Mustard Rhizosphere Research Articles

Deciphering the Potential of Sulphur-Oxidizing Bacteria for Sulphate Production Correlating with pH Change.

Sulphur, available in the form of sulphate, is one of the essential nutrients that is required by plants. Bacteria capable of oxidizing reduced forms of sulphur to sulphate play an important role in sulphur nutrition for plants. The present study was conducted to isolate, screen, and characterize sulphur-oxidizing bacteria from different soil samples collected from mustard rhizosphere and fly ash mixed soil. A total of 33 sulphur-oxidizing bacterial isolates (HMSOB1-33) were retrieved from soil and further screened for sulphur-oxidizing ability. Maximum solubilization index (3.76), pH reduction (3.93), and sulphate production (173.61µg/ml) were observed for the isolate HMSOB2 which on the basis of 16S rDNA sequencing was identified as Pantoea dispersa with sequence similarity 98.22%. Four other selected bacterial isolates were identified as Bacillus megaterium, Bacillus tropicus, Bacillus velezensis, and Bacillus cereus. Sulphate solubilization index (SSI) correlated positively (r = 0.91) with sulphate production; however, pH showed negative correlation (r = - 0.82) with SSI as well as sulphate production after 120h of incubation. These promising bacterial isolates could be further explored as bioinoculant after assessing plant growth traits.

Molecular and phenotypic characterization of Hemicriconemoides rosae (Rathour et al., 2003) from mustard rhizosphere in India

BackgroundNematodes belonging to Genus Hemicriconemoides, commonly known as sheathoid nematodes, damaged many fruits, vegetables and cash crops, worldwide. A survey has been conducted in the agricultural fields of Bulandshahr district to find out the plant-parasitic nematodes load.ResultsA total of 85 soil samples were collected from mustard fields of Bulandshahr district of Uttar Pradesh and processed for the presence of plant-parasitic nematodes and they were isolated by ‘Cobb sieving method’. Among all the collected soil samples, one soil sample found to be positive for the genus Hemicriconemoides and docketed as HCN. The earliest identification based on morphology revealed the species to be Hemicriconemoides rosae which was recovered from the mustard field for the first time. The morphology was found to be more consistent with rose population as compared to sugarcane population of the Hemicriconemoides rosae. Further, the Hemicriconemoides rosae was identified on the basis of molecular and phylogenetic analysis based on the concatenated matrix. In addition, correlation analysis of the Hemicriconemoides rosae based on morphometric parameters was done. The results revealed the importance of body length and its relation with other morphometric parameters, and they were found significant. Besides this, de Manian index a showed highest correlation with the body length in adult females. In all the studied ratios, a is very important for the evaluation of the females of a specific species of genus Hemicriconemoides. The data from the principal component analysis (PCA) revealed the high intraspecific and interspecific variations between the species of genus Hemicriconemoides. However, less intraspecific variations were present between the rose population and mustard population of H. rosae.ConclusionsThe study revealed the new host, i.e. mustard crops, for H. rosae showing dissimilarity in morphology with the sugarcane population.

Effectiveness of Chromolaena odorata as organic manure in promoting plant nutrient uptake and soil nutrient status on mustard rhizosphere

Chromolaena odorata is an invasive plant that potentially organic manure. This study aimed to evaluate the effect of this weed on plant nutrient uptake and soil nutrient status on the mustard rhizosphere using a completely randomized block design and three replications. Factors examined were the organic manure types (green manure and compost) and doses (5, 10, 15, 20, and 25 Mg ha−1). The results showed that the compost was more effective than the green manure to improve potassium (K) uptake and soil nutrient (total nitrogen (N), available phosphor (P), and exchangeable K). Increasing doses of the organic manure until 25 mg ha−1 gave a better effect on N and K uptake and soil available P and exch. K but 20 Mg ha−1 on soil total N. The application of 25 mg ha−1 C. odorata as green manure gave more N and K content in the mustard. At the same time, 20 mg ha−1 compost increased soil available P. This study indicated that C. odorata could be developed as a good ameliorant either as green manure or compost to improve nutrient uptake mustard and soil nutrient status.

Plants Specifically Modulate the Microbiome of Root-Lesion Nematodes in the Rhizosphere, Affecting Their Fitness.

Plant-parasitic nematodes are a major constraint on agricultural production. They significantly impede crop yield. To complete their parasitism, they need to locate, disguise, and interact with plant signals exuded in the rhizosphere of the host plant. A specific subset of the soil microbiome can attach to the surface of nematodes in a specific manner. We hypothesized that host plants recruit species of microbes as helpers against attacking nematode species, and that these helpers differ among plant species. We investigated to what extend the attached microbial species are determined by plant species, their root exudates, and how these microbes affect nematodes. We conditioned the soil microbiome in the rhizosphere of different plant species, then employed culture-independent and culture-dependent methods to study microbial attachment to the cuticle of the phytonematode Pratylenchus penetrans. Community fingerprints of nematode-attached fungi and bacteria showed that the plant species govern the microbiome associated with the nematode cuticle. Bacteria isolated from the cuticle belonged to Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Sphingobacteria, and Firmicutes. The isolates Microbacterium sp. i.14, Lysobacter capsici i.17, and Alcaligenes sp. i.37 showed the highest attachment rates to the cuticle. The isolates Bacillus cereus i.24 and L. capsici i.17 significantly antagonized P. penetrans after attachment. Significantly more bacteria attached to P. penetrans in microbiome suspensions from bulk soil or oat rhizosphere compared to Ethiopian mustard rhizosphere. However, the latter caused a better suppression of the nematode. Conditioning the cuticle of P. penetrans with root exudates significantly decreased the number of Microbacterium sp. i.14 attaching to the cuticle, suggesting induced changes of the cuticle structure. These findings will lead to a more knowledge-driven exploitation of microbial antagonists of plant-parasitic nematodes for plant protection.

Biological control of mustard blight caused by Alternaria brassicae using plant growth promoting bacteria

Indian mustard (Brassica juncea) is an important oilseed crop in India. Among various diseases infecting mustard crop, Alternaria leaf spot also known as Alternaria blight is incited by fungus Alternaria brassicae, which majorly affects the crop production leading to a yield loss of up to 70 %. The disease is controlled by application of different fungicides prior to winter rains but it is costly and also cause pollution in the environment. This investigation was designed to explore the potential of rhizosphere bacteria to use as bio control agents for suppression of the disease. Total of sixteen bacterial isolates were isolated from the rhizosphere of mustard, tomato and brinjal and they were screened for their antagonistic activity against A. brassicae in vitro and in vivo conditions. Out of sixteen isolates, two bacterial isolates (B3 and B12) showed maximum inhibition (35 % and 38.6 % respectively) against the pathogen and also displayed high degree of secondary metabolite formation. These two bacterial isolates molecularly characterized as Pseudomonas fluorescens were further tested in green house and field conditions through seed bacterization treatment for disease suppression. Mustard seeds were treated with the bacterial solution overnight and were sown in pots and fields the next day. It was found that the disease incidence percentage of B3 and B12 was 32 % and 35 % respectively compared to control with 62.8 %. The results of the above study were highly significant in evaluation of PGPR against A. brassicae.

Amelioration of salinity stress and growth stimulation of mustard (Brassica juncea L.) by salt-tolerant Pseudomonas species

Indian mustard (Brassica juncea) is a winter oilseed crop grown across the Northern Indian planes. The growth and yield of the crop have been declining over the recent years due to increase in soil salinity. Applications of plant growth-promoting rhizobacterial strains have been found to enhance crop productivity under salinity conditions. Therefore, the objective of this study was to identify bacterial isolates from the mustard rhizosphere that may help in improving the mustard growth under salt stress conditions. Various plant growth-promoting activities, i.e., production of aminolevulinic acid, indole acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, and solubilization of potassium and phosphorus, were analyzed in isolated salt-tolerant rhizobacterial strains, which may contribute towards salt tolerance and crop productivity in mustard. The most promising rhizobacterial isolates HMM57 and JMM15 were identified as Pseudomonas argentinensis and P. azotoformans, respectively by 16SrRNA sequencing. In primary screening, out of ninety-four rhizobacterial isolates tested, only ten isolates HMM6, HMM13, HMM34, HMM39, HMM44, HMM57, HMM65, HMM88, JMM15 and JMM42 showed salt tolerance up to 8% NaCl concentration (0.1–20.0 mm colony size). During secondary screening on agar plates, these rhizobacterial isolates were checked for their potential to enhance seed germination of mustard and growth of seedlings at the high level of salinity (20 dS m−1). Moreover, bacterial isolates HMM57 and JMM15, which exhibited different plant growth-promoting traits, were used as inoculants on the mustard plants grown under high salinity conditions (8 and 12 dS m−1) in a greenhouse. Rhizobacterial inoculation revealed 139 to 291% increase in root and shoot dry weight even after 80 days of sowing. The results indicated that application of two potential rhizobacterial isolates HMM57, and JMM15, which were able to tolerate high salt concentration (8% NaCl) and having IAA and ALA production along with ACC utilization activities, showed stimulation of the mustard growth even up to 12 dS m−1 in plates and also under controlled greenhouse conditions. These plant growth-promoting rhizobacterial isolates may be used for the enhancement of mustard crop productivity under salinity stress and could be used as biofertilizer.

Lower Frequency and Diversity of Antibiotic-Producing Fluorescent Pseudomonads in Rhizosphere of Indian Rapeseed–Mustard (Brassica juncea L. Czern.)

Fluorescent pseudomonads are one of the most important microbial communities which play a key role in rhizosphere to enhance plant growth-promotion and protection. The diverse groups of antibiotics viz. 2,4-diacetylphloroglucinol (DAPG), phenazine-1-carboxylic acid (PCA) and pyoluteorin (PLT) are produced by fluorescent pseudomonads inhibiting growth of fungal pathogens which results in health upliftment of plants. The present study, discusses about frequency and diversity of 138 antibiotic-producing fluorescent pseudomonads isolated from eight genotypes of rapeseed mustard rhizosphere (Brassica juncea L. Czern.). The plant growth promoting traits and antibiotics (DAPG, PCA and PLT) production of isolates were examined by using polymerase chain reaction (PCR), thin layer chromatography (TLC) and dot blot-hybridization. Among 138 isolates, 47, 25 and 9 % of isolates were positive in indole production, phosphate solubilization and antagonism potential against Sclerotinia sclerotiorum (causal agent of white mold disease in rapeseed mustard), respectively. PCR amplifications showed that none of the isolates had phlD (DAPG) and phzC (PCA) genes, but four isolates (UKA-2, UKA-8, UKA-11, UKA-66) had pltB (PLT) gene, which was further confirmed by TLC and DNA dot-blot hybridization. BOX profiles of pltB positive isolates were distinct, showing unique genetic diversity in the small population. The four pltB positive fluorescent pseudomonad isolates could be used as promising bio-control and plant growth-promoting inoculants for Indian rapeseed mustard.

Enhanced Biodegradation of Mobil Oil Hydrocarbons by Biosurfactant Producing Bacterial Consortium in Wheat and Mustard Rhizosphere

Hydrocarbon fuels are one of the most common global environmental pollutants which cannot be easily degraded owing to their hydrophobic nature. The present study involves the degradation of hydrocarbons by biosurfactant producing bacterial consortia. In this study, results showed 73.66% and 75.80% degradation of 2% mobil oil hydrocarbons in contaminated soil by biosurfactant producing bacterial consortium with wheat (Triticum aestivum) and mustard (Brassica juncea) crops, respectively. Therefore, it indicates that the developed bacterial consortium are capable for the effective degradation of mobil oil hydrocarbons in wheat and mustard rhizosphere and hence can be employed effectively for the degradation of mobil oil hydrocarbons in oil contaminated soils. Phthalate esters formed during the degradation can be used for industrial applications like PVC softening.

The Study on Oil Pollution Environmental Treatment Based on Micro-Biological Degradation

All the strains screened out from contaminated soils were capable of degrading diesel oil while consortium and strains Q18 had stronger degradation efficiency. It’s found that the existence of alfalfa and mustard could promote the degradation of diesel oil significantly. The existence of plant and the growth of roots may have changed the soil environment to make it more suitable for the growth of strains and degradation. In addition, the number of strains in the mustard rhizosphere was larger than that in the alfalfa rhizosphere, which showed that mustard had stronger ability on the activation of strain. This may be related to the different growth characteristics of mustard and alfalfa. In the experiment, Rhodococcus Q18-Indian mustard complex had the highest rate of degradation of diesel oil.

Evaluation of plant-growth-promoting activities of rhizobacterium Pseudomonas putida under herbicide stress

The aim of this study was to evaluate the effect of selected herbicides (quizalafop-p-ethyl, clodinafop, metribuzin and glyphosate) at one, two and three times the recommended field rates on the plant-growth-promoting (PGP) traits of Pseudomonas putida strain PS9 isolated from the mustard rhizosphere. P. putida strain PS9 was selected for its high herbicide-tolerance and its production of substantial amounts of indole acetic acid, siderophores (salicylic acid and 2,3 dihydroxy benzoic acid) and exo-polysaccharides. It also exhibits HCN and ammonia releasing ability. A progressive, herbicide-concentration-dependent, decline in PGP properties (except exo-polysaccharide production) of P. putida strain PS9 was observed when the strain was grown in the presence of increasing concentrations of each herbicide. Generally, among the selected herbicides, the maximum toxicity to PGP traits of P. putida strain PS9 was shown by quizalafop-p-ethyl at three times the recommended dose. This study concludes that herbicides should be screened before field application for their degree of toxicity to PGP traits of beneficial microorganisms.

Effect of fungicides on plant growth promoting activities of phosphate solubilizing Pseudomonasputida isolated from mustard (Brassica compestris) rhizosphere

This study was navigated to examine the effects of fungicide-stress on the activities of plant-growth-promoting rhizobacterium Pseudomonasputida with inherent phosphate solubilizing activity. The fungicide-tolerant and phosphate solubilizing P.putida strain PS9 was isolated from the mustard rhizosphere and tentatively identified following standard morphological, physiological and biochemical tests. To further consolidate the identity of the strain PS9, the 16S rDNA sequence analysis was performed. Following the BLAST program, the strain PS9 was identified as P.putida. In the presence of the varying concentrations (0–3200μgmL−1; at a two fold dilution interval) of four fungicides of different chemical families (tebuconazole, hexaconazole, metalaxyl and kitazin) amended in minimal salt agar medium, the P.putida strain PS9 showed a variable tolerance levels (1400–3200μgmL−1) against the tested fungicides. The strain PS9 produced plant-growth-promoting (PGP) substances in significant amount in the absence of fungicides. In general, fungicides applied at the recommended, two and three times of the recommended rates, decreased the PGP attributes of P.putida the strain PS9 and affected the PGP activities in concentration-dependent manner. Fungicides at the recommended dose had minor reducing effect while the doses higher than the recommended dose significantly reduced the PGP activities (phosphate solubilization, salicylic acid, 2,3-dihydroxy benzoic acid, and indole-3-acetic acid production except exo-polysaccharides, hydrogen cyanate and ammonia production). Of the four fungicides, tebuconazole generally, showed maximum toxicity to the PGP activities of the strain PS9. This study inferred that fungicides must be examined in vitro for their possible adverse effects on soil micro flora before their application in agricultural fields. Moreover, the results also suggested the prerequisite of application of fungicide-tolerant PGPR strains as bioinoculants so that their PGP activities may not be suppressed under fungicide stress.

Biotoxic impact of fungicides on plant growth promoting activities of phosphate-solubilizing Klebsiella sp. isolated from mustard (Brassica campestris) rhizosphere

The aim of this study was to investigate the side-effects of fungicides on the physiological activities of plant growth promoting rhizobacteria with intrinsic phosphate-solubilizing potential. The fungicide-tolerant and phosphate-solubilizing bacterial strain PS19 was isolated from the mustard rhizosphere and identified as Klebsiella sp. following 16S rDNA sequencing. The Klebsiella sp. strain PS19 normally, produced plant growth promoting (PGP) substances in substantial amount. In this study, four fungicides of different chemical families (tebuconazole, hexaconazole, metalaxyl, and kitazin) at the recommended, two and three times of the recommended rates decreased the PGP attributes of the strain PS19 in fungicide-concentration dependent manner. Moreover, fungicides at the recommended dose had slight inhibitory effect while the dose higher than the recommended ones reduced the PGP traits (phosphate solubilization, salicylic acid, 2,3-dihydroxy benzoic acid, and indole-3-acetic acid production except exo-polysaccharides, hydrogen cyanate and ammonia production) significantly. Of the four fungicides, tebuconazole generally showed the maximum toxicity to the PGP activities of the strain PS19. The results of this study inferred that fungicides, which are used to control various fungal pests detrimental for the crop productivity, must be examined in vitro for their possible adverse impacts on plant-beneficial rhizobacteria before the field application. This study also revealed an additional aspect of the toxicological mechanisms of the fungicides through which they may suppress the plant growth.

Effects of insecticides on plant-growth-promoting activities of phosphate solubilizing rhizobacterium Klebsiella sp. strain PS19

In this study, four technical grade insecticides, fipronil, pyriproxyfen, imidacloprid and thiamethoxam were applied at the recommended and the higher doses to investigate their effects on plant growth-promoting activities of phosphate-solubilizing Klebsiella sp. strain PS19, isolated from mustard rhizosphere. All tested insecticides displayed a concentration-dependent inhibition in plant growth promoting traits, like, inorganic phosphate solubilization, biosynthesis of phytohormones and siderophores, of rhizobacterial strain PS19. For example, the phosphate-solubilizing activity of Klebsiella sp . PS 19 was reduced maximally by 95%, at 3900 μg l −1 pyriproxyfen over control. At the recommended rate, the magnitude of toxicity of insecticides to plant growth promoting traits was less severe compared to the higher doses. The sequence of insecticide-toxicity expressed as percent decrease, determined at highest dose rate of each insecticide, over control was: pyriproxyfen (95) = imidacloprid (95) > thiamethoxam (94) > fipronil (85), for phosphate-solubilizing activity while for salicylic acid (SA) it was: thiamethoxam > pyriproxyfen = imidacloprid > fipronil. The impact of the highest dose rate of insecticides on 2,3-dihydroxybenzoic acid (DHBA) was almost equal to those observed for SA. Thiamethoxam decreased the indole acetic acid (IAA) synthesis maximally by 86% whereas fipronil had least toxicity and reduced it by 67% relative to the control. Among the experimental insecticides, pyriproxyfen at 3900 μg l −1 in general, had the greatest toxic effects for plant growth promoting activities of the test strain. The study inferred that insecticides affect the plant beneficial activities of rhizobacteria adversely. These findings are likely to add a new insight into the pest management practices.

Toxicological Effects of Selective Herbicides on Plant Growth Promoting Activities of Phosphate Solubilizing Klebsiella sp. Strain PS19

This study examines the effect of four herbicides, quizalafop-p-ethyl, clodinafop, metribuzin and glyphosate, on plant growth promoting activities like phosphate solubilization, siderophores, indole acetic acid, exo-polysaccharides, hydrogen cyanide and ammonia production by herbicide tolerant Klebsiella sp. strain PS19. The strain was isolated from mustard rhizosphere. The selected herbicides were applied two to three times at the recommended rates. Klebsiella sp. strain PS19 tolerated a concentration of 1600 μg/ml each of quizalafop-p-ethyl and clodinafop, and 3200 and 2800 μg/ml of metribuzin and glyphosate, respectively. The activities of Klebsiella sp. strain PS19 observed under in vitro environment were persistent in the presence of all herbicides at lower rates. The plant growth promoting activities even-though decreased regularly, but was not lost completely, as the concentration of each herbicide was increased from the recommended to three times of higher doses. Among all herbicides, quizalafop-p-ethyl, generally, showed maximum toxicity to plant growth promoting activities of Klebsiella sp. strain PS19. As an example, 40, 80 and 120 μg/l of quizalafop-p-ethyl added to liquid culture Pikovskaya medium, decreased phosphate solubilizing activity of strain PS19 by 93, 95 and 97%, respectively over untreated control. The study revealed that the higher rates of herbicides though decreased the plant growth promoting activity but it did not completely inhibit the metabolic activities of strain PS19. The herbicide tolerance together with growth promoting activities observed under herbicide stress suggests that Klebsiella sp. strain PS19 could be used as bacterial preparation for facilitating the growth and yields of crops even in soils polluted with herbicides.

Plant growth promoting activities of phosphate-solubilizing Enterobacter asburiae as influenced by fungicides

Four fungicides, tebuconazole, hexaconazole, metalaxyl and kitazin were applied at recommended and higher rates to examine their effects on the plant growth promoting activities of the fungicide tolerant Enterobacter asburiae strain PS2 under in vitro conditions. Enterobacter asburiae strain PS2 was isolated from the mustard rhizosphere and was assessed for the fungicide-tolerance and production of plant growth promoting traits (phosphate solubilization, siderophores, indole acetic acid, exo-polysaccharides, hydrogen cyanide and ammonia production) both in the presence and absence of fungicides. Enterobacter asburiae strain PS2 showed plant growth promoting activities even in the presence of fungicides which however, decreased progressively with the increase in fungicide concentration. Fungicides at recommended dose had little effect while the dose higher than the recommended one adversely affected the physiological traits, like, phosphate solubilization, siderophore, and indole acetic acid synthesis. Among all fungicides, tebuconazole in general, showed maximum toxicity to plant growth promoting activities. Fungicide-tolerant E. asburiae strain PS2 with the inherent ability to produce growth regulators even in the presence of fungicides can be exploited as a bio-inoculant to increase the productivity of crops grown in fungicide stressed soils.

Plant performance, dioxygenase-expressing rhizosphere bacteria, and biodegradation of weathered hydrocarbons in contaminated soil

Two greenhouse pot experiments were conducted to investigate the potential of 13 plant species (grasses, cruciferes, legumes, herbs) to thrive in a long-term contaminated soil from a former manufactured gas plant (MGP) site, to promote the proliferation of total and aromatic ring dioxygenase-expressing bacteria (ARDB) in the root zone, and to foster the biodegradation of petrol hydrocarbons (PHCs) and polycyclic aromatic hydrocarbons (PAHs). PHCs at 23 200 mg kg −1 and PAHs at 2194 mg kg −1 reduced seed germination, plant survival, and shoot yields for most plants. Total bacteria and ARDB were generally more abundant in contaminated soil and were most numerous in the rhizosphere of mustard. During 68 d, the loss of total petrol hydrocarbons (TPHs) and total US EPA priority PAHs (TPAHs) was greatest in soil planted with hemp and mustard. Pea, cress, and pansy increased the amounts of PAHs extracted from soil, including an almost 60% increase for dibenzo( ah)anthracene. Plants may enhance the chemical extractability and perhaps biological availability of initially unextractable molecules.

Distribution of vesicular-arbuscular mycorrhizal fungi in the natural ecosystem

Natural occurrence of vesicular-arbuscular mycorrhizal (VAM) fungi in Haryana soils showed that VAM sporulation was more intensive in the rhizosphere of nonlegumes than of legumes. Maximum number of spores (342 spores per 50 g of soil) was observed in the rhizosphere of mustard, followed by chickpea, wheat, pearl millet and pigeonpea. Four VAM generaviz. Glomus, Gigaspora, Sclerocystis andAcaulospora, were present there. Soil pH, total soil P, available P, type of soil, soil moisture and cropping season all variables influenced the VA mycorrhizal population in the natural ecosystem. Numbers of VAM spores highly correlated with the presence of total soil P and soil pH indirectly affected the VAM population through the total soil P. The spore population was abundant in sandy soils as compared to loamy sands. Drier soils had higher number of VAM spores. In summer, the VAM population in soil was less as compared to winter season.