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Synergistic interactions among root‐associated bacteria, rhizobia and chickpea under stress conditions

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  • National Research University
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Abstract

The abiotic stresses such as drought and salinity are an increasing problem in agricultural soils in many parts of the world, and stress tolerant cropping systems are in great demand. Chickpea is known as sensitive plant and abiotic stresses are responsible for considerable yield loss. The increase of chickpea production by exploiting better colonization of the roots through application of effective plant beneficial bacteria to the seed or to the soil considered as the best agricultural technology. Mixed inoculation with PGPR and Rhizobium creates synergistic interactions that may result in a significant increase in growth, symbiotic performance, and uptake of mineral nutrients such as phosphorus, nitrogen, potassium and increase stress resistance of plants. Thus, co-inoculation of chickpea with rhizobia and PGPR could be a useful approach for improving growth, nodulation and yield by reducing dependence on chemical fertilizers. This paper examines recent studies on the impact of salt and drought stresses on plant growth and symbiotic performance of chickpea; interactions of rhizobia and PGPR in the rhizosphere; the ameliorative and beneficial effects of PGPR on plant growth and yield of chickpea under hostile environment.

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... In Uzbekistan, chickpea is usually grown in the marginal condition where the soil has a high concentration of salinity and widespread N deficiency (Khaitov et al. 2016). The soil mineral N content of these soils is influenced by improper crop rotation, deep fallowing and excessive chemical fertilization (Egamberdieva, Abdiev, and Khaitov 2015). Chickpea has an ability to restore soil fertility due to deep penetrating root system which enables them to utilize the limited available nutrients and moisture (Tripathi et al. 2015), also the symbiotic association with rhizobial strains with the function of the biological N fixation improves soil fertility. ...
... Excessive amount of chemical fertilizers are applied annually in terrestrial agrosystems with an idea to produce more agricultural products (Baligar, Fageria, and He 2001;Malhi et al. 2002), and fertilizer rates used are expected to increase in the future if the same conventional agricultural practices are maintained to increase food production to meet the demand of the increasing world population (Tilman et al. 2002;Cordell, Drangert, and White 2009). A value of indicators of soil fertility such as soil organic matter and available nutrients are getting lower with the intensive application of chemicals (Egamberdieva, Abdiev, and Khaitov 2015). Therefore, it is crucial to optimize the efficiency of chemical fertilizers application in agricultural production (Dutta and Bandyopadhyay 2009;White and Brown 2010). ...
... In this study, Rhizobium inoculation significantly increased seed yield of chickpea compared without inoculation at all rate of N fertilization. There are many studies with beneficial bacteria inoculation reported remarkable yield increases in chickpea (Kantar et al. 2003;Dutta and Bandyopadhyay 2009;Egamberdieva, Abdiev, and Khaitov 2015). ...
Article
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... Inoculation with beneficial microbes increases the absorption of nutrients by plants that are usually adversely affected by salt stress (Yang, Kloepper, and Ryu 2009), hence the synthesis of chlorophyll pigments increases in inoculated plants. Some researchers revealed that plants inoculated with PGPR showed decreased Na þ level (Egamberdieva, Abdiev, and Khaitov 2015). This fact is in agreement with our study that co-inoculation Azotobacter and Rhizobium significantly decreased the uptake of Na þ in plant biomass. ...
... Soil salinity negatively affects soil microorganisms that promote plant growth, such as Burkholderia spp., Pseudomonas spp., arbuscular mycorrhizal fungi and nitrogen-fixing Rhizobium spp. (Egamberdieva, Abdiev, and Khaitov 2015). Thus, soil salinity could change the community compositions of bacteria and fungi, in turn altering soil ecosystem functions and plant health (Dixon and Wheeler 1986). ...
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... Legumes could fix N biologically, but only after they form nodules with Rhizobium. The Rhizobium-legume symbiosis has received most attention as they are widely deployed in agricultural practices for sustainability of crop yield and recovery of soil fertility (Egamberdieva et al. 2015). ...
... We have observed that soil nutrients were increased under chickpea grown in association with Rhizobium strains R4, R6 and R9. It is most probably related to greater release of exudates and availability of N and C substrates, due to legumes extensive rooting system (Egamberdieva et al. 2015), and the availability of mineral nutrients in soil which are of considerable importance to increasing microbial populations . Chickpea had a versatile capacity to produce greater root exudates and enrich the soil with nitrogen through nitrogen-fixing activities (Tripathi et al. 2015). ...
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... There is an expanding body of literature showing that plant secondary metabolites can alter plant microbiomes and result in differential microbial community assembly [26,27]. Plants release a large proportion of their photosynthates through the soil rhizosphere [28,29] which activates nutrient mobilizing symbionts and/or beneficial plant growth-promoting (PGP) bacteria [30,31]. Plant secondary metabolites impact microbiome structure by acting as signaling molecules, nutrients sources, or as direct toxins [27,32]. ...
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... At 70 DAS and at harvest stage higher crop growth rate was observed with the application of B3 which was significantly superior over all other treatments. Application of biofertilizers increases the crop growth rate due to adequate availability of nutrients by solubilisation and mineralization process that attributed to more plant growth and dry matter accumulation at active vegetative stages which ultimately increased the crop growth rate (Egamberdieva et al. 2015). ...
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A field experiment was conducted during Rabi season of 2016-2017 at the SIF Farm of CSAUAT, Kanpur, Uttar Pradesh to evaluate the “Effect of different fertility levels and biofertilizers on productivity and profitability of late sown chickpea [Cicer arietinum L.]”.The experiment comprised of 12 treatment combinations in split plot design which comprised 4 treatments [F1 (control), F2 (RDF 100%), F3 (75% RDF), F4 (50% RDF)] in main plot and 3 treatments [B1 (Rhizobium + PSB), B2 (Rhizobium + PGPR) and B3 (Rhizobium + PSB + PGPR)] in sub plots with three replications. The result showed that among the different fertility levels, application of 100% RDF significantly enhanced the yield attributes over the control treatment. Among the different biofertilizers treatments application of Rhizobium + PSB + PGPR significantly higheryield attributes compared to Rhizobium + PGPR. The combined application of 100% RDF with Rhizobium + PSB + PGPR resulted significantly higher seed yield, gross return, net return and B: C ratio of late sown chickpea during Rabi season.
... This can be attributed to the fact that microbial activity, similar to microbial biomass, is a reliable indicator of the amount of easily decomposable organic carbon and is significantly higher in treatments with higher organic carbon content (Kumar et al., 2003). Similar results were reported by Egamberdieva et al. (2015) that increasing organic carbon content improved microbial enzyme activities. ...
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A field experiment was conducted during Rabi season of 2016-2017 at the SIF Farm of CSAUT, Kanpur, Uttar Pradesh to evaluate the fertility levels and biofertilizers on the chemical and biological properties of soil under late sown chickpea [Cicer arietinum L.]. The experiment comprised of 12 treatments combination and laid out in split plot design 4 RDFs control, RDF 100%, 75% RDF and 50% Recommended dose of fertilizer with assigned in main plot. Each main plot further divided into 3 sub plot accommodate three levels of biofertilizers Rhizobium + PSB, Rhizobium + PGPR and Rhizobium + PSB + PGPR and replicated thrice. The result showed that among the different fertility levels, application of 100% RDF were recorded significantly better chemical properties, microbial populations and enzymatic activity after harvest of chick pea crop. Among the biofertilizer treatments, application of Rhizobium + PSB + PGPR were resulted significantly better chemical properties, microbial populations and enzymatic activity followed by 75% RDF after harvest of chick pea crop under late sown condition.
... Whenever, highest number of nodules were recorded with the application of Rhizobium + PGPR which was statistically at par with Rhizobium + PSB + PGPR but significantly higher than Rhizobium + PSB and Rhizobium + PSB. This might be due to nutrient levels had favourable effect on plant growth over control treatment that results better nutrient availability and increased number of metabolic processes taking place in the plant body, which results more root dry weight, number of nodules and nodule dry weight (Egamberdieva et al., 2015). ...
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A field experiment was conducted during rabi season of 2016-2017 at the Students' Instructional Farm of Chandra Shekhar Azad University of Agriculture and Technology, Kanpur, Uttar Pradesh to assess the “impact of fertility levels and biofertilizers on root architecture, yield and nutrient uptake by crop”. The experiment was comprised of 12 treatment combination in split plot design with three replications. The results showed that, application of 100% RDF significantly enhanced root parameters, yield and nutrient uptake over control plot. Among the different biofertilizers treatments, application of Rhizobium + PSB + PGPR had significant effect on root parameters and enhanced yield and nutrient uptake as compared to Rhizobium + PGPR. The combined application of 100% RDF with Rhizobium + PSB + PGPR resulted significantly higher yield of chickpea during rabi season.
... Plants deposit approximately 11% of fixed carbon into the rhizosphere [7,8]. The released carbon may appear to represent a significant energy loss for the plant; however, it may actually be beneficial due to the stimulation of biological activity in the rhizosphere [9], including stimulation of rhizosphere bacteria [10], which provide the plant with increased nutrient solubility, fixed nitrogen, and/or competitive suppression of pathogens [11], as well as plant growth promoting molecules [12,13]. Exuded compounds can further change the properties of the surrounding soil and are important for obtaining nutrients, mediating biological interactions, or decreasing the toxicity of pollutants [14,15]. ...
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Secondary plant metabolites (SPMEs) play an important role in plant survival in the environment and serve to establish ecological relationships between plants and other organisms. Communication between plants and microorganisms via SPMEs contained in root exudates or derived from litter decomposition is an example of this phenomenon. In this review, the general aspects of rhizodeposition together with the significance of terpenes and phenolic compounds are discussed in detail. We focus specifically on the effect of SPMEs on microbial community structure and metabolic activity in environments contaminated by polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs). Furthermore, a section is devoted to a complex effect of plants and/or their metabolites contained in litter on bioremediation of contaminated sites. New insights are introduced from a study evaluating the effects of SPMEs derived during decomposition of grapefruit peel, lemon peel, and pears on bacterial communities and their ability to degrade PCBs in a long-term contaminated soil. The presented review supports the "secondary compound hypothesis" and demonstrates the potential of SPMEs for increasing the effectiveness of bioremediation processes.
... 84, Müncheberg 15374, Germany e-mail: egamberdieva@yahoo.com 2015) that are along responsible for the loss of at least 10 % of global food production (Triky-Dotan et al. 2005;Egamberdieva et al. 2016). Limiting crop losses due to salinity, drought, and diseases is a major area of concern to cope with the background of increasing food requirements (Parvaiz and Satyawati 2008;Shanker and Venkateswarlu 2011). ...
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Soil salinity is one of the main abiotic stresses, which restrict the plant growth and development, and therefore causes major threat to crop productivity. To minimize the crop loss, plant biologists are searching alternatives to develop salt-tolerant crop plants through different means such as plant breeding and genetic engineering. These approaches are successful and presently under use in developed countries but are too costly for the developing countries. In the present scenarios, various methods are utilized all over the globe to mitigate the adverse effect of salinity. One of the commonly used methods is to use beneficial bacteria and fungi that colonize with the plant roots and ultimately alleviate the salinity stress in plants. Among them, application of arbuscular mycorrhizal (AM) fungi has been found to be very effective in mitigating the salinity stress and also improves the crop yield. Various parameters were thoroughly studied and reported in the literature and have demonstrated positive effect in plants subjected to AM fungi under different environmental stress including saline stress. This is attributed to increased antioxidative activities, osmolytes and osmoprotectants in tolerant plants. Deficiency of mineral content in plants under salt stress is compensated by the use of AM fungi as the hyphae of AM fungi acquire minerals in abundance and thereby prevent the plants against deleterious effects of salinity stress. Efficient use of AM fungi can bring the wonders in the field of agriculture with improved yield of crop under salt stress and soil health. Besides this, identification of novel genes that regulate and maintain the biosynthesis of proline and water status in plant cells will help plant researchers to utilize this beneficial interaction in more sustainable ways. The chapter will throw light on the use of AM fungal association in alleviating salt stress in plants and how to exploit this for improved productivity under growth-limited conditions.
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Among the environmental stresses, drought stress is one of the important factors that influence on the yield, yield components and physiological characteristic of the crops under rain-fed conditions. As regards, in the Iran the most cropping area of the chickpea is rain-fed, so, using of the biological agents with once performance supplemental irrigation during growth can be effective in improving the nutritional status of the chickpea. So that, a field experiment was conducted as split-factorial based on Randomized Complete Block Design with three replications, at the Experimental Farm at Campus of Agriculture and Natural Resources of Razi University, in 2010-2011. The main plots consisted of the supplemental irrigation at time of the flowering and non-irrigation and sub-plots were including use and non-use of the Mycorrhiza, Rhizobium and humic acid as factorial. Traits including relative water content (RWC), biological yield, grain yield, number of pods per plant, number of grains per plant, number of grains per pod, 100-grains weight and harvest index. The results showed that the main effect of the supplemental irrigation on yield, yield components (except 100-grains weight), RWC, N and P content were significant. Also, the effect of the humic acid was significant on RWC, biological yield, grain yield, harvest index and P content but the Rhizobium wasn't effective on the traits. The Mycorrhiza only was significant for grain yield and P content. Also the interaction effects between supplemental irrigation and humic acid were significant for biological yield and grain yield and P content. Overall, application of the supplemental irrigation with use of biological and symbiosis agents was effective in improving physiological traits.
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Vermicomposting is a non-thermophilic, boioxidative process that involves earthworms and associated microbes. This biological organic waste decomposition process yields the biofertilizer namely the vermicompost. Vermicompost is a finely divided, peat like material with high porosity, good aeration, drainage, water holding capacity, microbial activity, excellent nutrient status and buffering capacity thereby resulting the required physiochemical characters congenial for soil fertility and plant growth. Vermicompost enhances soil biodiversity by promoting the beneficial microbes which inturn enhances plant growth directly by production of plant growth-regulating hormones and enzymes and indirectly by controlling plant pathogens, nematodes and other pests, thereby enhancing plant health and minimizing the yield loss. Due to its innate biological, biochemical and physiochemical properties, vermicompost may be used to promote sustainable agriculture and also for the safe management of agricultural, industrial, domestic and hospital wastes which may otherwise pose serious threat to life and environment.
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Four cultivars of chickpea, two of them of Mediterranean origin (kabuli), CSG 9651, BG 267 and two Indian (desi) types, CSG 8962, DCP 92-3, differing in their salt sensitivities were identified after screening ten genotypes in saline soils. The cultivars CSG 9651 and CSG 8962 were salt tolerant while BG 267 and DCP 92-3 were salt sensitive, respectively. The seeds of different cultivars were inoculated with Mesorhizobium ciceri, strain F: 75 and the plants were grown in the greenhouse. After the establishment of symbiosis, 15-day-old seedlings were administered doses of saline at varying concentrations (0, 4, 6, 8 dSm-1 NaCl, Na2SO4, CaCl2). Plants were harvested at 40, 70 and 100 days after sowing, for analyses. The main aim was to compare the relative salt tolerance of both desi and kabuli cultivars in terms of nitrogen fixation and carbon metabolism, as well as to ascertain whether the negative effects of saline stress on nitrogen fixation were due to a limitation of photosynthate supply to the nodule or to a limitation on the nodular metabolism that sustains nitrogenase activity. Plant growth, nodulation and nitrogenase activity was more severely affected in BG 267 and DCP 92-3 under salinity treatments (6 and 8 dSm-1) compared with CSG 9651 and CSG 8962. Nodule number as well as nodule mass increased under salt stress in CSG 9651 and CSG 8962 which might be responsible for their higher nitrogen fixation. Salinity reduced leaf chlorophyll and Rubisco activities in all cultivars. However, tolerant cultivars CSG 9651 and CSG 8962 showed smaller declines than the sensitive ones. Phosphoenolpyruvate carboxylase (PEPCase) activity increased significantly in the nodules of tolerant cultivars under salt stress at all harvests, and this was clearly related to salt concentrations. Our results suggest that in salt-affected soils tolerant cultivars have more efficient nodulation and support higher rates of symbiotic nitrogen fixation than the sensitive cultivars.
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The effect of salinity on growth response, nitrogen (N) fixation and tissue mineral content was investigated for four legumes: faba bean (Vicia faba L), pea (Pisum sativum L), soybean (Glycine max L), and common bean (Phaseolus vulgaris L). Plants were grown in a vermiculite culture system supplied with a N‐free nutrient solution with the addition of 0, 50, and 100 mM NaCl. Plants were harvested at the beginning of the flowering period and the dry weights of shoots and roots and acetylene reduction activity (ARA) were evaluated at the same time plant tissues were analysed for N, potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) contents.The depressive effect of saline stress on ARA of nodules was directely related to the salt induced decline in dry weight and N content in shoots. Growth inhibition by NaCl treatments was greater for the pea than for other legumes, whereas the soybean was the most salt‐tolerant Saline stress also affected the N content in shoots and roots. In general the N content accumulated in the shoot and Na in the roots of the four legumes tested, while K accumulated both organs. The acquisition of other macronutrients differed according to the legume species. The legumes most sensitive were P. sativum and V. faba which accumulated Ca in shoot and Mg both in the shoot and the roots. On the contrary, in G. max and P. vulgaris, the two most salt tolerant legumes, accumulated Mg in the roots and Ca in both vegetative organs. Our results suggest a relationship between the salt‐tolerant range in legumes and the macronutrient accumulation in vegetative organs.
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In the tropics, improving protein production depends on increasing agricultural productivity while maintaining low production costs. A major factor limiting productivity is nitrogen fertilizer and, in this context, grain legumes are a foremost alternative because of their high protein content and ability to obtain fixed nitrogen via biological fixation. Nitrogen fixation in the legume/Rhizobium symbiotic system is the result of a complex integration of physiological functions between the host plant and the endophyte. It depends on an exchange of specific metabolities: the bacteroids have an obligatory requirement for carbon substrates as their source of energy and carbon skeletons for nitrogen fixation and assimilation, and the plant receives the nitrogenous products exported from nodules which are required for protein synthesis. Maximizing biological nitrogen fixation to provide nitrogen for high and reliable yields of grain legumes clearly requires an understanding of the functioning of the symbiotic system, the integrated carbon and nitrogen economies, the processes limiting nodule activity and efficiency, as well as the environmental factors potentially detrimental to the plant/bacteria association.
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Collar rot of chickpea (Cicer arietinum) is caused by the soil-borne pathogen Sclerotium rolfsii and management of this ubiquitous pathogen is not possible through a single approach. An integrated approach was adopted by using vermicompost and an antagonistic strain of Pseudomonas syringae (PUR46) possessing plant growth-promoting characteristics. Treatments with vermicompost (10%, 25%, and 50% v/v) and PUR46 alone and in combination reduced seedling mortality in chickpea under glasshouse conditions. The combined effect of 25% vermicompost substitution along with seed bacterization with PUR46 was the most effective treatment, which not only increased the availability and uptake of minerals like P, Mn, and Fe in chickpea seedlings, resulting in an increase in plant growth, but also reduced plant mortality. These effects are correlated with improvement in soil physical conditions and enhanced nutritional factors due to vermicompost substitution as well as plant growth promotion and the antagonistic activity of PUR46 against the pathogen. Dual cultures of PUR46 with the S. rolfsii isolate revealed a high degree of antagonism by PUR46 against the pathogen. Performance of PUR46 was enhanced in the presence of 25% vermicompost compared with its application alone and therefore this combination may be a useful tool to manage S. rolfsii under field conditions.
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Rhizobia inoculated onto legume seeds are often exposed to adverse environmental conditions, which can affect survival and subsequent effectiveness. Hence, soil-applied granular inoculants have received much attention recently. We examined the efficacy of various inoculation methods at four sites in Saskatchewan, Canada, in 1997 and 1998 using desi- and kabuli-type chickpea (Cicer arietinum L.). Seed inoculation treatments (liquid or peat-based powder) were compared with soil inoculation (granular inoculant) either placed in the seed furrow or side-banded (i.e., 2.5 cm to the side) at depths of either 2.5 or 8 cm below the seed. Nodule formation in the seed inoculation treatments was restricted to the crown region of the root system, whereas soil inoculation enhanced nodulation on the lateral roots. In 1997, granular inoculant placed below the seed increased kabuli seed yield by 36 and 14% over the liquid and peat-based inoculants, respectively, whereas desi seed yield increased 17 and 5%, respectively. Seed yield responses were inconsistent in 1998. Seed protein concentration, percentage N derived from the atmosphere (%Ndfa), and amount of N2 fixed were typically lower for the liquid inoculant than for the peat and granular inoculants, which did not differ. The dry weight of lateral-root nodules was highly correlated with yield parameters, suggesting that the lateral-root nodules contributed significantly to N2 fixation and yield. Although the peat and granular inoculants were equally effective in establishing successful symbiosis, placing granular inoculant 2.5 to 8.0 cm below the seed may improve yield and quality.
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Numerous studies have shown that soil salinity decreases nodulation and dramatically reduces N2 fixation and nitrogenase activity of nodulated legumes. Thus, the development of salt-tolerant symbioses is an absolute necessity to enable cultivation of leguminous crops in salt-affected soils. Dual inoculation of legumes with plant growth promoting rhizobacteria (PGPR) and rhizobia has been reported to increase the number of nodules compared to those formed by a rhizobial strain alone. The production of IAA by Pseudomonas strains represents a beneficial mechanism that promoted enlargement of root system, and thereby further enhanced nutrient uptake, nodulation and shoot growth of leguminous plants. When PGPR are able to alleviate salt stress experienced by the plant, more nodules might develop into nitrogen-fixing ones, thereby enabling the plant to obtain part of its nitrogen from the atmosphere. Co-inoculation techniques could be a new approach to increase the salt tolerance and yield of legumes used for the food and green manure production in salt-affected soils, providing supply of biologically fixed N at low cost.
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High salinity of soils in arid and semi arid regions results in desertification and decreased crop yield. In such conditions plants become more vulnerable to diseases caused by pathogenic fungi. The aim of the present work was to select enhanced root colonizing bacteria for their ability to promote plant growth and control root rot of cotton caused by Fusarium oxysporum in salinated soil. The best five enhanced cotton root tip colonizer bacteria were selected from the rhizosphere of cotton grown in saline soil and were identified by the 16S rRNA gene sequence as Pseudomonas spp., Pseudomonas putida, P. chlororaphis, Pseudomonas mendocina and Pantoea agglomerans. They showed ability to promote plant growth and to control root rot of cotton caused by F. oxysporum. Infestation of the soil with F. oxysporum resulted in an increase of diseased plants up to 60%. Selected bacterial strains, reduced this proportion to as low as 19 % and also stimulated cotton growth. These results are promising for the application of selected environmentally safe biological control agents in protecting cotton against root rot disease in saline agricultural soils.
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Abstract The aim of the present study was to isolate plant-beneficial bacteria (both Rhizobium and plant growth promoting rhizobacteria) from roots and nodules of chickpea (Cicer arietinum L.) and to study the effect of coinoculations on growth of two cultivars of chickpea. Four Rhizobium strains were obtained from roots and four from the nodules of field-grown chickpea cv. Parbat and identified on the basis of morphological characteristics, and biochemical and infectivity tests on the host seedlings. Only one type of nitrogen and carbon source utilisation pattern and DNA banding pattern of random amplified polymorphic DNA was observed in all isolates (Rn1, Rn2, Rn3, Rn4) from nodules, while two types of such patterns were detected among the isolates from roots. The isolate Rr1 from roots also exhibited a pattern identical to those of the isolates from nodules, whereas the remaining three isolates (Rr2, Rr3 and Rr4) from roots showed a different pattern. Two strains of plant growth-promoting rhizobacteria belonging to genus Enterobacter were also isolated from chickpea roots. All the Rhizobium strains and Enterobacter strains produced the plant growth hormones indole acetic acid and gibberellic acid in the growth medium. Effects of the bacterial isolates as single- or double-strain inocula were studied on two chickpea cultivars (NIFA 88 and Parbat) grown in sterilised soil. In cultivar NIFA 88, coinoculation of Rhizobium strain Rn1 with Enterobacter strain B resulted in maximum increase in plant biomass and nodulation, as compared with the control treatment (non-inoculated as well as inoculated with Rhizobium strain Rn1 only), whereas the combination of Rhizobium Rn1 with Enterobacter A was more efficient in growth promotion of chickpea cv. Parbat. In non-sterilised soil, the same combinations of the Rhizobium strain Rn1 with Enterobacter strains A and B were found to be the most effective inoculants for cvv. Parbat and NIFA 88, respectively. However, some negative effects on plant growth were also noted in cv. Parbat coinoculated with Rhizobium strain Rr2 and Enterobacter strain B.
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Pseudomonas isolates obtained from the rhizosphere of chickpea (Cicer arietinum L.) and green gram (Vigna radiata) were found to produce significant amount of indole acetic acid (IAA) when grown in a LB medium broth supplemented with L-tryptophan. Seed bacterization of chickpea cultivar C235 with different Pseudomonas isolates showed stunting effect on the development of root and shoot at 5 and 10 days of seedling growth except the strains MPS79 and MPS90 that showed stimulation of root growth, and strains MPS104 and MRS13 that showed shoot growth stimulation at 10 days. Exogenous treatment of seeds with IAA at 0.5 and 1.0 μM concentration caused similar stunting effects on root and shoot growth compared to untreated control both at 5 and 10 days of observation, whereas higher concentration of IAA (10.0 μM) inhibited the growth of seedlings. Coinoculation of chickpea with IAA-producing Pseudomonas strains increased nodule number and nodule biomass by Mesorhizobium sp. Cicer strain Ca181. The plant dry weights of coinoculated treatments showed 1.10 to 1.28 times increase in comparison to Mesorhizobium-inoculated plants alone and 3.62 to 4.50 times over uninoculated controls at 100 days of plant growth. The results indicated the potential usefulness of allelopathic rhizosphere bacteria and growth-mediating IAA in enhancement of nodulation and stimulation of plant growth in chickpea.
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Background and Aims Salt stress is an increasing problem in agricultural soils in many parts of the world, and salt tolerant cropping systems are in great demand. We investigated the effect of co-inoculation of G. officinalis with Rhizobium galegae and two plant growth promoting Pseudomonas species on plant growth, nodulation and N content under salt stress. Methods The effect of inoculation with R. galegae HAMBI 1141 alone and in combination with the root colonizing P. trivialis TSAU20 or P. extremorientalis 3Re27 on the growth of G. officinalis exposed to salt stress (50 and 75 mM NaCl) was studied under gnotobiotic and greenhouse conditions. Results The growth of goat’s rue was reduced at 50 and 75 mM, NaCl both in gnotobiotic sand system and in potting soil in greenhouse. Co-inoculation of unstressed and salt-stressed goat’s rue either with R. galegae HAMBI 1141 and P. trivialis 3Re27 or P. extremorientalis TSAU20 significantly improved root, shoot growth and nodulation of plant roots grown in gnotobiotic sand system and low-fertilized potting soils compared to that of plants inoculated with R. galegae alone. The nitrogen content of co-inoculated plant roots was significantly increased at 75 NaCl in potting soil Co-inoculation of G. officinalis with either of the two PGPR Pseudomonas strains also improved root tip-colonization by R. galegae cells. Conclusion Thus, the co-inoculation of goat’s rue with Rhizobium and PGPR Pseudomonas strains was able to alleviate salt stress of plants grown in salt-affected gnotobiotic sand system and in potting soil in the greenhouse. Key words: goat's rue, Galega officinalis, Galega orientalis, Rhizobium galegae, Pseudomonas, plant growth promotion, salt stress, bacterial colonization
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The performance of plants (grown in pots) was studied for drought induced at critical stages of grain filling. Furthermore, the effect of abscisic acid (ABA) and benzyladenine (BA), were also studied on the physiology of plants during grain filling. Seeds of two wheat varieties cv Margalla-99 (cv1) and cv Manthar-2003 (cv2) were sown in pots. Stress treatments were imposed immediately after anthesis. Drought stress resulted in maximum decrease in IAA and GA content but proline and ABA content of leaves showed maximum increase at hard dough stage in cv1. With decrease in soil moisture content under induced drought stress, the percentage decrease in IAA and GA and increase in proline and ABA was greater in leaves and spikes of potted plants. All parameters showed greater decrease in cv2 than in cv1. Application of both ABA and BA, each at 10-6 M applied at anthesis stage, was involved in osmoregulation by the production of proline. The adverse effect of drought started at anthesis stage reaching maximum at hard dough stage. ABA was more effective at the later stages of grain filling whereas, BA was more effective at early stages.
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Plant growth promoting rhizobacteria (PGPR) containing ACC-deaminase in combination with rhizobia can improve the growth and nodulation in plants by suppressing the endogenous level of ethylene. In the present study, ten strains, each of PGPR and rhizobia from the previously screened cultures were tested for their effect as coinoculants on growth and nodulation of lentil in growth pouches under axenic conditions. Results showed that most of the combinations improved the lentil growth as compared to the un-inoculated control. Maximum increase in shoot length (1.87 fold), root length (1.97 fold) and total biomass (1.98 fold) over the un-inoculated control was observed in the treatment where the lentil seedlings were inoculated with the combination Z24P10. Co-inoculation also improved the nodulation in lentil and the maximum number of nodules plant-1 (24 nodules) were observed in the combination Z22P10. However, there was no nodulation in few combinations. It is concluded that the coinoculation with rhizobia and PGPR containing ACC-deaminase has improved the growth and nodulation in lentil under axenic conditions and the selected combinations may be evaluated in pot and field trials.
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The effect of co-inoculation with plant growth-promoting rhizobacteria (PGPR) and Rhizobium, on yield and yield components of common bean (Phaseolus vulgaris L.) cultivars was investigated in two consecutive years under field condition. PGPR strains Pseudomonas fluorescens P-93 and Azospirillum lipoferum S-21 as well as two highly effective Rhizobium strains were used in this study. Common bean seeds of three cultivars were inoculated with Rhizobium singly or in a combination with PGPR to evaluate their effect on growth characters. A significant variation of plant growth in response to inoculation with Rhizobium strains was observed. Treatment with PGPR significantly increased pod per plant, number of seeds per pod, weight of 100 seed, weight of seeds per plant, weight of pods per plant, total dry matter in seed filling stage as well as seed yield and protein content. Co-inoculation with Rhizobium and PGPR demonstrated a significant increase in the yield and yield components.
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The involvement of mechanisms other than competition for iron in biological control of Fusarium oxysporum f. sp. dianthi of carnation by Pseudomonas sp. strain WCS417r was investigated. Pathogen and antagonist were spatially separated by bacterizing the roots while inoculating the stem with the pathogen. When the roots were bacterized with strain WCS417r 1 wk prior to stem inoculation with F. o. dianthi, the number of diseased plants in all experiments with cultivar Pallas was reduced from about 50 to 20%, and in one experiment with cultivar Lena from 69 to 38%. Strain WCS417r could not be isolated from stem tissue and control of Fusarium wilt by strain WCS417r, therefore, is not due to competition between F. o. dianthi and strain WCS417r, but has to be ascribed to induced resistance. Along with induced resistance, there was an increased accumulation of phytoalexins in stems of bacterized and inoculated plants compared with nonbacterized, fungus-infected plants. No accumulation of these compounds was found when the plants were bacterized but were noninfected. We concluded that signals, provided by strain WCS417r at the root system, induce in the stem sensitization of defense responses against F. o. dianthi, such as synthesis and accumulation of phytoalexins.
Chapter
This review explores bacterial density-dependent signaling in the rhizosphere and the extent to which it may act as a control point in nitrogen and carbon cycling. Group behavior is a common strategy found throughout nature, and many bacterial species are known to regulate population-level behaviors through extracellular signaling in a mechanism known as quorum sensing (QS). Rhizosphere soil is characterized by increased cell density, increased N-acyl-homoserine lactone (AHL) abundance and QS-controlled behaviors. Microbial enzyme activities that depolymerize macromolecular organic N are likely the rate-limiting steps in N mineralization in the rhizosphere, and in vitro many bacterial species regulate extracellular enzyme production such as chitinase and protease using QS. Despite the abundance of N in the soil, temperate terrestrial plants are generally N limited; up to half of total soil N exists as plant-inaccessible macromolecular organic N, mainly as chitin, proteins, peptidoglycans, and nucleic acids. Soil microbes are generally carbon (C) limited, and rhizosphere carbon deposition fuels heterotrophic cycling of organic N in soil and creates an environment primed for microbial C storage to gain competitive advantage. Changes in a subset of the microbial community, which accompany increases in cell density and activity in the rhizosphere, have been observed, as determined by the 16S rDNA community profile analyses. While proteobacteria likely play a significant role in AHL-mediated QS control of N cycling in soils, there is also a diversity of taxa capable of exoenzyme activity in the rhizosphere that are potentially also functioning in a density-dependent manner. In addition to diffusion sensing, QS may play a role in the rapid response of bacterial populations to the infusion of nutrients provided by an incoming root, which could be a mechanism by which r strategists quickly change gene expression and growth rates in response to such ephemeral resources. Taken together, these data support a role for bacterial QS in rhizosphere microbial growth and survival, which is integral to carbon and nitrogen cycling, and suggest that this behavior may extend beyond the proteobacteria and N cycling as we learn more about microbial diversity and ecology of rhizosphere soils.
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In this paper we review the influence of various soil factors on the legume–Rhizobium symbiotic relationship. Abiotic factors such as extremes in soil pH (highly acidic or alkaline soils), salinity, tillage, high soil temperature and chemical residues, all of which can occur in crop and pasture systems in southern Australia, generally reduce populations of Rhizobium in the soil. Naturally occurring Rhizobium populations, although often found in high numbers, are generally poor in their ability to fix nitrogen and can compete strongly with introduced Rhizobium inoculant. The introduction of new legume genera as a continuing and essential part of change in farming systems usually requires the need to identify new and specific inoculant Rhizobium strains not found in the soil, but necessary for optimum nitrogen fixation. It is therefore necessary to characterise the specific requirements or limitations in the soil for establishing Rhizobium populations to ensure optimal nitrogen fixation following inoculation of legumes. The ability of the introduced Rhizobium to form effective nodules is rarely linked to a single soil attribute; therefore the study of rhizobial ecology requires an understanding of many soil and environmental factors. This paper reviews current knowledge of the influence of soil factors on rhizobial survival, the nodulation process, and nitrogen fixation by legumes.
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The study was undertaken with the aim of testing the effects of isolated bacterial strain nbri05 from arsenic contaminated site of West Bengal. Firstly, isolated strain was characterized by morphological, biochemical and functional characterization and was able to grow at higher concentration of arsenic ranging up to 50,000 mg l−1 of As(V) (arsenate) and 1500 mg l−1 of As(III) (arsenite) concentration. After complete characterization, pot experiment was conducted to scrutinize the role of isolated bacterium nbri05 on arsenic uptake, plant growth, biomass and some biochemical responses of chickpea (Cicer aritenum) were grown in arsenic treated soil amended with 10 mg kg−1 of sodium arsenate. It was observed that nbri05 combat the As toxicity in plants by reducing the As uptake in shoot part and significantly increases plant growth and yield of the chickpea plant in comparison to only arsenic treated plant. Thus, these results clearly show that the bacterium nbri05 owing to its intrinsic abilities of plant growth promotion and accumulates more As in root of the plant may be accounted as a new bacterium for phytostabilization in chickpea.
Article
The rhizosphere as compared to bulk soil is rich in nutrients because of root exudation and deposits. As a consequence, the number of bacteria surrounding plant roots is 10–100 times higher than in bulk soil. These rhizobacteria, based on their effects on plants, can be largely divided into beneficial, deleterious, or neutral bacteria. The beneficial bacteria, also called plant growth-promoting rhizobacteria (PGPR), exert their beneficial effect through either direct or indirect mechanisms or both. In this chapter, the different mechanisms of plant-growth promotion and their impact are discussed. The mechanisms comprise the production of plant growth-promoting substances, nitrogen transformations, increasing bioavailability of phosphate and micronutrients, and biological control, as the best documented cases. In addition, the bacterial production of some molecules with recently described plant growth-promoting effects is discussed. To indicate the impact of PGPR, the applications and relevance of these bacteria in agricultural practices are highlighted. The importance of the plant genotype, inoculum density and technology, and co‐inoculation practices, in terms of plant responsiveness are discussed. It is concluded that basic research should remain a priority in order to be able to develop performing and reliable bacterial inocula as a means to support sustainable agriculture.
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The involvement of mechanisms other than competition for iron in biological control of Fusarium oxysporum f. sp. dianthi of carnation by Pseudomonas sp. strain WCS417r was investigated. Pathogen and antagonist were spatially separated by bacterizing the roots while inoculating the stem with the pathogen. When the roots were bacterized with strain WCS417r 1 wk prior to stem inoculation with F. o. dianthi, the number of diseased plants in all experiments with cultivar Pallas was reduced from about 50 to 20%, and in one experiment with cultivar Lena from 69 to 38% (...)
Article
Two preselected plant growth promoting rhizobacteria (PGPR) containing 1-aminocyclopropane-1-carboxylate (ACC)-deaminase (EC 4.1.99.4) were used to investigate their potential to ameliorate the effects of drought stress on growth, yield, and ripening of pea (Pisum sativum L.). Inoculated and uninoculated (control) seeds of pea cultivar 2000 were sown in pots (four seeds pot−1) and placed in a wire house. The plants were exposed to drought stress at different stages of growth (vegetative, flowering, and pod formation) by skipping the respective irrigation. Results revealed that inoculation of peas with PGPR containing ACC-deaminase significantly decreased the “drought stress imposed effects” on the growth and yield of peas. Exposure of plants to drought stress at vegetative growth stage significantly decreased shoot growth by 41% in the case of uninoculated plants, whereas, by only 18% in the case of inoculated plants compared to nonstressed uninoculated control.Grain yield was decreased when plants were exposed to drought stress at the flowering and pod formation stage, but inoculation resulted in better grain yield (up to 62% and 40% higher, respectively) than the respective uninoculated nonstressed control. Ripening of pods was also delayed in plants inoculated with PGPR, which may imply decreased endogenous ethylene production in inoculated plants. This premise is further supported by the observation that inoculation with PGPR reduced the intensity of classical “triple” response in etiolated pea seedlings, caused by externally applied ACC. It is very probable that the drought stress induced inhibitory effects of ethylene could be partially or completely eliminated by inoculation with PGPR containing ACC-deaminase.
Article
Chickpeas inoculated with two local isolates of Bradyrhizobium, either singly or as a mixed culture, and with an imported strain were compared with an uninoculated treatment in a greenhouse trial using five cultivars of chickpea growing in soil that had not supported legume growth in the recent past. Inoculation gave significant increases in nodule number, nodule dry weight, N accumulation and seed yield with significant strain × cultivar interactions. Although the mixed inoculant was superior in early nodule formation, the local isolates performed better in later measurements. Two recently-developed γ-ray induced mutants of chickpea, G-299 and G-296, nodulated better than the other three cultivars. The data support the use of local bradyrhizobia to prepare inoculant for chickpea and suggest that mutant chickpea genotypes offer potential benefits in N2 fixation and legume yield.
Article
Salinity causes osmotic stress and negatively impacts plant growth and productivity. Proline is one of the most important osmoprotectants synthesized under stressed conditions. Accumulation of free proline occurs due to enhanced biosynthesis and repressed degradation, and both processes are controlled by feedback regulatory mechanisms. Arbuscular mycorrhizal (AM) fungi are considered to be bioameliorators of salinity stress due to their wideranging presence in contaminated soils and their role in modulation of biochemical processes. Chickpea is considered sensitive to salinity. However, reports on AM-induced osmoprotection through regulation of proline biosynthesis in chickpea genotypes are scant. The present study investigated the influence of AM symbiosis on proline metabolism in two chickpea (Cicer arietinum L.) genotypes (PBG 5 and CSG 9505) under salt stress and correlated the same with sodium (Na+) ion uptake. Salinity reduced plant biomass (roots and shoots), with roots being more negatively affected than shoots. Mycorrhizal colonization with Glomus mosseae was much stronger in PBG-5 and was correlated with reduced Na+ ion uptake and higher growth when compared with CSG-9505 under stressed and unstressed conditions. Mycorrhizal symbiosis with chickpea roots boosted proline biosynthesis by significantly increasing pyrroline-5-carboxylate synthetase (P-5-CS) and glutamate dehydrogenase (GDH) activities with a concomitant decline in proline dehydrogenase (ProDH) activity under salt stress. The enhancement of the activity of these enzymes was higher in PBG-5 than in CSG-9505 and could be directly correlated with the percent mycorrhizalcolonization and Na+ uptake. The study indicated a strong role of AM symbiosis in enhancing stress tolerance in chickpea by significantly modulating proline metabolism and Na+ uptake.
Chapter
Crop cultivation in salinated soils is one of the major challenges in agriculture: salinated areas are increasing world-wide and plants growing under saline or water unbalance stress become more vulnerable to diseases caused by soil-borne pathogens. Biocontrol using salt-tolerant, plant growth promoting rhizobacteria (PGPR) to protect plant roots against high salinity and pathogens offers sustainable solutions for plant protection. Screening strategies for specific PGPRs were presented and assessed. Stenotrophomonas rhizophila is a model for a plant-competent, salt-tolerant PGPR. For example, strain S. rhizophila DSM 14405T showed biocontrol activity on various crops under salinated conditions in Uzbekistan. Besides rhizosphere competence and antagonistic activity, the strain DSM 14405T is characterized by the production of high amounts of osmoprotective substances. New insights into the mode of action are presented from genomic information.
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The ability of plants to tolerate salts is determined by multiple biochemical pathways that facilitate retention and/or acquisition of water, protect chloroplast functions and maintain ion homeostasis. Essential pathways include those that lead to synthesis of osmotically active metabolites, specific proteins and certain free radical enzymes to control ion and water flux and support scavenging of oxygen radicals. No well-defined indicators are available to facilitate the improvement in salinity tolerance of agricultural crops through breeding. If the crop shows distinctive indica- tors of salt tolerance at the whole plant, tissue or cellular level, selection is the most convenient and practical me- thod. There is therefore a need to determine the underlying biochemical mechanisms of salinity tolerance so as to provide plant breeders with appropriate indicators. In this review, the possibility of using these biochemical charac- teristics as selection criteria for salt tolerance is discussed.
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Crop cultivation in saline soils is one of the major agricultural challenges world-wide. Cotton production in Uzbekistan is limited by soil salinization and disease caused by soil borne pathogens. The use of plant growth promoting rhizobacteria (PGPR) to control plant diseases and stimulation of plant growth has been considered a viable alternative and environmentally friendly method. The strain P. putida BIST and B. subtilis SUBTIN significantly (p<0.05) increased the total N, P, and K contents of shoot and root (13-27%), plant height (15%), and yield (16%) of cotton in small plot experiments. They were able to produce phytohormone indole-acetic-acid (IAA) under saline conditions and were positive for ACC deaminase activity. On the basis of results, it may be concluded that plant growth promoting rhizobacteria are potential option for improvement of cotton growth and development in salinated arid soil.
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Introduction In grassland farming relatively large amounts of chemical fertilizers applied. It is clear that the situation could be largely improved when the use of chemicals would be replaced by environmentally friendly biologicals together with leguminous plants (Lugtenberg et al., 2004). Legumes such pea can supply not only a good source of protein for livestock, but can also provide a cheap source of nitrogen to support grass production, improve soil organic matter through decaying nodules (Lascano, 2001). The objectives of this work was to monitor the effect of inoculation of soybean and peas with Rhizobium and nitrogen fixing bacterial strains, so as to find and develop the most effective bacterial fertilizers for growing peas under nutrient deficient salinated soil of Uzbekistan. Material and methods Experiments were carried out in arable fields of Tashkent province, north-eastern part of Uzbekistan, characterised by a calcareous serozem soil (1 % organic matter; 0.6 mg N 100 g-1 soil; 3.0 mg P 100 g –1; 12 mg K 100 g–1; 6 mg Mg 100 g–1 soil; pH 7.4). Pea (Pisum sativium) seeds and bacterial strains Pseudomonas alcaligenes 15, and Rhizobium meliloti 39 were used for this study. The bacteria were formulated with peat and seeds were inoculated with bacterial inoculants. Plants were grown in open field conditions with a temperature of 36°C to 38°C during the day and 20°C to 24°C at night. Five weeks after germination, shoots and roots were separated and dried at 105°C before determining the root and shoot dry weight and N, P, K content of plant. The data were analysed with an ANOVA and Student-Newman-Keuls test for testing the significant differences (p<0.05) of main effects. Results The results showed that bacterial inoculants Pseudomonas alcaligenes 15, and Rhizobium meliloti 39 increased shoot and root dry matter of pea significantly from 28 to 38% as compared to the control. Shoot growth increased more than root growth. This increase in biomass translated into significantly higher N, P, and K contents (Table 1). They increased N up to K and P uptake significantly. The bacterial strains were capable of fixing atmospheric N, and were able produce auxin.Conclusion The results obtained in our work can have potential applications of bacterial inoculants as bio fertiliser for increasing the productivity of peas as forage crops under N poor soil conditions of Uzbekistan. References Lugtenberg, B.J.J. and G.V. Bloemberg (2004). Life in the rhizosphere. In: Pseudomonas Vol. 1. Ramos, J.L. (ed), Kluwer Academic / Plenum Publishers, New York, pp. 403-430. Lascano, C.E. (2001). Animal production in grass-legume pastures in the tropics. pg. 219-232. In A. Sotomayor-Rios, A. & W.D. Pitman, W.D. (eds.) Tropical Forage Plants: Development and Uses. p. 219-232. CRC Press, Boca Raton, FL, USA, CRC Press.