and acetic acid (48.5 µg/ml). Further, in vitro studies demonstrated higher production of auxin, gibberellic acid and siderophore by PS1 as compared to OF1 strain. A large diversity of Zn-SB in the soil was indicated by biochemical analysis, which revealed that isolates belonged to the families Enterobacteriaceae, Bacillaceae, Burkholderiaceae, Streptococcaceae, Paenibacillaceae, Micrococcaceae, Morganellaceae, and Dietziaceae. The isolates PS4 and OF1 were identified as Bacillus cereus and Enterobacter hormaechei, respectively, using 16S rRNA sequencing. The findings show that soil from polyhouses has a greater diversity of Zn-solubilization rhizobacteria than soil from open areas. The findings suggested a potential land-use method for enhancing crop yields by employing microorganisms and polyhouse technology, which could be useful in the future study.

Suppression of Fusarium Wilt of Chickpea by Bacillus spp., Pseudomonas sp. and Rhizobacterial Isolate

This experiment was conducted to evaluate the antagonistic effects of some selected rhizobacteria on Fusarium oxysporium f. sp. ciceris in a pot experiment. Rhizobacterial isolates (one isolate of Pseudomonas, eight isolates of Bacillus genera and one bacterium isolate) and two chickpea cultivars (Shendi and Burgeig) were arranged in a factorial pot experiment in CRD with four replicates. The disease incidence and severity were detected weekly. Disease reduction percentage was estimated at the end of the study. Generally, the application of rhizobacterial isolates as biological control agent reduced disease incidence compared with the control in both cultivars. The incidence in cultivar Shendi occurred at the third week after inoculation when treated with Pseudomonas stutzeri strain W28 (SA3) and Bacillus subtilis strain CM14(SA9). For the two cultivars, Shendi and Burgeig, the Geobacillus sp. CRRI-HN-1(SA2) and Bacillus sp (SA1), respectively had the highest positive effect on disease incidence and severity throughout the experiment compared with the control. These were 45.36 and 44.82% in incidence; 55.36 and 63.89% in severity, respectively.

Fodder radish aqueous extracts and associated rhizobacteria as bio-stimulants on tomato growth

ABSTRACT Use of bio-stimulants can reduce amounts of synthetic chemicals for improving tomato (Solanum lycopersicum L.) growth and production. The investigation evaluated the rhizobacterial isolates B45, B46, B48, B54 and B55 associated with fodder radish (Raphanus sativus L.) and its aqueous extracts for their ability to promote growth of tomato plants under greenhouse conditions. Rhizobacteria were applied by root dipping followed by seedling drenching at planting. The isolates were characterized, based on macro-morphological and biochemical traits, and mechanisms involved in Plant Growth-Promoting (PGP) features were explored. For direct PGP traits, isolates were able to fix nitrogen on N-free agar medium. Isolates B45, B46, B54 and B55 were positive for indole-3-acetic acid production; isolates B46, B48 and B55 were positive for phosphate solubilization with the highest activity exhibited by B46. For indirect PGP traits, isolates were chitinase-, lipase-, and amylase-producing agents. Based on phylogenetic analysis of the 16S rDNA, the most bioactive isolate B46 was affiliated to Bacillus vallismortis (OK083726). All isolates displayed antifungal activity against soil-borne fungi Aspergillus niger, Penicillium digitatum, Fusarium oxysporum, F.sambucinum, and Trichoderma harzianum. Fodder radish aqueous extracts were tested at 5, 7.5, 10 or 15% (w:v). Chemical characterization by spectrophotometer of compounds indicated presence of auxin and polyphenols. Fodder radish aqueous extract displayed antifungal activity against all fungal species. Fodder radish appears to be a natural source for isolation of potent PGP rhizobacterial isolates and/or secondary metabolites bioactive for promotion of tomato growth and with an antifungal potential.

Identification and in vitro Characterization of Plant Growth-promoting Pseudomonas spp. Isolated from the Rhizosphere of Tomato (Lycopersicum esculentum) Plants in Kenya

The rhizosphere is a rich environment for microbial communities and plays a crucial role in many plant-microbe interactions. This research aimed to isolate, identify, and in vitro characterize plant growth-promoting Pseudomonas species from the rhizosphere of field-grown tomato plants. Twenty-five soil samples were taken from tomato plants grown under various management conditions, isolated with population densities greater than 104 cells g-1 and obtained from N-free semisolid media. Important plant growth-promoting processes in vitro were identified and defined in the ten bacterial strains, which were then phylogenetically classed. Screening for their PGP properties revealed that seven (18%) isolates exhibited nitrogen-fixing ability in solid medium, nine (24%) isolates were able to solubilize phosphate, and five (13%) isolates were able to produce hydrogen cyanide. Only one isolate (3%) was capable of synthesizing IAA. The maximum potassium solubilization was achieved in KCl (16%) and K₂SO₄ (13%). The isolates showed more comprehensive levels of tolerance to pH (5 to 9), temperature (20℃ to 40℃), and salt (0% to 15%). Based on this, rhizobacterial isolates with numerous plant growth-promoting potentials were discovered based on their 16S rRNA gene sequencing, and the phylogenetic analysis of the isolates was evaluated, and all selected isolates as being similar to members of the genus Pseudomonas spp. Therefore, based on the plant growth-promoting properties assessed in vitro, the selected bacterial isolates have the potential to boost plant growth and biofertilizer production.

Bacillus tequilensis PKDN31 and Bacillus licheniformis PKDL10 –As double headed swords to combat Fusarium oxysporum f. sp. lycopersici induced tomato wilt

Wilt disease, caused by Fusarium oxysporum. f. sp. lycopersici, is a global threat to tomato production that needs to be addressed seriously. The current research envisages the use of two self-compatible Bacillus strains, Bacillus tequilensis PKDN31 and Bacillus licheniformis PKDL10, in a combinatorial approach. The spent supernatant of liquid cultures from strains PKDN31 and PKDL10 showed in vitro antifungal activity against Fusarium sp. attaining an inhibition percentage of 95.33% and 96.54%, respectively. The bacterial isolates lytic activity against Fusarium oxysporum was evaluated by scanning electron microscopic analysis and lytic enzyme production of amylase, lipase, protease and β-1,3 glucanase. Furthermore, PKDN31 and PKDL10 produced siderophores and had root colonizing ability that enhanced the biocontrol efficiency. Combined in vivo inoculation of Bacillus tequilensis PKDN31 and Bacillus licheniformis PKDL10 on tomato seeds revealed that the strains could induce systemic resistance in tomato against Fusarium oxysporum. f. sp. lycopersici by increasing defence enzymes such as β-1,3 glucanase, polyphenol oxidase, peroxidase, phenylalanine ammonia-lyase, chitinase, and total phenol accumulations. Pot culture experiments also proved the biocontrol efficacy of the above dual culture supplementation as this treatment displayed a better growth as well as defense against Fusarium challenge compared to the controls. The obtained results suggest that rhizobacterial isolates could be employed as systemic resistance inducers and biocontrol agents in tomato plants to protect against Fusarium wilt disease.