Influence of beneficial microbial interactions on morphological traits of plants

Introduction

Green gram (Vigna radiata L.) is one of the most important short-duration pulse crops cultivated across tropical and subtropical regions, particularly in South and Southeast Asia. In India, it occupies a prominent position among grain legumes due to its high protein content (22-24%), digestibility, low input requirement, and suitability for diverse cropping systems. Major green gram-growing states include Rajasthan, Maharashtra, Andhra Pradesh, Telangana, Karnataka, Madhya Pradesh, Tamil Nadu, Odisha, and Uttar Pradesh. Owing to its short life cycle and adaptability, green gram is widely grown during kharif, rabi, and summer seasons, contributing significantly to nutritional security and soil fertility through biological nitrogen fixation. Despite its agronomic and nutritional importance, the productivity of green gram remains relatively low compared to its potential yield. The national average productivity is constrained by several factors, including poor soil fertility, erratic rainfall, drought stress, inadequate nutrient availability, low responsiveness to chemical fertilizers, and limited use of highperforming bio-inputs. Morphological traits such as plant height, shoot and root growth, biomass accumulation, leaf area development, and branching pattern play a crucial role in determining crop establishment, light interception, nutrient uptake, and final yield. Any adverse impact on early vegetative growth directly translates into reduced productivity. In recent years, the use of beneficial microbial inoculants, particularly Rhizobium and plant growth-promoting rhizobacteria (PGPR), has emerged as an eco-friendly and sustainable strategy to enhance crop growth. These microorganisms influence plant morphology through multiple mechanisms, including biological nitrogen fixation, solubilization of nutrients, production of phytohormones (such as auxins, gibberellins, and cytokinins), enhancement of root architecture, and improvement of soil-root interactions. Enhanced root length, root biomass, shoot growth, and overall plant vigour resulting from microbial inoculation are critical for efficient water and nutrient acquisition, especially under sub-optimal soil conditions.

The effectiveness of microbial inoculation, however, largely depends on the selection of efficient and compatible strains or consortia that can successfully colonize the rhizosphere and express plant growth-promoting traits. The need of the hour is to identify and evaluate efficient microbial strains and strain combinations that consistently improve morphological attributes of green gram across growth stages. Such improvements not only enhance early crop establishment but also provide a strong foundation for improved physiological functioning and yield realization. Therefore, the present study focuses on evaluating the morphological influence of microbial inoculants on plant growth traits of green gram, including plant height, shoot and root length, fresh and dry biomass, leaf area, stem thickness, and branching pattern. Understanding the extent to which selected microbial strains and consortia modulate these growth attributes is essential for developing effective bio-inoculant strategies aimed at sustainable green gram production.

Materials and Methods

The present pot culture experiment was conducted at green house conditions during February 2024-April 2024, this particular season was selected because during this period environmental conditions were much similar to paddy fallows in farmers' fields where higher temperature and moisture stress conditions were seen. By evaluating the consortium in similar conditions, under pot culture there will be selection of effective consortium suitable to actual field can be done. The environmental parameters were collected from records of agricultural meteorology department recorded during February to April as follows The treatments of the present study were designed after a series of plant growth promoting traits. At 30, 45 and 60 DAS, plants were uprooted to examine complete plant height. Plant height was measured from base of the plant (root tip) up to the tip of the fully opened top leaf. The mean values were expressed in centimeter. Dry weight of shoot and root were recorded at 30, 45 and 60 DAS after separating the shoot from root. For dry weight the samples were dried at 75 °C until there was no reduction in weight and the mean values were expressed in gram per plant. The leaf area of plants was measured using graph sheets and area was recorded. The mean values were expressed in centimeters. The stem width of plants was measured using vernier caliper scale at ground level of shoot and the mean values were expressed in centimeters. The branches from plants of each treatment's replications were manually counted and the average of this was noted as the number of branches per plant

Results

The observations on plant height were recorded at 30, 45 and 60 DAS in triplicates and the results are presented in Table

Leaf area

The leaf area of all treatments were assessed using graph sheets at 45 DAS and the results are presented in Table 4. Inoculation of consortium for green gram varieties, increased the leaf area of green gram significantly as compared to controls. Among all observation recorded across all different treatments, microbial consortium with M7 inoculum shown highest leaf area (81.25) in centimeters followed by M5(71.34), M6(68.29) when compared to other treatments and least leaf area among all treatments was shown by uninoculated control (M9) with a value of 37.75 cm whereas, M1 inoculum with NC-92 showed leaf area of 41.75cm. Among the varieties, DGGV-2 with an average of 58.88 shown higher leaf area in centimeters when compared to DGG-96 (51.22) at 45 DAS. The interaction effect of Rhizobium and rhizobacteria for varieties DGGV-2 andDGG-96 was found significant at 45 DAS with a range of 90.00-35.92 cm. The treatment M7 with DGGV-2 recorded significantly highest leaf surface area at 45 DAS with value of 90.00 cm.

Stem width

The stem width of treatments was measured using vernier caliper at 45 DAS and the results are presented in (Table 4). Inoculation of consortium for green gram varieties, increased the stem width of green gram significantly as compared to controls. Among all observation recorded across all different treatments, microbial consortium with M7 inoculum (1.88) shown highest stem width in centimeters when compared to other treatments followed by M5 inoculum (1.78), M6 inoculum (1.73) and least stem width among all treatments was shown by M9 inoculum (1.18) whereas, M1 inoculum with NC-92 showed stem width of 1.45 cm. Among the varieties, DGGV-2 with an average of 1.63 shown higher stem width in centimeters when compared to DGG-96(1.58) at 45 DAS. The interaction effect of microbial inoculum with varieties DGGV-2 and DGG-96 was found significant in stem width at 45 DAS with a range of 1.90-1.13cm. The treatment M7 with DGGV-2 recorded significantly highest stem width in centimeters 1.90 at 45 DAS.

Number of branches per plant

Number of branches per plant were counted manually at 45 DAS and the results are presented. (Table 4) Inoculation of consortium for green gram varieties, increased the no. of branches of green gram significantly as compared to controls. Among all observation recorded across all different treatments, microbial consortium with M7 inoculum (8.80) shown highest no. of branches when compared to all treatments followed by M5 inoculum (7.25), M6 inoculum (6.80) and least no. of branches among other treatments was shown by M9 inoculum (4.65) whereas, M1 inoculum with NC-92 showed number of branches per plant of 5.21cm. Among the varieties, DGGV-2 with an average of 6.40 shown higher no. of branches when compared to DGG-96 (5.83) at 45 DAS. The interaction effect of microbial inoculum with varieties DGGV-2 and DGG-96 was found significant in number of branches per plant at 45DAS with a range of 9.00-4.30. The treatment M7 with DGGV-2 recorded significantly higher no. of branches per plant 9.00 at 45 DAS

Discussion

The consortia were evaluated in terms of plant growth promotion with host crop as green gram. Green gram varieties DGGV-2 which is a ruling variety, most suitable for paddy fallow along and susceptible for green gram yellow mosaic virus and DGG-96 (pipeline variety) with resistance to green gram yellow mosaic virus, anthracnose disease were selected for pot culture studies. The experiment consisted inoculation of NC-92 The using microbial inoculants for green gram variety as significantly increased plant growth in terms of overall plant height, shoot length, root length, shoot fresh and dry weight, root fresh and dry weight, Microbial consortium inoculation to green gram varieties has significantly increased Plant height, shoot length, root length, number of branches per plant when compared to positive controls (NC-92, HR-73, BR-29) and uninoculated control at 30,45,60 DAS. The increased vegetative parameters then comparted to controls could be due to synergistic effects of consortium and synthesis of phytohormones like auxin and antagonistic activity against pathogenic microorganism. The results revealed that vegetative parameters (Plant height) when observed at 30,45 and 60 DAS were highest for DGGV-2 then DGG-96 among the varieties and among microbial inoculum plants with M7 (HR-73+ BR-29+ AUDP 203 + AUDP 279) treatment shown highest vegetative parameters. The interaction effect of Rhizobium and rhizobacteria was positively corelated in green gram varieties. Interaction effect in DGGV-2 variety with M7 treatment shown highest vegetative parameters in overall when compared to all other treatments because of synergistic effects of consortia promoted overall vegetative parameters.

Green gram being an annual crop the highest vegetative parameters were recorded at 45 DAS because of its plants were entered to flowering and just stared pod filling indicating the completion of vegetative stage. These findings are in similar with Tejasree et al. (2024) [3] who reported that seed biopriming with bacterial consortia in green gram at Maharashtra has significantly improved average plant height (65.66 cm), average number of leaves per plant (22.79), average number of branches (5.23), average number of pods per plant (30.93). Mir et al.

(2024) [2] conducted a greenhouse experiment at Osmania University, Hyderabad using Rhizobium sps (as Rhizobium tropici IHTF1 and Rhizobium mayense IHTF-2) and reported that two strains, exhibit superior PGP traits in Phaseolus vulgaris with both individual and consortium mode of inoculations. Root, shoot length and fresh and dry biomass were increased in inoculated plants when compared to non-inoculated control plants.

Plant parameters like shoot dry weight and root dry weight, stem width showed significant differences at 30,45 and 60 DAS.

Inoculating seeds with efficient consortium will promote the mobilization of nutrients. When plants were inoculated with AUDP 203 and AUDP 279 which are proven nutrient (N, P, K, Zn) solubilizing and mobilizing strains enhances nutrient availability for plant and contributes for growth promotion and plant health management. On the other hand, efficient Rhizobium strain establishes symbiotic relationship with host plants and fixes atmospheric N 2 to NH 3 . Ammonia will be utilized by plants for metabolic activity.

The environment parameters like Temperature, availability of moisture, Relative humidity will significantly affect plant growth promotion. According to Van't Hoff's rule increase in every 10 °C will double the metabolic rate; plant exposed to higher temperatures under optimum conditions will increase the metabolic activities. When adequate nutrients are available for plant growth along with sufficient moisture content, increase in temperature will result in better yields. Green gram being able to grow between temperatures 15 0 to 40 °C was positively responded when they grown during February to April with an temperature range of 17.0-37. [1] who reported that inoculation of Rhizobium in Kenya has increased shoot dry biomass (52.01 g/plant), root dry biomass (7.60 g/plant), total dry biomass (146.4 g/plant), number of pods (84/plant) and yield (2158 kg/ha). Musyoka et al. (2020) [5] conducted a pot experiment in Kenya and reported coinoculation of Bradyrhizobium and arbuscular mycorrhizal fungi (AMF) significantly enhanced shoot and root dry weights as well as phosphorus content compared to Bradyrhizobium alone and control plants. across all watering regimes. Singh et al.

(2022) [4] conducted a field experiment in Uttar Pradesh and reported that applying NPK Consortia and Zinc Solubilizing Bacteria (ZSB) at rate of 20ml/kg on Mung Bean (Vigna radiata L.) resulted in the highest plant density (331229 plants/ha), tallest plants (67.7 cm/plant), most trifoliate leaves per plant (12.7), highest number of branches per plant (4.5), greatest dry matter accumulation per plant (18.7 g/plant), highest leaf area index (5.72), and fastest crop growth rate (7.6 g/m 2 /day) at harvest. This treatment also yielded the highest grain production at 1106 kg/ha, and led to a 59.8% increase in dry matter accumulation per plant compared to the control. Kumar et al.

(2023) [6] conducted experiment in Tamil Nadu and reported that inoculation of Rhizobium mayense sps.nov, to finger millet (Eleusine coracana) and green gram (Vigna radiata) under pot conditions has increased the total plant growth and dry weight compared to the control. The chlorophyll content of green gram and finger millet was estimated to be 19.54±0.2784 mg/L and 15.3±0.0035 mg/L which suggested that Rhizobium sps. possesses high nitrogenase activity.

Conclusion

The findings of this study demonstrate that inoculation with Rhizobium and rhizobacteria significantly enhances plant growth parameters of green gram. Microbial consortia were more effective than single inoculants in promoting plant height, branching, root development, and biomass accumulation. The improved growth response can be attributed to synergistic microbial interactions that enhance nutrient uptake and stimulate plant physiological processes. These results emphasize the importance of consortium-based bioinoculants in improving vegetative growth and crop establishment. Further validation under field conditions will help in translating these benefits into practical applications for sustainable pulse cultivation.

Acknowledgement

AcknowledgmentsI am extremely grateful to AICRP on EAAI (Bioconversion Technology) for timely issuing materials, chemical and assistance whenever required.

References

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