USE OF PLANT GROWTH PROMOTING BACTERIA AS INOCULATE IN AGRICULTURAL SOIL TO IMPROVE CROP: A REVIEW
This review contains: A brief historical overview of bacterial inoculants research in the wide areas of rhizosphere biotechnology highlighting new bio inoculants has received great attention during nearby past, and right expert knowledge have been developed. Plant growth-promoting bacteria (PGPB) are bacteria that can enhance plant growth and protect plants from disease and abiotic stresses through a wide variety of mechanisms. Several important bacterial characteristics, such as biological nitrogen fixation, phosphate solubilization, ACC deaminase activity, and production of sidero-phores and phytohormones, can be assessed as plant growth promotion (PGP) traits.
Key words Rhizosphere ,PGPB, Bacterial strain ,inoculation, Nitrogen fixation ,phosphate solublisation, siderophore, Acc deaminase, VOCs , phytohormone
The rhizosphere is the soil-plant root interphase and in practice consists of the soil adhering to the root besides the loose soil surrounding it. Plant growth-promoting rhizobacteria (PGPR) are potential agents for the biological control of plant pathogens (Babalola .,et. al 2010).The rhizosphere can be defined as the land field or soil region where processes mediated by microorganisms are specifically influenced the root system this region includes the soil connected to the plant roots and often extends a few millimeters of the root surface, being an important environment for the plant and microorganism interactions that exert beneﬁcial effects on plant development known as plant growth-promoting rhizobacteria (PGPR) ( Gray and Smith, 2005;Souza .,et al 2015) . One of the basic requirements for the good effect of PGPR is their ability to colonize and come in contact to the hosts rhizosphere, rhizoplane, or the root interior (Glick et al., 2007:parry., et al 2016). A formulation containing one or more beneficial bacterial strains (or species) in an easy -to-use and economical carrier material, either organic, inorganic, or synthesized from defined molecules. The inoculant is the means of bacterial transport from the factory to the living plant. The three fundamental and essential characteristics for all inoculants are to: (1) support the growth of the intended microorganisms, (2) support the necessary number of viable microbial cells in good physiological condition for an acceptable period of time (Stephens,2000,Bahsan., et al 2014 ) .Deliver enough microorganisms at the time of inoculation to reach a threshold number of bacteria that is usually required to obtain a plant response, i.e., the inoculant must contain enough viable bacteria after the formulation process (Date ,2001,Bahsan et al 2014)
PGPR-medi-ated plant growth promotion occurs by the changing of the whole microbial community in the rhizosphere niche by producing the various substances (Kloepper and Schroth 1981; Parray .,et al 2016 ). Some inoculants move into the root interior to establish endophytic populations with the power to adjust to the niche and beneﬁts to the host plants (Compant et al.,2005; Kloepper et al.,1999.,Adesemoye.,et al 2013) . Some bacteria increase root surface area, thus giving a greater value of nutrient uptake, and in turn, induce plant productivity.). Plant growth promoting rhizobacteria can affect plant growth by different direct and indirect mechanisms (Glick 1995 .,Kumar et al.,2015). PGPR effect direct growth promotion of plants by fixing atmospheric nitrogen, Solubilizing insoluble phosphates, secreting hormones such as IAA, , and ACC (1-Aminocycloprapane-1- carboxylic acid) deaminase production which helps in regulation of ethylene. (Kumar et al; 2015). Induced systemic resistance (ISR), antibiosis, competition for nutrients, parasitism, production of metabolites (hydrogen cyanide, siderophores) suppressive to deleterious rhizobacteria, are some of the mechanisms that in a indirectl effect the plant growth (kumaret al ;2015).
Brief Historical Background
In modern cultivation process unselective use of fertilizers, particularly the nitrogenous and phosphorus, has led to considerable pollution of soil, air and water. Use of these extravagant chemicals exerts bad effects on soil microorganism, affects the fertility position of soil and also pollutes environment (Yousaf.,et al 2014; Gupta et al; 2015). The application of these fertilizers on a long term basis often leads to reduction in pH and exchangeable bases thus making them unavailable to crops and the productivity of crop declines. To prevent this problem and obtain higher plant yields, farmers have become increasingly dependent on chemical sources of nitrogen and phosphorus, as well as being costly, the production of chemical fertilizers depletes nonrenewable resources, the oil and natural gas used to produce these fertilizers, and these put harmful impact on human and environment (joshi., et al 2006;Gupta et al ;2015) Inoculation of plants with useful bacteria can be outline back for centuries. From experience, farmers knew that when they mixed soil taken from a previous legume crop with soil in which non legumes were to be grown, as result crop yield improve. By the end of the 19th hundred , the experience of mixing “naturally inoculated” soil with seeds became a recommended and careful way of legume inoculation in the USA (Smith, 1992;Bashan ,1998).Latter on in U.S pure culture rhizobia will be used and start the commercialization of artificial inoculation their patent culture placed in market under the name nit Ragin and 1st pure culture of a desire strain of rhizobia grown in a flat glass medium containing only a small amount of gelatin medium this material either to be supplied to the seed or mixed with soil and spread over the field and worked over the 7.6 cm(Nobbeet al ;1986;smith et al.,1992).
MECHANISM OF PLANT GROWTH PROMOTION
Plant growth promoting bacteria effect the growth by the two different method direct and indirect mechanism.
Direct PGPR enhance plant growth in the absence of pathogens. In accordance with soil bacterial species in the plant rhizosphere which grow in, on, or around plant tissues activate plant growth by the large no of mechanisms. In addition to providing the mechanical support and enhancing the water and nutrient uptake, microbial activity in the rhizosphere affects rooting patterns and the supply of available nutrients to plants (Jan et al ;2016). Endophytic bacteria have more advantage over rhizospheric bacteria because they get the opportunity to stay in direct contact with the plant tissues. Also, they offer more beneficial effects to the plants as compared to bacteria residing outside plants. However, rhizospheric colonials have been found to be the major source of endophytic colonization. Some people even consider endophytes as subsets of rhizospheric micro biome (Araujo., 2002 . Chaturvedi et al ;2016).
Nitrogen is generally considered one of the major limiting nutrients in plant growth. The biological process responsible for reduction of molecular nitrogen into ammonia is referred to as nitrogen fixation. A wide diversity of nitrogen-fixing bacterial species belonging to most phyla of the Bacteria domain has the capacity to colonize the rhizosphere and to interact with plants. Leguminous and actinorhizal plants can obtain their nitrogen by association with rhizobia or Frankia via differentiation on their respective host plants of a specialized organ, the root nodule (Bhat et al .,2015). Most instances bacteria colonize only the surface of the roots and remain vulnerable to competition from other rhizosphere micro-organisms, even when the nitrogen-fixing bacteria are endophytic, benefits to the plant may result from better uptake of soil nutrients rather than from endophytic nitrogen fixation (Cocking et al .,2003). The first industrial production of rhizobium inoculant began by the end of the 19th century. However, to sustain production of cereal crops, legumes and other plants of agricultural importance, the supply of nitrogenous chemical fertilizers has been regularly increasing since the Second World War. According to an FAO report, production of N fertilizer for 2007 was 130 million tons of N, and this should further increase in the coming years. Biofertilizers can add 20-200kg N ha (by fixation), liberate growth-promoting substances and increase crop yield 10_50% . (Ghany et al .,2013). They are cheaper, pollution free, based on renewable energy sources and also improve soil.( Two groups of nitrogen fixing bacteria have been studied alot, which includes Rhizobia and Frankia. (Frankia strains are N2-fixing actinomycetes whose isolation and cultivation were first reported in 1978. They induce N2-fixing root nodules on diverse nonleguminous (actinorhizal) plants that are important in ecological successions and in land reclamation and remediation. The genus Frankia encompasses a diverse group of soil actinomycetes that have in common the formation of multilocular sporangia, filamentous growth, and nitrogenase-containing vesicles enveloped in multilaminated lipid envelopes. The relatively constant morphology of vesicles in culture is modified by plant interactions in symbiosis to give a diverse array of vesicles shapes (Benson et al .,1993).
Phosphate solublisation bacteria and their role to improve crop
Biological nitrogen fixation is very important in enhancing the the soil fertility. In addition to biological nitrogen fixation, Maximum crop yields require sufficient phosphorus fertilization. Only phosphate in a soluble ionic form (Pi) is effective as a mineral nutrient ( Goldestien et al ;1986) .Phosphate solubilization is equally important , Phosphorus (P) is major essential macronutrients for biological growth and development.the use of phosphate solubilizing bacteria as inoculants simultaneously increases P uptake by the plant and crop yield. However, direct inoculation of free phosphate solubilizing bacteria (PSB) into soil is not easy to maintain cells survival around plants roots because it is susceptible to a variety of environmental soil variation such as temperature, humidity and salt stress (Wu et al., 2012 . M. Schoebitz et al ;2013 ). Variability of PSB inoculation on plant is mainly due to the quality in the inoculants formulations containing an effective bacterial strain and can determine the success or failure of a biological agent. Therefore, the goal will be to find an adequate formulation to convert a promising bacteria strain into a commercial inoculant product (Bashan, 1998 Schoebitz et al ; 2013 ). Strains from the genera Pseudomonas, Bacillus and Rhizobium are among the most powerful phosphate solubilizers. The basic mechanism for mineral phosphate solubilization is the production of organic acids, and acid phosphatases play a great role in the mineralization of organic phosphorous in soil (Rodríguezet al; 1999). The use of phosphate-solubilizing bacteria (PSB) as inoculants simultaneously increases P uptake by the plant and crop yield. Ectorhizospheric strains from pseudomonads and bacilli, and endosymbiotic bacteria from rhizobia have been described as effective phosphate solubilizers. The production of organic acids is considered as the principal mechanism for mineral phosphate solubilization in bacteria. This assumption has been supported by the cloning of two genes involved in gluconic acid production: PQQ synthase and gabY genes ( Mariano et al ;2001).
Siderophores can be defined as small peptidic molecules containing side chains and functional groups that can provide a high-affinity set of ligands to coordinate ferric ion (Crosa and Walsh, 2002).). Iron is a vital element require by all living organisms for many cellular processes such as electron transport chain and as a cofactor for many enzymes(Litwin et al., 1993 ,Ali et al ;2013) .PGPR secrete siderophores. Siderophores are low molecular weight iron binding protein compounds involved in the process of chelating ferric iron (Fe (iii)) from the environment. When Fe is limited, microbial siderophores provide plants with Fe, enhancing their growth In addition, GrrA/GrrS, but not GacS/GacA, are involved in siderophore synthesis regulation in Serratia plymuthica strain IC1270, suggesting that gene evolution occurred in the siderophore-producing bacteria.(M., X. Liu.,et al 2004:Compant et al; 2015) . The plant growth promotion traits of Pseudomonas aeruginosa, P. fluorescens and Bacillus subtilis isolated from the maize (Zea mays L.) rhizosphere. In vitro studies refelact that isolates have the potential to produce indole acetic acid (IAA), hydrogen cyanide, phosphate solubilisation, and Siderophores are small organic molecules produced by microorganisms under iron-limiting conditions which enhance the uptake of iron to the microorganisms ( Saha M et al; 2016, Karnawal 2017). Siderophore-producing microbial inoculants have direct effect on plant growth ,shown in various crop in the past. Pseudomonas aeruginosa, Pseudomonas fluorescensor Ralstonia metallidurans, able to produce siderophores, were inoculated in an agricultural soil containing Cr (488 mg kg−1) and Pb (382 mg kg−1) and maize was cultivated(Braud et al;2009) .In another experiment, inoculation of Arabidopsis thaliana with Pseudomonas fluorescens resulted in the uptake of the Fe-pyoverdin complex synthesized by the bacteria leading to an increase in the iron level inside the plant tissue and enhanced the plant growth(Vansuyt et al; 2007 ). Microbes produce variety of siderophores and a major class includes catechols and hydroxamate. Numerous strains of actinobacteria have been reported as siderophore producers (Wang et al,. 2014 Sathya et al ;2017)
Bacteria with ACC deaminase help to promote the growth of plant
Plant growth-promoting bacteria that contain the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase pomote plant growth and development by decreasing plant ethylene levels, especially following a variety of environmental stresses (Glick,et al 2007). Certain plant growth promoting rhizobacteria (PGPR) contain a important enzyme, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which regulates ethylene production by metabolizing ACC (an immediate precursor of ethylene biosynthesis in higher plants) into α-ketobutyrate and ammonia. Inoculation with PGPR containing ACC deaminase activity could be helpful in maintain the plant growth and development under stress conditions by reducing stress-induced ethylene production (saleem et al 2007).) . Bacteria that express ACC deaminase can lower the impact on plants of a range of different stresses . For example, both endogenous and exogenous ACC deaminase genes increase the symbiotic performance of many rhizobial strains (Ma et al., 2003a, 2004; Glick et al., 2014) To study the effect of ACC deaminase on crown gall development, an ACC deaminase gene from the PGPB Pseudomonas putida UW4 was introduced into Agrobacterium tumefaciens C58, so that the effect of ACC deaminase activity on tumour formation in tomato and castor bean plants could be assessed. Plants were also coinoculated with A. tumefaciens C58 and P. putida UW4 or P. putida UW4-acdS- (an ACC deaminase minus mutant strain). In both types of experiments, it was observed that the presence of ACC deaminase generally inhibited tumour development on both tomato and castor bean plant.Different type of bacteria that having the abiliy to produced the de aminase , name of bacteria that produced Acc deaminaseAchromobacter , Azospirillum , Agrobacterium , Achromobacter , Burkholderia , Enterobacter , Pseudomonas and Ralstonian..(Balha et al; 2006)
A wide range of microorganisms preseant in the rhizosphere having the ability to produce substances that regulate plant growth and development. Plant growth promoting rhizobacteria produce phytohormones such as auxins, cytokinins, gibberellins and Ethylene can affect cell proliferation in the root structure by over production of lateral roots and root hairs by increasing of the nutrient and water uptake (Gupta et al ;2015).
Indole acetic acid production ,produced by the combine approach of the chemical and genetic analysis. amyloliquefaciens FZB42 affects its ability to promote plant growth. Moreover, this ability is dependent on the presence of tryptophan, which is one of the main compounds present in several plant exudates (Kamilova et al. 2006,Elsorra et al; 2007). Inactivation of genes involved in tryptophan biosynthesis and in a putative tryptophan-dependent IAA biosynthesis pathway lead to reduction of both IAA concentration and plant-growth-promoting activity in the respective mutant strains (Elsorra et al ;2007). .Indole acetic acid production is a common trait of PGPR, and such bacteria is believed to be act againts the salinity stress in plants.Morphological plant root changes have been observed repeat-edly upon Azospirillum inoculation and have been attributed to the production of plant-growth-promoting substances:auxins, cytokinins, and gibberellins, with auxin production being quantitatively the most important(Spaepen et al.,2008) Streptomyces isolate increased plant growth in wheat and produced indoleacetic acid and auxin in presence of salt (Sadeghi et al., 2012). The genetic mechanism of auxin biosynthesis and regulation by Pseudomonas, Agrobacterium, Rhizobium, Bradyrhizobium, and Azospirillum, are well studied; in these bacteria several physiological effects have been correlated to the bacterial phytohormones biosynthesis (Costacurta et al.,1995).
INDIRECT MECHANISM The major indirect mechanism of plant growth promotion in rhizobacteria is through acting as biocontrol agents Mechanisms of biological control by which rhizobacteria can promote plant growth indirectly, Indirect mechanisms include the biological control of pathogens production of , Hydrogen cyanide (HCN) as well as siderophores which chelate iron and make it available to the plant roots .Particular bacterial strains in certain natural environments prevent infectious diseases of plant roots. During root colonization, these bacteria produce antifungal antibiotics (Hass et al; 2005).
The production of antibiotics(Germs killing drugs) is consider to be one of the most powerful and studied biocontrol mechanisms of plant growth promoting rhizobacteria against phytopathogens has become increasingly better understood over the past twenty year ( Gupta et al; 2015). There are variety of antibiotics have been identified, including compounds such as , oomycin A, phenazine, pyoluteorin, amphisin, 2,4-diacetylphloroglucinol (DAPG), tropolone, and cyclic lipopeptides produced by pseudomonads), pyrrolnitrin, tensin
(Loper et al 2007,Gupta et al; 2015) .One problem associated with this mechanisam is that, depending too much on antibiotic-producing bacteria as biocontrol agents , the increased use of these strains, some phytopathogens may develop resistance to against the specific antibitoics. To prevent this from happening, some researchers have utilized biocontrol strains that synthesize hydrogen cyanide as well as one or more antibiotics, is approach is effective because, while hydrogen cyanide may not have much biocontrol activity by itself, it appears to act synergistically with bacterially encoded antibiotic (Glick et al ;2012). For example, a seed application of a combination of three PGPR, Bacillus pumilus Meyer & Gotheil, Bacillus subtilis (Ehrenberg) Cohn and Curtobacterium flaccumfaciens (Hedges) Collins & Jones provided greater control of several pathogens on cucumber (Cucumis sativa L.) than when any were inoculated singly(Raupach and Kloepper, 1998,Whipps et al; 2001). The antibiotics phenazine-1-carboxylic acid (PCA) and 2,4-diacetylphloroglucinol (Phl) are major determinants of biological control of soil borne plant pathogens by various strains of fluorescent Pseudomonas spp.(raaijmakers ;et al 1997).
Induced systemic resistance (ISR)
Induced systematic resistance came out as an important mechanism by which selected plant growth-promoting bacteria and fungi in the rhizosphere prime the whole plant body for enhanced defense against a broad range of pathogens and insect herbivores nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance SAR (piterse et al; 2014). Rhizobacteria-mediated induced systemic resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species ( L.C von loon et al.,1998). Plant growth promoting rhizobacteria (PGPR) belonging to fluorescent pseudomonads group were isolated from sugarcane rhizosphere. Selected strains were studied for the induced systemic resistance (ISR) against Colletotrichum falcatum Went causing red rot disease in the sugarcane . The talc based formulations of the PGPR strains were prepared and applied through different methods and in different growth phases of the crop in the field. All the tested PGPR strains have significantly reduced the disease development in the stalks (Viswanathan et al; 1999). Specific strains of the species B. amyloliquefaciens, B. subtilis, B. pasteurii, B. cereus, B. pumilus, B. mycoides, and B. sphaericus elicit significant reductions in the incidence or severity of various diseases on a diversity of hosts (Josep,2004). A wide variety of root-associated mutualists, including Pseudomonas, Bacillus, Trichoderma, and mycorrhiza species sensitize the plant immune system for enhanced defense without directly activating costly defense (zamioudi et al ;2014).
Production of the volatile organic compound
volatile organic compounds (VOCs) emission by certain plant-growth promoting rhizobacteria (PGPR) has been found to be involved in plant growth. However, little is known about the role of bacterial VOCs in plant developmental processes (Fransisca et al.,2010) .VOCs, the major source of secondary metabolites and important components in ecosystems , are intensively studied due to their availability as a biocontrol resource (Benthe.,et al 1997,Naznin et al ;2013). VOCs characterized by low molecular weight and high vapor pressure are produced by all organisms as part of their normal metabolism, and play important roles in communication within and between organisms (Santoro MVet al ;2014 Naznin et al ;2013). Many types of bacteria can regulate plant growth from a distance without any contact, suggesting the possibility that these bacteria emit invisible volatile compounds that promote or inhibit plant growth. Nearly 350 bacterial species have been reported to produce around 846 different potential VOCs, with 5431 synonyms ,(Hafiz A et al 2017 : Lemfack et al., 2014). Several bacterials pecies,from diverse generaincludingBacillus,Pseudomonas,Serratia,Arthrobacter,andStenotrophomonas, produce VOCs thatinfluenceplantgrowth.Acetoinand2,3butanediolsynthesized by Bacillus are the best known of these compounds and are responsible for significant improvements in plant growth (Ryu et al ;2003).
Microbial inoculants have long been incorporated into field practices worldwide, with satisfactory results, especially for rhizobia. Plant growth promoting rhizobacteria (PGPR) are a heterogeneous group of bacteria that can be found in the rhizosphere, at root surfaces and in association with roots, which can improve the extent or quality of plant growth directly and/or indirectly. In the direct promotion by PGPR entails either providing the plant with plant growth promoting substances that are synthesized by the bacterium or facilitating the uptake of certain plant nutrients from the environment. The indirect promotion of plant growth occurs when PGPR prevent deleterious effects of one or more phytopathogenic microorganisms. The exact mechanisms by which PGPR promote plant growth are not fully understood, but are thought to include the ability to produce a change in the pattern of growth of the plants.
Ahemad, M and Kibret, M. (2014) Mechanisms and applications of plant growth promoting rhizobacteria: Current perspective. J of King Saud University – Science, 26(1):1–20
Ahmed ,M. (2015). Phosphate-solubilizing bacteria-assisted phytoremediation of metalliferous soils. A review of biotechnology, 5(2): 111–121
Ahmed ,M and khan, M.S. 2012 .Evalaution of plant growth promoting activities of rhizobacterium pseudomonas putida under herbicide stress .Ann .microbiology ,62(4):1531_1540
Ali, S.S , N.N and Vidhale. (2013). Bacterial Siderophore and their Application a review.Int.J.Curr. Microbiol.App.Sci , 2(12): 303-312.
Araujo ,W.L, Marcon ,J., Maccheroni ,W., Van, Elsas., J.D ,J.r.,Van and Vuurde, J.W.L. (2002) Diversity of endophytic bacterial populations and their interaction with Xylella fastidiosa in citrus plants. Appl Environ Microbiol ,68(10): 4906-4914.
Adesemoye ,T and Egamberdieva ,D. (2013). Beneficial Effects of Plant Growth-Promoting Rhizobacteria on Improved Crop Production: Prospects for Developing Economies. Springer science 50(25) :507.
Bashan, Y. (1998). Inoculents of plants growth-promoting bacteria for use in agriculture. Department of Microbiology.Biotechnology advances 16(4):729_770.
Bunge, M., Araghipour, N., Mikoviny, T., Dunkl, J., Schnitzhofer ,R., Hansel, A., Schinner F., Wisthaler A., Margesin, R and Märk, T.D. (2008). On-line monitoring of microbial volatile metabolites by proton transfer reaction–mass spectometry. Appl Environ Microb, 74(7):2179–2186
Baily, A and weiskopf .(2012).The modulating effect of bacterial volatiles on plant growth. journal
Plant Signaling & Behavior, 7(1) :79_58
Bablola. (2010). Benificil bacteria of agricultural importance.Biotechnol Lett,32(11): 1559-70.
Babu,Khan ,S., Yeo, C.T .,Martin, W.L., Duron, M.R., Rogers, R.D and Goldstein A.(1995).Cloning of a mineral phosphate solubilizing gene from Pseudomonas cepacia, Appl. Environ. Microbiol; 61(3) : 972–978
Beneduze, A.,Ambrosini., A, and passagalia, L. (2012).Plant growth-promoting rhizobacteria (PGPR): Their potential as antagonists and biocontrol agents.jouranal of genetic molecular biology. 35(4): 1044–1051
Benson, D .R and Silvester W .B, (1993) Biology of Frankia strains, actinomycete symbionts of actinorhizal plants.Micarobiological review ;57(2): 293–319.
Blaha ,D., Prigent,Combaret, C and Mirza ,M.S.(2006). Phylogeny of the 1-aminocyclopropane-1-carboxylic acid deaminase-encoding gene acdS in phytobeneficial and pathogenic Proteobacteria and relation with strain biogeography. FEMS Microbiol Ecol. ;56(3):455–470
Braud , A ., Jazeque, K.,Bazot, S and Lebeau ,T .(2009).Enhanced phytoextraction of an agricultural Cr- and Pb-contaminated soil by bioaugmentation with siderophore-producing bacteria. Journal of elsewhere science 74(2): 280-286
Bashan, Y., de .Bashan, L.,S. R. Prabhu.,Pablo and Hernande ,J .(2014). Advances in plant growth-promoting bacterial inoculant technology: formulations and practical perspectives (1998–2013) .plant soil ,378(1_2):1_3
Bhat, A .T ., Ahmad, L., Ganai ,M .A., Haq, S .u and Khan ,A .O .(2015). Nitrogen Fixing Biofertilizers; Mechanism and Growth Promotion.Journal Of Pure and applied microbiology , 9(2). 1675-1690
Benthey, R.1997 .Secondary metabolites play primary roles in human affairs ,Prospect Biol Med. 40:197–221
Compant, S.W., Duffy ,B., Nowak, J., Clement ,C and Barka, E.A .(2005). Use of plant growth-promotingbacteria for biocontrol of plant diseases: principles, mechanisms of action, and future prospects. Appl Environ Microb , 71(9) :4951– 4959
Crosa, J.H and Walsh, C.T.(2002). Genetics and assembly line enzymology of siderophore biosynthesis in bacteria. Microbiol Mol Biol Rev ,66(2) :223–249
Cocking, A. C .(2003) . Endophytic colonization of plant roots by nitrogen-fixing bacteria.review of plant and soil ,252(1).169_175
Chaturvedi ,H., Singh, V .,and Gupta, G .(2016) Potential of Bacterial Endophytes as Plant Growth Promoting Factors.journal of plant pathology and microbiology .7:(9) 10.4172/2157-7471.1000376
D.M, Moffatt. B.A and Glick B.R.(2001) Determination of -aminocyclopropane-1-carboxylic acid (ACC) to assess the effects of ACC deaminase-containing bacteriaon roots of canola seedlings. Can J Microbiol ;47:77–8
Défago, G., Hass and D. (2005).Biological control of soil-borne pathogens by fluorescent Pseudomonas. Nature Rev micarobilogy ,3(4):307–19
Date, R.A .(2001) Advances in inoculant technology: a brief review. Aust J Exp Agr ,41(3):321–325
Dias, A, Santos ,S.G, Vasconcelos ,VGS., Radl, V., Xavier ,G.R., Rumjanek ,N.G and Ribeiro, R.L. (2013). Screening of plant growth promoting rhizobacteria for the development of vegetable crops inoculants. Afr. J. Microbiol. Res, 7(19):2087-2092L
Egamberdieva ,D and Kucharova ,Z.2009 Selection for root colonising bacteria stimulating wheat growth in saline soils. Biology and Fertility of Soils,45(6):563–71
ElSorra, E. Idris,1Domingo, J. Iglesias., Talon, M and B. Rainer. (2007).Tryptophan-Dependent Production of Indole-3-Acetic Acid (IAA) Affects Level of Plant Growth Promotion by Bacillus amyloliquefaciens FZB42. The American Phytopathological Society 20(6):619_626
Fraile ,G.P,Menendez and E,Rivas, R.(2015) Role of bacterial biofertilizers in agriculture and forestry.aims bioengineering ,2(3).183_205
F.Pérez.,Montaño, C.Alías.,Villegas ,R.A.Bellogín .,P.del Cerro M.R.EspunyI.Jiménez-GuerreroF.J.,López,BaenaF.J and OlleroT.Cubo (2014)Plant growth promotion in cereal and leguminous agricultural important plants: From microorganism capacities to crop production. journal of micarobiological research 169(5_6):325_326
Fransica , M.,Luna G.,Bucio j.p,Hernadez j .A,canter VE and DE la cruz R.h (2010). Plant growth-promoting rhizobacteria modulate root-system architecture in Arabidopsis thaliana through volatile organic compound emission.Iternationl weekly journal of science .51(1) :75_83
Gupta, G., Parihar ,S., Kumar, Ahirwar, N., Kumar ,Snehi , Sand and Singh v.(2015). Plant Growth Promoting Rhizobacteria (PGPR): Current and Future Prospects for Development of Sustainable Agriculture. Journal of Microb Biochem Technology 7(2):96_102
Gilck, B.R., Patten, C.L., Holguin, G., and Penrose D.M .(1999). Biochemical and genetic mechanisms used by plant growth promoting bacteria. Imperical college press, London, pp.187-189
Glick, B.R (1995). Enhancement of plant growth by free living bacteria. Candian Journal of Microbiol, 41(2): 109-117
Glick, B.,(2012) .Plant Growth-Promoting Bacteria: Mechanisms and Applications Hindawi Publishing Corporation. review of Scientica.(2012):1_15 ID 963401_ 15 http://dx.doi.org/10.6064/2012/963401
Glick ,B.,Cheng Z., Czarny, J and Duan, j.(2007) Promotion of plant growth by ACC deaminase-producing soil bacteria.eurpion journal of plant pathology;119(3):329_339
Glick, B.R.(2014) Bacteria with ACC deaminase can promote plant growth and help to feed the world. Review of Microbiological Research 169(1):30_39
Gururani, M.A., Upadhyaya ,C.P and Baskar, v. (2012). Plant growthpromoting rhizobacteria enhance abiotic stress tolerance in Solanum tuberosum through inducing changes in the expression of ROS-scavenging enzymes and improved photosynthetic performance. J Plant Growth Regul ;32:245–58
Goldstein and Alan., H .(1986). Bacterial solubilization of mineral phosphates: Historical perspective and future prospects. American Journal of Alternative Agriculture.1(2):51_57
Ghany, T. M .A., Alawlaqi., M .M. and Abboud, M .A.A. (2013) Role of biofertilizers in agriculture: a brief review of mycopathology . 11(2): 95- 101
Gray, E.J., Smith and D.L.,(2005) Intracellular and extracellular PGPR: Commonalities and distinctions in the plant-bacterium signaling processes. Soil Biol Biochem, 37(3):395–412.
Hao, Y.charless ,T.C and Glick ,B.R.(2007) ACC deaminase from plant growth-promoting bacteria affects crown gall development.Can J microbiology . 53(12):1291-9
Hafiz, A. S.,Tahir, Qin., G.u, Huijun W.u, Raza, W..,Hanif, A.,Liming ,Wu., Massawe and,V.Colman, Gao(2017)P lant Growth Promotion by Volatile Organic Compounds Producedby Bacillussubtilis SYST2.JOURNALoffrontmicrobiology,8(171):https://dx.doi.org/10.3389%2Ffmicb.2017.00171
Insam, H., & Martin, S. A.and Seewald.(2010) Volatile organic compounds (VOCs) in soils.bio fertile soil 46:199–213
Hayat, R, Ali , S., Amara, U ., Khalid, R and Ahmed, I.(2010) .Soil beneficial bacteria and their role in plant growth promotion a review.Annu microbiology. 60(4) :579_578.
Hass, D and Defago, G. (2005).Biological control of soil borne pathogen by fluorescence peudomonads.Nat rev Micarobiol, 3(4):307_319
Joshi, K.K., Kumar, V., Dubey, R.C and Maheshwari, D.K .(2006) .Effect of chemical fertilizer adaptive variants, Pseudomonas aeruginosa GRC2 and Azotobacter chroococcum AC1 on Macrophomena phaseolina causing charcoal rot of Brassica juncea. Korean J Environ Agric 25(3): 228-235
Jiang ,C.Y, Sheng, X.F., Qian ,M and Wang, Q.Y.(2008). Isolation and characterization of a heavy metal resistant Burkholderia sp. from heavy metal-contaminated paddy field soil and its potential in promoting plant growth and heavy metal accumulation in metal polluted soil. A review of Chemosphere. ;72 (2):157–164.
J.m raaijmakers,D.M .,weller,L,S and Thomas, show.(1997) .Frequency of Antibiotic-Producing Pseudomonas spp. in Natural Environments.review of apllies enviormental microbiology ;63(3):881_887
joseph, B., Patra, R.R and , Lawrence, R., 2007. Characterization of plant growth promoting rhizobacteria associated with chickpea(Cicer arietinum L.). Int. J. Plant Prod, 1 (2) :141–152
Jahanian, A., Chaichi, M.R., Rezaei, K., Rezayazdi, K and Khavazi, K.,2012. The effect of plant growth promoting rhizobacteria (pgpr) on germination and primary growth of artichoke (Cynara scolymus),Int. J. Agric. Crop Sci. 4(14) : 923–92
Jan, S.,kamili, A., Egamberdieva, D and Ahmed, P.(2016). Current Perspectives on Plant Growth-
Promoting Rhizobacteria. Journal of Plant Growth Regulation;journal of the springer science :1_29
Kloepper ,J.W and Schroth ,M.N (1981). Plant growth-promoting rhizobac-teria and plant growth under gnotobiotic conditions. Phytopathology ,71(6) :642–644.
Kumar, P., Satyanarayana, S. (2012) .Liquid Microbial Consortium- A Potential Tool for Sustainable Soil Health. J Biofertil Biopestici, 3(43) http://dx.doi.org/10.4172/2155-6202.1000124
Kumar, V., Behl, R.K and Narula, N.( 2001). Establishment ofphosphate solubilizing strains of Azotobacter chroococcum in therhizosphere and their effect on wheat cultivars under greenhouseconditions. Review of Microbiol. Res;156(1) : 87–9
Karnwal, A .(2017) .Isolation and identification of plant growth promoting rhizobacteria from maize (Zea mays L.) rhizosphere and their plant growth promoting effect on rice (Oryza sativa L.) ,jornal of plant protection and research;57(2) : https://doi.org/10.1515/jppr-2017-0020
Katiyar ,D., Hemantaranjan A and Singh B (2016) Plant Growth Promoting Rhizobacteria-an Efficient Tool for Agriculture Promotion. Adv Plants Agric Res, 4(6): 00163. DOI: 10.15406/apar.2016.04.00163
Kamilova, F., Kravchenko, L. V., Shaposhnikov, A. I., Azarova, T., Makarova, N., and Lugtenberg, B. (2006). Organic acids, sugars, and Ltryptophane in exudates of vegetables growing on stonewool and their effects on activities of rhizosphere bacteria. Mol. Plant-Microbe Interact.19:250-256.
Kumar c, Saraf M(2015) Plant growth promoting Rhizobacteria (PGPR). E3 Journal of Agricultural Research and Development Vol. 5(2). pp. 0108-0119
Loper, J.E and Gross, H .(2007). Genomic analysis of antifungal metabolite production by Pseudomonas fluorescens Pf-5. Eur J Plant Pathol 119: 265-278
Litwin, C.M., and Calderwood, S.B. 1993. Role of iron in regulation of virulence genes. Clin. Microbiol. Rev,6(2): 137-149
- C. van., Loon, P. A. H. M. Bakker, and C. M. J. Pieterse .1998 Systematics Resistancve Induced by rhizosphere bacteria . Annu. Rev. Phytopathol.36:453_83
L ucy M, Reed E, Glick ,B.R .(2004). Applications of free living plant growth-promoting rhizobacteria. Antonie Van Leeuwenhoek. Int. J. Gen. Mol. Microbiol, 86(2): 1-25
Lemfack ,M .C., Nickel J., Dunkel ,M., Preissner , R and Piechulla, B. (2014). MVOC: adatabase of microbial volatiles. Nucleic Acid Res. 1(42) :744–748. 10.1093/nar/gkt1250
Mariano, I ., Valverdea, A ., Cervante, san ,E and Velazquezb, E .(2001). Phosphate-solubilizing bacteria as inoculants for agriculture: use of updated molecular techniques in their study. Re view of agronomie, 21(6_7)561_568
Madhaiyan, M., Poonguzhali, S., Kang, B.G., Lee, Y-J., Chung, J.B and Sa, T.M.( 2010). Effect of co-inoculation of methylotrophic Methylobacterium oryzae with Azospirillum brasilense and Burkholderia pyrrocinia on the growth and nutrient uptake of tomato, red pepper and rice. Plant Soil 328 (1_2) : 71-82
Mahmmod A,Turgay O.C,Farooq and M .Seed (2016) biopriming with plant growth promoting rhizobacteria: A review FEMS Microbiology Ecology.92(8):doi: 10.1093/femsec/fiw112
Ma ,W, Sebestianova., S, Sebestian J., Burd G.I., Guinel F and Glick B.R.(2003) Prevalence of 1- aminocyclopropaqne-1-carboxylate in deaminase in Rhizobia spp. Anton Leeu wb;83:285–91
Ma ,W, Charles T.C and Glick, B.R(2004) Expression of an exogenous 1-aminocyclopropane- 1-carboxylate deaminase gene in Sinorhizobium meliloti increases its ability to nodulate alfalfa. Appl Environ Microbiol ,70(10):589 1–7
Malik ,K. A ,Bilal R ,Mehnaz S, Rasul G, Mirza M .S and Ali S .(1997). association of nitrogen fixing plant promoting rhizobacteria ( PGRP) with kallar grass and the soil .j of springer scince.30(50):433_439.
M., X. Liu , S. Gavriel, Z. Ismailov, I. Chet, and L. Chernin. (2004). The global regulator genes from biocontrol strain Serratia plymuthica IC1270: cloning, sequencing, and functional studies, J. Bacteriol. 186(15):4986-4993
- Schoebitz. , C. Ceballos. and L. Ciampi (2013) .Effect of immobilized phosphate solubilizing bacteria on wheat growth and phosphate uptake. Journal of Soil Science and Plant Nutrition .13 (1): 1-10
Naznin A.H.,Kimura M.,Miyazwa and M,Hyakumachi M,(2013) Analysis of Volatile Organic Compounds Emitted by Plant Growth-Promoting Fungus Phoma sp. GS8-3 for Growth Promotion Effects on Tobacco.jouranl of microbes enviorment.28(1):42_49
Nobbe,F & Hitliner,L.(1896) inoculation of soil for cultivating leguminous plant u.s patent 570_813
Okon ,y.,(1985). Azospirillum as a potential inoculant for agriculture.Review of trend in bio technology,3(9):223_228
Parray j , Jan S, Kamili A, .Qadri R, Egamberdieva and D ,Ahmad P .(2016) .Current Perspectives on Plant Growth-Promoting Rhizobacteria:journal of plant growth regulation 35(1): 1_302
PA, Roger. (1986) .Technologies for utilizing biological nitrogen fixation in wetland rice :potentialities ,current usage ,and limiting factor ,fertilizer research ;9(1_2):39_77
Induced systemic resistance by beneficial microbes.ann rev of plant pathology . 52:347-75
Ryu, C.M.; Farag, M.A.; Hu, C.H.; Reddy, M.S.; Wei, H.X.; Paré, P.W and Kloepper, J.W.(
2003) Bacterial volatiles promote growth in Arabidopsis. Proc. Natl. Acad. Sci. USA , 100(8) :4927–4932.
.Rodríguez , H and Fraga ,R.(1999). Phosphate solubilizing bacteria and their role in plant growth promotion.biological advance research review paper;17(4_5):319_339
Raupach ,G.S and Kloepper, J.W.1998. Mixtures of plant growth-promoting rhizobacteria enhance biological control of multiple cucumber pathogens. Phytopathology; 88(11):1158–1164
Ramadan ,A. E., Ahmed, A.l HafezA ., Enas, A. Hassan and Fekria M. Saber.,(2016). Plant growth promoting rhizobacteria and their potential for biocontrol of phytopathogens. African Journal of Microbiology Research.10(15) 486-504, 21
Rojas, M. J., Caballero and Mellado, J, (2003) Population dynamics of Gluconacetobacter diazotrophicus in sugarcane cultivars and its effect on plant growth. Microb Ecol 46(4): 454–,
- Viswanathan and R. Samiyappan.(1999) Induction of systemic resistance by plant growth promoting rhizobacteria against redroot disease in sugarcane.sugartechnology.1(67) :https://doi.org/10.1007/BF02945166
Smith, R.S. (1992). Legume inoculant formulation and application. Can. J. Microbiol.;38(6): 485-492
Souza D,Ambrosini A ,and Passagalia L.(2015) .plant growth promoting bacteria as inoculants in agricultural soil,journal of genetics and molecular biology; 38(4):401_419
Spaepen, S., Dobbelaere ,S, Croonenborghs A and Vanderleyden J (2008)Effects of Azospirillum brasilense indole-3-acetic acid productionon inoculated wheat plants. Plant Soil 312(1–2):15-23
Stahl, P.D and Parkin T.B (1976) Microbial production of volatile organic compounds in soil microcosms. Soil Sci Soc Am J 60:821–828
Saleem M, Arshad M, Hussain S, and Saeed Bhatti A.(2007). Perspective of plant growth promoting rhizobacteria (PGPR) containing ACC deaminase in stress agriculture.Journal of industrial microbiology and biotecnology ,34(10).:635_638
Steenhoudt O and Vanderleyden (2000) Azospirillum, a free-living nitrogen-fixing bacterium closely associated with grasses: genetic, biochemical and ecological aspectsFEMS Microbiology Reviews .24(4) :487–506
Schoebitz M.,. López M.D & Roldán A.(2013). Bioencapsulation of microbial inoculants for better soil–plant fertilization. A review. Agron. Sustain. Dev. 33:751–765
Sathya, A., Vijayabharathi ,R. and Gopalakrishnan ,S.(2017) Plant growth-promoting actinobacteria: a new strategy for enhancing sustainable production and protection of grain legumes.journal of biotechnology 7(2):.doi: 10.1007/s13205-017-0736-3
Stephens J.H.G and Rask HM (2000) Inoculant production and formulation. Field Crops Res 65 (2_3):249–258
Spaepen ,S., Dobbelaere, S., Croonenborghs, A and Vanderleyden ,J. (2008)Effects of Azospirillum brasilense indole-3-acetic acid productionon inoculated wheat plants. Plant Soil 312(1–2):15-23
Santoro ,M.V, Zvgadlo, J., Giordano ,W and Banchio, E.(2011). Volatile organic compounds from rhizobacteria increase biosynthesis of essential oils and growth parameters in peppermint (Mentha piperita) Plant Physiol Biochem. 49(10):1177–1182
- Vermeiren, H., Willems, A., Schoofs, G., de, Mot ,R., Keijers ,V., Hai ,W and Vanderleyden, J. 1999. The rice inoculant strain Alcaligenes faecalis A15 is a nitrogen-fixing Pseudomonas stutzeri. Systematic and Applied Microbiology22(2): 215–224.
Vansuyt G, Robin A, Briat JF, Curie C and Lemanceau P .(2007). Iron acquisition from Fe-Pyoverdine by Arabidopsis thaliana . Mol Plant Microbe Interact .20(4):441–447
Velázquez,Becerra C., Macias ,Rodriguez ,L.I., Lopez,Bucio, J, Altamirano,Hernandez J, Flores,Cortez I, and Valencia-Cantero E.(2011)A volatile organic compound analysis from Arthrobacter agilis identifies dimethylhexadecylamine, an amino containing lipid modulating bacterial growth and Medicago sativa morphogenesis in vitro. Plant Soil;3 (39):329–40.
Vermeiren, H., Willems ,A., Schoofs ,G., de, Mot, R., Keijers, V., Hai, W and Vanderleyden J. 1999. The rice inoculant strain Alcaligenes faecalis A15 is a nitrogen-fixing Pseudomonas stutzeri. Systematic and Applied Microbiology 22(2): 215–224 R. s
Viswanathan, R and Samiyappan.(1999) Induction of systemic resistance by plant growth promoting rhizobacteria against red rot disease in sugarcane.sugar technology,springer india.1(67). https://doi.org/10.1007/BF02945166
Whipps, J.(2001). Microbial interactions and biocontrol in the rhizosphere. Journal of Experimental Botany ;52(1_1) 487–511
Wu, Z., Guo, L., Qin, S and Li, C. 2012. Encapsulation of R. planticola Rs-2 from alginate-starch-bentonite and its controlled release and swelling behavior under simulated soil conditions. J. Ind. Microbiol. Biotechnol. 39(2), 317-27
Wang W, Qiu Z, Tan H, Cao L.(2014) Siderophore production by actinobacteria. Biometals. ;27(4):623–631.
Yoram, Kapulnik, Y., , Okon, Y., and , Henis Y .(1985).Changes in root morphology of wheat caused by Azospirillum inoculation. Canadian Journal of Microbiology.;31(10): 881-887
Youssef, M.M.A, Eissa, M.F.M. (2014). Biofertilizers and their role in management of plant parasitic nematodes. E J Biotechnol Pharm Res; 5(1)6: .001-006.
Zafar _ul-Hye M ., Muhammad, Farooq ,H ., and Hussain ,M .,(2015) Bacteria in combination with fertilizers promote root and shoot growth of maize in saline-sodic soil.Braz J micarobilogoy; 46(1): 97–102
Zaidi, M. S. Khan, M., Ahemad & M.Oves .(2009) .Plant Growth Promotion by Phosphate Solublisng Bacteria. Microbiologica et Immunologica Hungarica; 56 (3), 263–284. DOI: 10.1556/AMicr.56.2009.3.6
Zamioudis ,C, and van wees S(2014) induced systematic reistance by the beneficial microbes.annual review of phytopthology,52:347_75
Zahir, Z. A., Asghar, H. N., Akhtar, M. J. and Arshad, M. (2005). Precursor (L-tryptophan)-inoculum (Azotobacter) interaction for improving yields and nitrogen uptake of maize. Jouranal of Plant Nutrition, 2: 805-817