Mungbean Rhizosphere Research Articles

Bacterial inoculants as effective agents in minimizing the non-target impact of azadirachtin pesticide and promoting plant growth of Vigna radiata.

Microbes regulate soil health by negating ecological disturbances, and improve plant productivity in a sustainable manner. Indiscriminate application of pesticides creates a detrimental impact on the rhizospheric microbiota, thereby affecting soil health. Azadirachtin, earlier believed to be an environment-friendly alternative to chemical pesticides, exhibits a non-target impact on microbial communities. This study aimed to employ potent bacteria to promote the growth of mungbean plant (Vigna radiata), and mitigate the non-target impact of azadirachtin. Bacterial strains were isolated by enrichment from mungbean rhizosphere. A plant growth experiment was performed with mungbean, amended with azadirachtin to assess the impact of bacterial bioinoculants on the rhizospheric microbiota. The impact of azadirachtin on rhizospheric bacterial community was analyzed qualitatively and quantitatively by 16S rRNA PCR-DGGE and qPCR of various markers, respectively. Residual concentration of azadirachtin in the soil was estimated by HPLC. The bacterial inoculants used in combination significantly promoted plant growth and enhanced the diversity and abundance of total bacterial community in the presence of azadirachtin. Further, the abundance of specific bacterial groups (α-Proteobacteria, β-Proteobacteria, Actinobacteria, Acidobacteria, and Firmicutes) were significantly boosted. Compared to the control, the isolates significantly facilitated the reduction in residual concentration of azadirachtin in the mungbean rhizosphere. Bacterial inoculants can serve a tripartite role in reducing the stress imparted by botanical pesticides, together with promoting plant growth and enriching the rhizospheric bacterial community structure.

Burkholderia cepacia BAM-12 isolated from mungbean field in Rajasthan augments plant growth in agricultural field soil of Gujarat, India

Application of exotic bacterial strains as biofertilizer has always posed a constraint in the success of biofertilizer technology. Only a limited number of biofertilizers with applicability in a wide range of soil conditions is available in the market. Pseudomonas cepacia BAM-12 (MTCC No. 7100) (now known as Burkholderia cepacia), an isolate from the mungbean rhizosphere of the agricultural field of Rajasthan has shown remarkable plant growth promotion in Gujarat agricultural field soil. B. cepacia was found to increase the overall growth of 3 agriculturally important plants widely grown in Gujarat region, viz., mungbean, maize and rice. Increased plant growth was assessed on the basis of increased leaf number and area, biomass, chlorophyll content, profuse adventitious root branching, increased nodulation (in mungbean only), high available P in soil and overall plant growth in B. cepacia treated plants. Vital factor towards increased plant growth was the amount of IAA secreted by the organism (i.e. 2.65 mg IAA/100 ml of the culture filtrate) which is reasonably high in comparison to earlier reports available. Furthermore, PSB has also demonstrated bioremediation potential against harmful heavy metals such as copper, lead, nickel and arsenic by tolerating upto 25 mM indicating it’s prospective in remediating heavy metal contaminated agricultural fields.

Screening of Potential Bacterial Isolates as Specific Biofertilizer Agent for Mungbean Plants

The Experiment was performed under glass house condition (24°8´ N 90°0´ E) with eight rhizobial strains namely MBR-3, MBI-5, MBI-19, MBM-4, MBM-8, MBP-10, MBB-3 and MBJ-7 obtained from mungbean rhizosphere of different locations in Bangladesh and BINA MB-1 (a registered biofertilzer for mungbean) was used as standard check along with un-inoculated control to test their potentiality under glass house condition for mungbean. Result revealed that the higher plant growth, biochemical parameters, seed yield attributes and seed yield were recorded in three bacterial isolates viz., MBI-5, MBB-3 and biofertilizer, BINA MB-1 with being the highest in MBI-5. Therefore, the isolate MBI-5 may be used as commercial biofertilizer after few more trials in the different mungbean growing areas of Bangladesh
 Res. Agric., Livest. Fish.7(2): 191-197, August 2020

Study on rhizobium interaction with osmoprotectant rhizobacteria for improving mung bean yield

Gunungkidul has calcareous soil with limitations including calcareous stone, mostly hilly terrain, and shallow cultivated layer. Furthermore, nowadays we face the disadvantages climates such as long dry seasons, a short rainy season and high temperatures caused by climate change. Climate change leads to irregular rainwater availability for microbes and crops. Research in this field is currently needed as climate change affected directly on crop production, while we need to find the strategy to keep high productivity of the plant. This research aimed to determine the ability of osmoprotectant rhizobacteria and rhizobium to support mung bean yield. Osmoprotectant rhizobacteria were isolated and screened from the calcareous soil in Gunungkidul with disadvantageous climates such as a long dry season, a short rainy season and high temperature. This research was arranged in Completely Randomized Design. The result showed that osmoprotectant rhizobacteria isolate of strain Al24-k and Ver5-k can produce 9.6306 mg g−1 cell of glycine betaine in a soil density 1.7667 x 107 CFU g−1 and 11.4870 mg g−1 cell of glycine betaine in a soil density 1.9667 x 107 CFU g−1. Inoculation of isolates osmoprotectant rhizobacteria can support mung bean yield. Osmoprotectant rhizobacteria isolate did not effect rhizobium in mung bean rhizosphere.

Native halo-tolerant plant growth promoting rhizobacteria Enterococcus and Pantoea sp. improve seed yield of Mungbean (Vigna radiata L.) under soil salinity by reducing sodium uptake and stress injury.

The beneficial microbial-plant interaction plays important role in the soil health, crop growth and productivity. Plant growth promoting rhizobacteria (PGPR) are such beneficial microorganisms, which in association with plant roots not only promote their growth but also help in counteracting the detrimental effects of soil stresses. Salt stress is one such stress, frequently confronted by the plants. The present study aimed at isolation and identification of PGPR inhabiting the mungbean rhizosphere, testing them for salt (NaCl) tolerance and subsequently in salt-supplemented mungbean crop. For this purpose, two salt-tolerant bacterial strains belonging to genus Pantoea and Enterococcus, characterized for their P-solubilization ability, indole acetic acid and siderophore production were selected. These two PGPR were further evaluated for their effect on the salt-stressed mungbean plants, grown at two salt concentrations (5 and 10dS/m). The plants treated with the combination of PGPR showed better performance in growth (16-37%) and yield (22-32%), under salt stress, as compared with control. The increasing salt concentration was found to increase the membrane damage, Na+ concentration in the plants. PGPR treatments effectively reduced the Na+ concentration (17-41%), membrane damage (1.1-1.5 folds) and enhanced the antioxidants i.e. ascorbic acid (8-26%) and glutathione (10-30%) in salt-stressed plants, in comparison to uninoculated stressed plants. Overall, the results indicated that both PGPR were effective as stress mitigators however, in combination they showed relatively better improvement in growth, yield as well as oxidative parameters of the salt-affected plants. These findings about the effects of native salt-tolerant PGPR Pantoea and Enterococcus sp. in mungbean crop are novel.

Enhancing the Mobilization of Native Phosphorus in the Mung Bean Rhizosphere Using ZnO Nanoparticles Synthesized by Soil Fungi

Phosphorus (P) is a limiting factor to plant growth and productivity in almost half of the world's arable soil, and its uptake in plants is often constrained because of its low solubility in the soil. To avoid repeated and large quantity application of rock phosphate as a P fertilizer and enhance the availability of native P acquisition by the plant root surface, in this study a biosynthesized ZnO nanoparticle was used. Zn acts as a cofactor for P-solubilizing enzymes such as phosphatase and phytase, and nano ZnO increased their activity between 84 and 108%. The level of resultant P uptake in mung bean increased by 10.8%. In addition, biosynthesized ZnO also improves plant phenology such as stem height, root volume, and biochemical indicators such as leaf protein and chlorophyll contents. In the rhizosphere, increased chlorophyll content and root volume attract microbial populations that maintain soil biological health. ICP-MS results showed ZnO nanoparticles were distributed in all plant parts, including seeds. However, the concentration of Zn was within the limit of the dietary recommendation. To the best of our knowledge, this is the first holistic study focusing on native P mobilization using ZnO nanoparticles in the life cycle of mung bean plants.

Genome Sequencing of a Mung Bean Plant Growth Promoting Strain of P. aeruginosa with Biocontrol Ability.

Pseudomonas aeruginosa PGPR2 is a mung bean rhizosphere strain that produces secondary metabolites and hydrolytic enzymes contributing to excellent antifungal activity against Macrophomina phaseolina, one of the prevalent fungal pathogens of mung bean. Genome sequencing was performed using the Ion Torrent Personal Genome Machine generating 1,354,732 reads (6,772,433 sequenced bases) achieving ~25-fold coverage of the genome. Reference genome assembly using MIRA 3.4.0 yielded 198 contigs. The draft genome of PGPR2 encoded 6803 open reading frames, of which 5314 were genes with predicted functions, 1489 were genes of known functions, and 80 were RNA-coding genes. Strain specific and core genes of P. aeruginosa PGPR2 that are relevant to rhizospheric habitat were identified by pangenome analysis. Genes involved in plant growth promoting function such as synthesis of ACC deaminase, indole-3-acetic acid, trehalose, mineral scavenging siderophores, hydrogen cyanide, chitinases, acyl homoserine lactones, acetoin, 2,3-butanediol, and phytases were identified. In addition, niche-specific genes such as phosphate solubilising 3-phytase, adhesins, pathway-specific transcriptional regulators, a diguanylate cyclase involved in cellulose synthesis, a receptor for ferrienterochelin, a DEAD/DEAH-box helicase involved in stress tolerance, chemotaxis/motility determinants, an HtpX protease, and enzymes involved in the production of a chromanone derivative with potent antifungal activity were identified.

Alleviation of drought stress in mung bean by strain Pseudomonas aeruginosa GGRJ21

Mung bean (Vigna radiata (L.) R. Wilczek), a widely cultivated pulse crops in India, experiences severe drought stress during the cultivation period. Apart from the conventional plant breeding and transgenic approaches, the application of plant growth-promoting rhizobacteria (PGPR) has always been a promising approach to improve abiotic stress tolerance in crop plants. The aim of the present study was to investigate the role of mung bean rhizosphere-associated Pseudomonas aeruginosa GGRJ21 strain on drought stress alleviation in the host plant. Fluorescent pseudomonads were isolated from mung bean rhizosphere by employing a culture-dependent approach. The role of osmotic stress tolerant P. aeruginosa GGRJ21 on drought stress alleviation in host plants was further examined in both the green house and field conditions. An elevated production of reactive oxygen species scavenging enzymes and cellular osmolytes; increased root length, shoot length, dry weight, relative water content; and a stronger upregulation of three drought stress-responsive genes, i.e., dehydration-responsive element binding protein (DREB2A), catalase (CAT1), and dehydrin (DHN) were observed in GGRJ21 inoculated plants in comparison with the uninoculated control plants tested under drought conditions. The field experimental data show an increase in biomass and better growth and development in inoculated and stressed plants when compared with untreated and stressed plants. P. aeruginosa GGRJ21 strain was found to elicit water stress tolerance in mung bean plants by accelerating the accumulation of inherent levels of antioxidant enzymes, cell osmolytes, and consistently expediting the upregulation of stress responsive genes in PGPR-treated plants under water stress conditions.

Exploitation of Rhizobacteria for Functional Traits in Mungbean

The enrichment of plant rhizosphere with beneficial bacteria is a strategy that favours the production of more vigorous seedlings, which is essential for the success of legume cultivation. The aim of this study was to select rhizobacteria that are able to act as plant growth-promoting rhizobacteria (PGPR). A total of 17 rhizobacteria belonging to genera Bacillus (8), Pseudomonas (5) and Azotobacter (4) from mungbean rhizosphere were selected on the basis of their ability to solubilize phosphate. These selected rhizobacteria were further characterized for Plant Growth Promoting (PGP) traits for quantitative phosphate solubilisation, Indole Acetic Acid (IAA), organic acid production and Intrinsic antibiotic spectra (IAR), control of phytopathogen via siderophore and cellulase production and stress tolerant management by 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Significantly high phosphate was solubilized by strain of Bacillus sp. B2 (9.77 mg ml−100) followed by strain of Pseudomonas sp. P10 (9.14 mg ml−100) and strain of Azotobacter sp. A3 (8.98 mg ml−100). In the presence of L-trptophan P10, A3 and B2 were also able to produce significant high amount of IAA i.e. 55.6 μg ml−1, 52.6 μg ml−1 and 50.3 μg ml−1 respectively and they also produced organic acid, siderophore and cellulase. Of 17 rhizobacterial isolates, 11 were found compatible with Rhizobium sp. vigna (LSMR1) in-vitro. IAR pattern revealed 52.9% of rhizobacteria resistant to ampicillin (10 μg disc−1) and chloramphenicol (25 μg disc−1). ACC deaminase activity was measured by their growth in DF medium supplemented with ACC (OD 600 ranged from 0.117 to 0.432) as nitrogen (N) source. In the present investigation, rhizobacterial isolates viz, B2, P10 and A3 were found most promising for multiple activities (PGP traits, biocontrol and stress tolerant activities) and can be evaluated in-vivo for their possible role in mungbean growth and development.

Biocontrol features in an indigenous bacterial strain isolated from agricultural soil of Gujarat, India

The present investigation was carried out to test the biocontrol potential of a phos- phate solubilizing bacterial strain, LK11 isolated from mungbean rhizosphere, in Gujarat, India. This strain besides solubilizing the insoluble P also demonstrated in- hibition of Sclerotium rolfsii growth in agar plate and produced a volatile compound, HCN. During in vitro studies LK11 inhibited sclerotia germination by 40%. The most important contributing factor towards increased mungbean growth by reduc- ing fungal attack was the enhanced production of antifungal compounds like PAL (47 mM/ml/mg of tissue), phenolics (90.2 µg/ml/mg) and flavonoids (184.2 mg/ ml/g) which is comparable to earlier reports available. Testing the efficiency of this strain in consortium culture alongwith some other PGPR strains and biocontrol mi- crobes at multilocational fields is in offing.

Impact of biocontrol agents Pseudomonas fluorescens CHA0 and its genetically modified derivatives on the diversity of culturable fungi in the rhizosphere of mungbean.

To assess whether Pseudomonas fluorescens strain CHA0 and its genetically modified derivatives, CHA0/pME3424 (antibiotic over-producer) and CHA89 (antibiotic-deficient) could have an impact on the fungal community structure and composition in the rhizosphere of mungbean. Under glasshouse conditions, mungbean was grown repeatedly in the same soil, which was inoculated with CHA0, CHA0/pME3424, CHA89 or was left untreated. Treatments were applied to soil at the start of each 36-day mungbean growth cycle, and their effects on the diversity of the rhizosphere populations of culturable fungi were assessed at the end of the first, second and third cycles. The effects of CHA0 and CHA0/pME3424 did differ from the controls while CHA89 did not. Whereas all major fungal species were frequently isolated from both bacterized and nonbacterized rhizospheres, certain fungal species were exclusively promoted or specifically suppressed from Pseudomonas-treated soils. In general, fungal diversity and equitability tended to decrease with time while species richness slightly increased. Whilst a total of 29 fungal species were isolated from the mungbean rhizosphere, only eight species colonized the root tissues. Soil inoculation with Ps. fluorescens CHA0 or CHA0/pME3424 altered fungal community structure in mungbean rhizosphere but strain CHA89 failed to produce such effect. Pseudomonas fluorescens-mediated alteration in the composition and structure of fungal communities might have acute or lasting effects on ecosystem functioning. Furthermore, the study provides useful data pertinent to characterization of the fate of genetically modified inoculants (e.g. antibiotic-overproducing Pseudomonas strains) released into the environment.

Plant Species, Host Age and Host Genotype Effects on Meloidogyne incognita Biocontrol by Pseudomonas fluorescens Strain CHA0 and its Genetically‐Modified Derivatives

Abstract Pseudomonas fluorescens strain CHA0 and its antibiotic overproducing derivative CHA0/pME3424 repeatedly reduced Meloidogyne incognita galling on tomato, brinjal, mungbean and soya bean roots but not in chilli. An antibiotic‐deficient derivative, CHA89, did not reduce nematode invasion in any of the plant species tested. When plant species were compared, bacterial inoculants afforded better protection to tomato, mungbean and soya bean roots against root‐knot nematodes than to brinjal and chilli. Antibiotic overproducing strain CHA0/pME3424 markedly reduced fresh shoot weights of chilli and mungbean while antibiotic‐deficient strain CHA89 enhanced fresh shoot weights of mungbean. While strains CHA0 had no significant impact on fresh root weights of any of the plant species, strain CHA0/pME3424 consistently reduced fresh root weights of brinjal and mungbean. In none of the plant species the bacterial strains had an influence on protein contents of the leaves. Regardless of the plant species, the three bacterial strains did not differ markedly in their rhizosphere colonization pattern. However, colonization was highest in brinjal rhizosphere and lowest in the mungbean rhizosphere. A slight host genotype effect on the biocontrol performance of the bacterial inoculants was also detected at cultivar level. When five soya bean cultivars were compared, biocontrol bacteria exhibited best suppression of the root‐knot nematode in cv. Ajmeri. Antibiotic overproducing strain CHA0/pME3424 substantially reduced fresh shoot weights of the soya bean cultivars Centuray 84 and NARC‐I while strain CHA89 enhanced shoot weights of the cultivars Ajmeri, William‐82 and NARC‐II. Wild type strain CHA0 had no significant impact on fresh shoot weights of any of the soya bean cultivars. Strain CHA0/pME3424 reduced fresh weights of root of Century 84, NARC‐I and NARC‐II while strain CHA89 increased root weights. Bacterial rhizosphere colonization was highest in variety NARC‐I and lowest in variety Ajmeri. Plant age had a significant impact on the biocontrol performance of bacterial inoculants against nematodes. The biocontrol effect of all bacterial strains was more prominent during early growth stage (7 days after nematode inoculation). A strong negative correlation between bacterial rhizosphere colonization and nematode invasion in soya bean roots was observed.

Improvement of Pseudomonas fluorescens CHA0 biocontrol activity against root-knot nematode by the addition of ammonium molybdate.

To improve the efficacy of Pseudomonas fluorescens CHA0 and its genetically modified (GM) derivatives by adding ammonium molybdate to control Meloidogyne javanica, the root-knot nematode in mungbean. Culture filtrate of P. fluorescens CHA0 and its GM derivative (antibiotic overproducing strain CHA0/pME3424 and antibiotic-deficient CHA89) obtained from nutrient broth yeast extract medium amended with 1, 2 or 4 mm of ammonium molybdate (NH4-Mo) caused substantial mortality of M. javanica juveniles in vitro. Pseudomonas fluorescens CHA0 or CHA0/pME3424 applied in conjunction with NH4-Mo caused greater reduction of nematode penetration in mungbean roots compared with the bacterial application alone. Ammonium molybdate at 4 mg kg-1 of soil along with CHA0 also enhanced plant height while shoot weight remained unaffected. Either used alone or in conjunction with NH4-Mo, strain CHA89 did not reduce nematode invasion compared with the controls. Bacterial strains did not differ significantly in their colonization potential in the mungbean rhizosphere. Efficacy of the biocontrol bacteria to control root-knot nematode was accentuated when soil was treated with NH4-Mo and zinc (both at 1 mg kg-1 of soil). The addition of ammonium molybdate enhances the production of nematicidal compounds by P. fluorescensin vitro and improves bacterial efficacy against root-knot nematode under glasshouse conditions. Application of minerals such as ammonium molybdate is appealing because they are cheap and can easily be applied under field conditions to improve biocontrol potential of the bacterial inoculants. They also significantly reduce the amount of biocontrol inoculant biomass required to achieve root-knot disease control, with a consequent reduction in cost.