Evaluation of efficient Rhizobium spp. and Pseudomonas spp. on growth and biomass of green gram under pot culture conditions

Introduction

Green gram (Vigna radiata L.) is an important short-duration pulse crop widely cultivated for its nutritional value and adaptability to diverse agro-climatic conditions. Its relatively short growth duration makes it suitable for intensive and multiple cropping systems. However, maintaining crop productivity with reduced dependence on chemical fertilizers is an important aspect of sustainable crop production. Beneficial microorganisms can contribute to improved nutrient availability and plant growth and may support efficient fertilizer use. Rhizobium forms symbiotic associations with leguminous plants and plays an important role in biological nitrogen fixation. They colonize compatible roots and induce the formation of root nodules, where atmospheric nitrogen is converted into a form that can be utilized by the plant. Efficient rhizobial inoculation can consequently improve nitrogen nutrition, nodulation and plant biomass. The effectiveness of inoculation may vary among bacterial strains, making the selection of efficient isolates important for crop production. Pseudomonas are important rhizosphere-associated plant growth-promoting bacteria that can contribute to plant development through several mechanisms, including phosphate solubilization, production of growthpromoting substances and improvement of nutrient availability. Their application in combination with Rhizobium may provide complementary benefits by enhancing nutrient uptake, root development and overall plant growth. Although efficient microbial isolates may exhibit promising plant growth-promoting characteristics in vitro, their effectiveness must be evaluated under actual plant-growing conditions. Therefore, the present study was undertaken to evaluate the potential of efficient Rhizobium spp. and Pseudomonas spp. isolates, individually and in combination with 75% RDF, for enhancing growth and biomass of green gram under pot culture conditions.

Material and Methods

Pot culture experiment

A pot culture experiment was conducted at the College of Agriculture, UAS, Raichur, to evaluate the effect of efficient Rhizobium and Pseudomonas isolates on the growth and biomass of green gram. The BGS-9 variety of green gram was used for the experiment. Pots containing 5 kg of normal black soil were used. Seeds were treated with respective microbial inoculants before sowing. The experiment was laid out in a Completely Randomized Design (CRD).

Selection of efficient isolates

Based on the earlier in vitro screening, GRL-11 was selected as the efficient Rhizobium isolate and GPL-7 as the Pseudomonas isolate for evaluation under pot culture conditions.

Recording of observations

Plant height, root length, number of branches, total dry weight, number of pods per plant and number of seeds per pod were recorded at harvest. Number of nodules and nodule dry weight were recorded at 45 DAS. Chlorophyll content was recorded as SPAD values at 30 DAS, 60 DAS and at harvest. The total microbial population in the rhizosphere soil was recorded at 30 DAS, 60 DAS and at harvest and expressed as ×10 7 CFU g -1 soil.

Treatments

Statistical analysis

The experimental data were statistically analyzed and treatment differences were assessed using S.Em. ± and CD at 1% level as presented in the respective tables.

Results and Discussion

Plant height and root length

Significant differences in plant height were observed among the treatments at harvest (Table 1). Treatment T7 (75% RDF + GRL-11 + GPL-7) recorded the highest plant height (51.86 cm), whereas the lowest value (39.28 cm) was recorded in T2 (75% RDF). Root length also differed significantly among treatments (Table 1). T7 recorded the maximum root length (18.64 cm) at harvest, while T2 recorded the minimum value (13.56 cm).

The greater plant height under combined inoculation may be attributed to the complementary activities of Rhizobium and Pseudomonas, which can improve nitrogen availability, nutrient acquisition and production of growth-promoting substances. The present findings are supported by Ahmad et al. [1] , who reported that co-inoculation of Rhizobium and Pseudomonas increased plant height of mung bean by up to 21 % compared with the uninoculated control. Enhanced root development may be associated with improved nutrient availability and growth-promoting activities of the inoculated microorganisms, thereby enhancing water and nutrient uptake and shoot growth. Similar enhancement in root length following Rhizobium-Pseudomonas co-inoculation was reported by Verma et al. [2] .

Number of branches and total dry weight

The number of branches per plant varied significantly among treatments (Table 1). T7 recorded the highest number of branches at harvest (11.20), whereas T2 recorded the lowest (8.37). A significant variation in total dry weight was also observed among the treatments (Table 1). T7 recorded the highest dry weight (12.17 g plant -1

) at harvest, while T2 recorded the lowest (8.74 g plant -1 ). The increased branching under combined inoculation may be related to improved nitrogen nutrition and the plant growth-promoting activities of the inoculated bacteria. Comparable enhancement in the number of branches following Rhizobium-Pseudomonas co-inoculation was reported by Netwal et al. [3] . The higher biomass accumulation under combined inoculation may be associated with improved nodulation, nitrogen fixation, nutrient availability and root development. Ahmad et al. [1] also reported increased total dry matter of mung bean following co-inoculation.

Nodulation and nodule dry weight

Significant differences in nodulation were observed among the treatments (Table 2). At 45 DAS, T7 recorded the highest number of nodules (32.74 plant -1 ), whereas T1 (100% RDF) recorded the lowest (16.14 plant -1 ). Nodule dry weight followed a similar trend. T7 recorded the highest nodule dry weight (42.37 mg plant -1 ), whereas the lowest value was recorded in T1 (24.76 mg plant -1 ). The higher nodulation in T7 may be attributed primarily to the efficient Rhizobium isolate GRL-11, which established an effective symbiotic association with green gram roots. The additional contribution of Pseudomonas may have supported rhizobial establishment and root development through its plant growth-promoting activities. Similar increase in nodulation through Rhizobium-Pseudomonas co-inoculation has been reported by Ahmad et al. [1] . The increase in nodule dry weight can be attributed to Rhizobium inoculation, which establishes a symbiotic association with green gram roots. These findings are similar to the reports of Selvakumar et al. [4] and (Khan and Prakash) [5] .

Number of pods and seeds per pod

The number of pods per plant differed among treatments (Table 2). T7 recorded the highest number of pods (17.87 plant -1 ), while T2 recorded the lowest (10.33 plant -1 ). The number of seeds per pod also varied among treatments. T7 recorded the highest value (10.62 seeds pod -1 ), whereas T2 recorded the lowest (7.33 seeds pod -1 ). The increase in pod formation under combined inoculation may be associated with improved vegetative growth, nodulation, nitrogen fixation and nutrient availability. Yadegari et al. [6] reported a similar improvement in the number of pods per plant following Rhizobium + Pseudomonas co-inoculation in common bean. Improved nitrogen and phosphorus availability through microbial activity may have supported flower retention, pod development and seed setting. Similar yield components following combined inoculation with Rhizobium and Pseudomonas have been reported by Ahmad et al. [1] .

Chlorophyll content and rhizosphere microbial population

Significant differences in chlorophyll content were observed among treatments (Table 3). T7 recorded the highest chlorophyll content at 30 DAS (44.72 SPAD), 60 DAS (50.16 SPAD) and harvest (46.74 SPAD), whereas T2 recorded the lowest values of 34.60, 38.12 and 36.41 SPAD, respectively. Significant differences in the rhizosphere microbial population were also observed among treatments (Table 3). T7 recorded the highest microbial population at 30 DAS (32.34 × 10 7 CFU g -1 soil), 60 DAS (43.76 × 10 7 CFU g -1 soil) and harvest (31.48 × 10 7 CFU g -1 soil). T2 recorded the lowest populations of 13.83, 19.35 and 12.68 × 10 7 CFU g -1 soil, respectively. The higher chlorophyll content under combined inoculation may be associated with improved nitrogen availability through biological nitrogen fixation and enhanced nutrient acquisition. Nitrogen is an important component of chlorophyll and therefore improved nitrogen nutrition may contribute to greater chlorophyll formation and photosynthetic activity. Ahmad et al. [1] reported that co-inoculation of Rhizobium phaseoli and Pseudomonas strains significantly improved chlorophyll content, photosynthetic activity and physiological performance of mung bean under salt-affected conditions. The higher microbial population under T7 indicates better establishment and proliferation of the inoculated microorganisms in the green gram rhizosphere. Increased root growth and availability of root-derived organic compounds may have supported microbial colonization and multiplication. Shravani et al. [7] also reported higher bacterial populations in the rhizosphere of mungbean following biofertilizer application.

Conclusion

The pot culture experiment demonstrated that inoculation with efficient Rhizobium spp. and Pseudomonas spp. isolates positively influenced the growth and performance of green gram. Among the treat-ments, T7 (75% RDF + GRL-11 + GPL-7) consistently recorded superior values for plant height, root length, number of branches, total dry weight, nodulation, nodule dry weight, number of pods, seeds per pod, chlorophyll content and rhizosphere microbial population. The combined application of GRL-11 and GPL-7 with 75% RDF therefore showed better performance than 75% RDF alone and individual microbial inoculation treatments. These findings indicate that the efficient Rhizobium spp. and Pseudomonas spp. isolates, particularly their combined application, have potential to improve green gram growth and productivity under pot culture conditions.

Acknowledgements

The authors acknowledge the College of Agriculture, University of Agricultural Sciences, Raichur and the co-workers involved in the study.

References

1. Ahmad MA, Zahir ZA, Nadeem SM, Nazli F, Jamil M, Khalid M. Field evaluation of Rhizobium and Pseudomonas strains to improve growth, nodulation and yield of mung bean under salt-affected conditions. Soil Environ. 2013;32(2):158-166.
2. Verma M, Verma S, Arora NK. Application of RhizobiumPseudomonas consortia for enhanced production of mungbean in sustainable manner. Int. J. Sci. Technol. Soc. 2017;3(2):54-61.
3. Netwal M, Choudhary D, Jakhar R, Yadav B, Choudhary G. Evaluation of Indian bean (Lablab purpureus L. var. typicus) seeds inoculation with Rhizobium phaseoli and Pseudomonas fluorescens on growth, yield and nutritional quality. Int. J. Chem. Stud. 2020;8(2):2703-2707.
4. Selvakumar G, Chandrasekaran M, Shagol C, Kim KY, Sa TM. Spore associated bacteria (SAB) of arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) increase nutrient uptake and plant growth under stress conditions. Korean J. Soil Sci. Fert. 2012;45(4):582-592.
5. Khan K, Prakash V. Effect of rhizobial inoculation on growth, yield, nutrient uptake and economics of summer urdbean [Vigna mungo (L.) Hepper] in relation to zinc and molybdenum. J. Food Legumes. 2014;27(3):261-263.
6. Yadegari M, Rahmani HA, Noormohammadi G, Ayneband A. Evaluation of bean (Phaseolus vulgaris) seeds inoculation with Rhizobium phaseoli and plant growth-promoting rhizobacteria on yield and yield components. Pak. J. Biol. Sci. 2008;11(15):19351939.
7. Shravani K, Triveni S, Latha PC, Damodara Chari K. Influence of biofertilizers under drip fertigation system on soil microbial population and enzyme activities in rhizosphere of mungbean. Asian J. Microbiol. Biotechnol. Environ. Sci. 2019;21(Suppl.):S67-S72.
8. Mir MI, Kumar BK, Gopalakrishnan S, Vadlamudi S, Hameeda B. Characterization of rhizobia isolated from leguminous plants and their impact on the growth of ICCV 2 variety of chickpea (Cicer arietinum L.). Heliyon. 2021;7(11):e08321. How to cite this article: Lingaraj BP, Pampangouda, Ningappa, Yallappa M, Anupama C. Evaluation of efficient Rhizobium spp. and Pseudomonas spp. on growth and biomass of green gram under pot culture conditions. International Journal of Research in Agronomy. 2026;9(9):1231-1234. doi: https://www.doi.org/10.33