Plant growth-promoting traits of biocontrol potential bacteria isolated from rice rhizosphere.pdf
RESEARCH Open Access Plant growth-promoting traits of biocontrol potential bacteria isolated from rice rhizosphere Subramaniam Gopalakrishnan1*, HD Upadhyaya1, Srinivas Vadlamudi1, Pagidi Humayun1, Meesala Sree Vidya1, Gottumukkala Alekhya1, Amit Singh2, Rajendran Vijayabharathi1, Ratna Kumari Bhimineni1, Murali Seema1, Abhishek Rathore1 and Om Rupela1 Abstract Seven isolates of bacteria (SRI-156, SRI-158, SRI-178, SRI-211, SRI-229, SRI-305 and SRI-360) were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum and plant growth promotion (PGP) of the plant. In the present study, the seven isolates were characterized for their physiological traits (tolerance to salinity, pH, temperature and resistance to antibiotics and fungicides) and further evaluated in the field for their PGP of rice. All the seven isolates were able to grow at pH values between 5 and 13, in NaCl concentrations of up to 8% (except SRI-156 and SRI-360), temperatures between 20 and 40°C and were resistant to ampicillin (>100 ppm; except SRI-158 and SRI-178) but sensitive (<10 ppm) to chloramphenicol, kanamycin, nalidixic acid, streptomycin (except SRI-156 and SRI-211) and tetracycline. They were tolerant to fungicides benlate and captan, except SRI-158 and SRI-178, bavistin and sensitive to thiram (except SRI-156 and SRI-211) at field application level. In the field, four of the seven isolates (SRI-158, SRI-211, SRI-229 and SRI-360) significantly enhanced the tiller numbers, stover and grain yields, total dry matter, root length, volume and dry weight over the un-inoculated control. In the rhizosphere soil at harvest, all the isolates significantly enhanced microbial biomass carbon (except SRI-156), microbial biomass nitrogen and dehydrogenase activity (up to 33%, 36% and 39%, respectively) and total N, available P and% organic carbon (up to 10%, 38% and 10%, respectively) compared to the control. This investigation further confirms that the SRI isolates have PGP properties. Keywords: Biocontrol, Plant growth promotion (PGP), Rice, Field evaluation, Rhizosphere bacteria Introduction Plant growth −promoting rhizobacteria (PGPR) are the soil bacteria that colonize the roots of plants and en- hance plant growth. PGPR can directly or indirectly affect plant growth through various mechanisms. Direct stimulation may include fixation of atmospheric nitrogen (Soares et al. 2006), synthesis of various phytohormones and enzymes (Patten and Glick 2002; Penrose and Glick 2003; Cheng et al. 2007) and solubilization of minerals in plants (Basak and Biswas 2009; Panhwar et al. 2012), while indirect stimulation includes inhibiting phyto- pathogens (Hao et al. 2011). Actively growing microbes are greater in number in the rhizosphere as crop plants release root exudates that produce, in addition to simple and complex sugars and growth regulators, different classes of primary and secondary compounds including amino acids, organic acids, phenolic acids, flavonoids, fatty acids, enzymes, steroids, alkaloids and vitamins (Uren 2000). Researchers around the world attempted to isolate PGPR organisms from the rhizospheres of crop plants. Seven isolates of bacteria (SRI-156, SRI-158, SRI-178, SRI-211, SRI-229, SRI-305 and SRI-360), isolated from the rhizospheres of a system of rice intensification (SRI) fields, were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum, caused by Macro- phomina phaseolina (Tassi) Goid. and plant growth pro- motion (PGP) of the plant (Gopalakrishnan et al. 2011a). Also, the selected bacterial strains produced siderophore, indole acetic acid (except SRI-305), hydrocyanic acid (except SRI-158 and SRI-305) and solubilized (except SRI-360) phosphorous (Gopalakrishnan et al. 2011a). In * Correspondence: s.gopalakrishnan@cgiar.org 1International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh, India Full list of author information is available at the end of the article a SpringerOpen Journal © 2012 Gopalakrishnan et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Gopalakrishnan et al. SpringerPlus 2012, 1:71 http://www.springerplus.com/content/1/1/71 the SRI method of rice cultivation, certain changes are done in the agronomic practices which include the use of much younger seedlings than are normally trans- planted, planting them singly and carefully in a square pattern with wide spacing in soil that is kept moist but not continuously flooded and with increased amend- ments of organic matter and active aeration of the soil during weed control operation preferably with mechan- ical weeder (Uphoff 2003). The aim of the present study was to characterize and evaluate the PGP potential of seven SRI strains of bacteria in rice, grown under field conditions using the SRI protocols. It was also aimed to evaluate the potential of these PGP strains enhancing tolerance to salinity, pH, high temperature and resist- ance to antibiotics and fungicides. Materials and methods SRI bacterial isolates A total of seven bacteria isolated from rhizosphere of a SRI fields, SRI-156 (Pseudomonas plecoglossicida; NCBI Accession Number: JQ247008), SRI-158 (Brevibacterium antiquum; NCBI Accession Number: JQ247009), SRI- 178 (Bacillus altitudinis; NCBI Accession Number: JQ247010), SRI-211 (Enterobacter ludwigii; NCBI Acces- sion Number: JQ247011), SRI-229 (E. ludwigii; NCBI Accession Number: JQ247012), SRI-305 (Acinetobacter tandoii; NCBI Accession Number: JQ247013) and SRI- 360 (P. monteilii; NCBI Accession number: JQ247014), reported earlier by us as potential for biocontrol and PGP traits in sorghum (Gopalakrishnan et al. 2011a), were further studied in this investigation. Evaluation of SRI isolates for their physiological traits Salinity SRI isolates were streaked on Luria Bertani (LB) agar with various concentrations of NaCl ranging from 0% to 10% at the interval of 2% and incubated at 28°C for 72 h. pH The seven SRI isolates were streaked on LB agar, adjusted to pH 5, 7, 9, 11 and 13 and incubated at 28°C for three days. For pH 3, LB broth was inoculated with the seven SRI strains and at the end of 72 h incubation the intensity of growth was measured at 600 nm in a spectrophotometer. Temperature The seven SRI isolates were streaked on LB agar and incubated at 20, 30 and 40°C for 72 h. For 50°C, the LB broth was inoculated with the seven SRI strains, and at the end of 72 h incubation, the intensity of growth was measured at 600 nm in a spectrophotometer. Antibiotic resistance/susceptible pattern A total of six antibiotics viz. ampicillin, chloramphenicol, kanamycin, nalidixic acid, streptomycin and tetracycline were studied for their resistance/susceptible pattern against the seven SRI isolates. The required quantities of antibiotics were dissolved in sterilized Milli Q water and mixed into Nutrient agar just before pouring into the Petri plates (when the temperature of the media was about 50°C). Upon solidification, the SRI isolates were streaked and incubated at 28°C for 72 h. Fungicide tolerance SRI isolates were evaluated for their tolerance to fungicides at field application level. A total of four fungi- cides viz. benlate (benomyl 50%; methyl [1-[(butylamino) carbonyl]-1H-benzimidazol-2-yl] carbamate), captan (captan 50%; N-trichloromethylthio-4-cyclohexene-1, 2-dicarboximide), bavistin (carbindozim 50%; methyl benzimidazol-2-ylcarbamate) and thiram (dimethylcar- bamothioylsulfanyl N, N-dimethylcarbamodithioate) were evaluated at field application levels at 3000, 2500, 4000, 3000 and 3000 ppm concentrations, respectively. The required quantities of fungicides were dissolved in steri- lized Milli Q water and mixed into LB agar just before pouring into the Petri plates. Upon solidification, the SRI isolates were streaked and incubated at 28°C for 72 h. Responses of the seven SRI isolates to salinity, pH, temperature, antibiotics and fungicide tolerance were recorded as follows: - = no growth; + = slight growth; ++ = moderate growth and +++ = good growth. Evaluation of SRI isolates for PGP traits on rice under field conditions Study site The experiment was conducted in Kharif 2011 (wet sea- son) at ICRISAT, Patancheru, Andhra Pradesh, India (17o53”N latitude, 78o27”E longitude and 545 m altitude) with a medium duration rice variety, Sampada (135 days).. Soils at the experimental site are classified as sandy loam in texture (55% sand, 17% silt and 28% clay) with alkaline pH of 8.5 −9.0. The mineral content of the top 15 cm layer were as follows: available nitrogen 292 kg ha-1, available phosphorus 26 kg ha-1, available potassium 527 kg ha-1 and organic carbon 0.76 −1.27%. Design and treatments The experiment was laid out in a randomized complete block design (RCBD) with three replicates and 10 m × 7.5 m subplots. Rice was grown by the system of rice in- tensification (SRI) method proposed by the Central Rice Research Institute (http://crri.nic.in). The seven SRI iso- lates were grown on a LB broth at 28°C for three days and further evaluated for their PGP traits. The control contained no SRI isolates. Gopalakrishnan et al. SpringerPlus 2012, 1:71 Page 2 of 7 http://www.springerplus.com/content/1/1/71 which the SRI isolates enhanced the morphological observations could be their PGP attributes such as in- dole acetic acid (IAA), siderophore production and phosphate solubilization (Gopalakrishnan et al. 2011a). IAA −producing microorganisms are known to pro- mote root elongation and plant growth (Patten and Glick 2002), while siderophore producers act by binding Fe3+ from the environment and making it available to the plant (Wang et al. 1993). Free-living phosphate- solubilizing microbes release phosphate ions from spar- ing soluble inorganic and organic P compounds in soils and thereby contribute to an increased soil phosphate pool available for the plants (Artursson et al. 2006). The interaction between soil microorganisms and roots and their possible impacts on plant growth have been studied by Birkhofer et al. (2008) and Uphoff et al. (2009). When the soils were made wet and then dry, as in the case of the SRI method of rice cultivation, the levels of available P in the soil solution increased between 185% and 1900% as a result of population dynamics of species of phosphate-solubilizing bacteria and fungi (Turner and Haygarth 2001). Gayathry (2002) found that the counts of bacteria, such as the diazo- trophs, Azospirillum, Azotobacter and phosphobacteria Table 2 Effect of SRI isolates on the morphology and yield potential of rice cultivation No. of Stover Grain Total dry tillers yield yield matter Treatment (m-2) (g m-2) (g m-2) (g m-2) SRI-156 360 558 540 1098 SRI-158 523 685 643 1328 SRI-178 571 635 583 1218 SRI-211 470 663 595 1258 SRI-229 538 684 673 1357 SRI-305 662 605 628 1233 SRI-360 453 683 650 1333 Control 451 604 582 1186 Mean 504 640 612 1251 SE± 31.6*** 19.7** 17.5** 30.0*** LSD (5%) 91.8 59.8 53.1 90.9 CV% 14 5 5 4 SE = standard error; LSD = least significant difference; CV = coefficient of variance; * = statistically significant at 0.05; ** = statistically significant at 0.01; *** = statistically significant at 0.001. Table 3 Effect of SRI isolates on the root development of rice at harvesting stage of rice cultivation Root length (mm-2) Root volume (cm3 m-2) Root dry weight (g m-2) Treatment 0 −15 cm 15 −30 cm 0 −15 cm 15 −30 cm 0 −15 cm 15 −30 cm SRI-156 5312 996 901 152 63.9 8.2 SRI-158 4979 711 859 106 60.2 5.9 SRI-178 5230 817 839 107 59.9 6.6 SRI-211 6542 781 1183 189 82.9 8.6 SRI-229 6389 922 1120 117 89.2 6.4 SRI-305 5004 887 903 112 66.9 6.4 SRI-360 5036 800 1065 112 72.9 6.7 Control 5019 509 840 89 47.1 5.6 Mean 5413 783 953 118 68.9 6.6 SE± 164.9*** 87.1* 27.7*** 11.1** 4.7** 1.1 NS LSD (5%) 516.9 274.2 86.9 35.3 14.9 - CV% 4.6 16.9 4.4 13.9 10.4 25.1 SE = standard error; LSD = least significant difference; CV = coefficient of variation; NS = not significant; * = statistically significant at 0.05; ** = statistically significant at 0.01; *** = statistically significant at 0.001. Table 4 Effect of SRI isolates on soil biological activity at harvesting stage of rice cultivation Microbial Microbial Dehydrogenase biomass carbon biomass nitrogen activity (μg TPF g-1 Treatment (μg g-1 soil) (μg g-1 soil) soil 24 h-1) SRI-156 2625 62 115 SRI-158 2876 71 120 SRI-178 3448 67 152 SRI-211 3129 80 133 SRI-229 3050 68 142 SRI-305 3776 75 131 SRI-360 3774 74 154 Control 2845 58 111 Mean 3190 69 132 SE± 177.3** 2.2*** 8.6* LSD (5%) 567.2 7.0 26.1 CV% 10 5 11 SE = standard error; LSD = least significance difference; CV = coefficient of variance; * = statistically significant at 0.05; ** = statistically significant at 0.01; *** = statistically significant at 0.001. Gopalakrishnan et al. SpringerPlus 2012, 1:71 Page 5 of 7 http://www.springerplus.com/content/1/1/71 and microbial enzyme activity such as dehydrogenase, urease acid phosphatase, alkaline phosphatase and nitrogenase were significantly higher in SRI rhizospheres than those of the same variety of rice plants grown con- ventionally. In the present investigation, such enhanced activities were found only in the SRI isolates-inoculated treatments. Colonization of roots by SRI isolates at the right place and time is essential for enhanced PGP activity. Success- ful interactions depend on sufficient population density, rhizosphere competence, root colonizing ability and PGP ability of the bacteria (Lugtenberg and Dekkers 1999). Although roots were not inspected for colonization in this study, the data on morphological (including roots), biological and chemical studies strongly suggest that SRI isolates had multiplied and colonized the inoculated rice roots. Hence, it can be concluded that the seven SRI isolates used in this study were apparently well adapted to the rice rhizosphere environment and enhanced the plant growth. The seven isolates of SRI used in this study were apparently well adopted not only in the sorghum rhizo- sphere environment (Gopalakrishnan et al. 2011a) but also in the rice rhizosphere where they promoted plant growth. Hence, these isolates could be used as PGP agents in addition to biocontrol agents for the control of charcoal rot. The broad range of PGP and antifungal activities of the seven SRI isolates demonstrates multiple mechanisms of actions including antibiosis, production of cell wall degrading enzymes and plant growth − promoting hormones indicating its broad spectrum activity. Broad spectrum PGP and biocontrol agents (and their secondary metabolites) offer potentially effective novel strategies for controlling multiple patho- gens and insect pests. A few of the available broad spectrum agents, mostly belonging to Pseudomonas spp., have shown broad spectrum antifungal activity by virtue of volatile and diffusible antibiotics (Hass and Keel 2003; Viji et al. 2003). Bacterial strains from diverse habitats of groundnut with broad spectrum PGP and antifungal activity have been isolated, identified and tested as a seed treatment for the control of collar rot in ground- nut with or without thiram (Kishore et al. 2005). Sec- ondary metabolites of P. aeruginosa possess antifungal, PGP and biocontrol activities (Bano and Musarrat 2003). ICRISAT has identified actinomycetes (isolated from various herbal composts) and bacteria that inhibit Fusarium oxysporum f. sp. ciceri, Rhizoctonia batati- cola, M. phaseolina, Helicoverpa armigera and Spo- doptera litura (Gopalakrishnan et al. 2011b,c,d). The seven broad spectrum potential SRI isolates therefore are likely to be the potential candidates for the discovery of novel secondary metabolites which may be of import- ance for both PGP and biocontrol applications. Competing interests All the authors declare that they have no competing interests. Authors’ contributions SG, HDU, SV, PH, MSV, GA, AS, RV, RKB and MS carried out the physiological traits and field studies, AR done the statistical analysis and SG, SV and OP drafted the manuscript. All authors read and approved the final manuscript. Acknowledgements We thank the Department of Biotechnology, Ministry of Science and Technology, Government of India and the National Bureau of Agriculturally Important Microorganisms for providing financial support. We also thank all the staff of the Biocontrol Unit of ICRISAT including M/s PVS Prasad, P Manohar, B Nagappa, D Barath, A Jabbar and S Rohini for their significant inputs in the laboratory and field studies. Author details 1International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh, India. 2Department of Plant Breeding, CCS Haryana Agricultural University, Hisar 125 004, Haryana, India. Received: 12 October 2012 Accepted: 13 December 2012 Published: 18 December 2012 References Anderson TH, Domsch KH (1989) Ratios of microbial biomass carbon to total organic carbon in arable soils. Soil Biol Biochem 21:471–479 Artursson V, Finlay RD, Jansson JK (2006) Interactions between arbascular mycorrhizal fungi and bacteria and their potential for stimulating plant growth. Environ Microbiol 8(1):1–10 Bano N, Musarrat J (2003) Characterization of a new Pseudomonas aeruginosa strain Nj-15 as a potential biocontrol agent. Cur Microbiol 46:324–328 Basak BB, Biswas DR (2009) Influence of potassium solubilizing microorganisms (Bacillus mucilaginosus) and waste mica on potassium uptake dynamics by sudan grass (Sorghum vulgare Pers.) grown under two Alfisols. Plant Soil 317:235–255 Birkhofer K, Bezemer TM, Bloem J, Bonokowski M, Chritensen S, Dubois D, Ekelund F, Fliessbach A, Gunst L, Hedlund K, Mader P, Mikola J, Robin C, Setala H, Tatin-Froux F, Van der Putten W, Scheu S (2008) Long-term organic farming fosters below and above ground biota; implications for soil quality, biological control and productivity. Soil Biol Biochem 40:2297–2308 Table 5 Effect of SRI isolates on soil chemical activity at harvesting stage of rice cultivation Total nitrogen Available phosphorous Organic Treatment (ppm) (ppm) carbon (%) SRI-156 2015 116 1.52 SRI-158 1967 121 1.48 SRI-178 2134 117 1.57 SRI-211 1930 106 1.61 SRI-229 2027 102 1.61 SRI-305 2072 91 1.51 SRI-360 1961 88 1.56 Control 1926 87 1.47 Mean 2004 103 1.54 SE± 21.3*** 5.8* 0.027* LSD (5%) 71.2 19.3 0.090 CV% 2 8 4 SE = standard error; LSD = least significance difference; CV = coefficient of variance; * = statistically significant at 0.05; *** = statistically significant at 0.001. Gopalakrishnan et al. SpringerPlus 2012, 1:71 Page 6 of 7 http://www.springerplus.com/content/1/1/71 Brooks PC, Landman A, Pruden G, Jenkinson DS (1985) Chloroform fumigation and the release of soil nitrogen; a rapid direct extraction method to measure microbial biomass nitrogen in soil. Soil Biol Biochem 17:837–842 Casida LE (1977) Microbial metabolic activity in soil as measured by dehydrogenase determinations. Appl Environ Microbiol 34:630–636 Cheng Z, Park E, Glick BR (2007) 1-Aminocyclopropane-1-carboxylate deaminase from Pseudomonas putida UW4 facilitates the growth of canola in the presence of salt. Can J Microbiol 53:912–918 Gayathry G (2002) Studies on dynamics of soil microbes in rice rhizosphere with water saving irrigation and in-situ weed incorporation. Ph.D. Thesis submitted to Tamil Nadu Agricultural University, Coimbatore, India Gopalakrishnan S, Humayun P, Kiran BK, Kannan IGK, Vidya MS, Deepthi K, Rupela O (2011a) Evaluation of bacteria isolated from rice rhizosphere for biological control of sorghum caused by M. phaseolina. World J Microbiol Biotechnol 27:1313–1321 Gopalakrishnan S, Kiran BK, Humayun P, Vidya MS, Deepthi K, Rupela O (2011b) Biocontrol of charcoal-rot of sorghum by actinomycetes isolated from herbal vermi-compost. Afr J Biotechnol 10:18142–18152 Gopalakrishnan S, Pande S, Sharma M, Humayun P, Kiran BK, Sandeep D, Vidya MS, Deepthi K, Rupela O (2011c) Evaluation of actinomycete isolates obtained from herbal vermi-compost for biological control of Fusarium wilt of chickpea. Crop Prot 30:1070–1078 Gopalakrishnan S, Ranga Rao GV, Humayun P, Rao VR, Alekhya G, Jacob S, Deepthi K, Vidya MS, Srinivas V, Mamatha L, Rupela O (2011d) Efficacy of botanical extracts and entomopathogens on control of Helicoverpa armigera and Spodoptera litura. Afr J Biotechnol 10:16667–16673 Hao D, Gao P, Liu P, Zhao J, Wang Y, Yang W, Lu Y, Shi T, Zhang X (2011) AC3- 33, a novel secretory protein, inhibits Elk1 transcriptional activity via ERK pathway. Mol Biol Rep 38:1375–1382 Hass D, Keel C (2003) Regulation of antibiotic production in root-colonized Pseudomonas spp. and relevance for biological control of plant disease. Annu Rev Phytopathol 41:117–153 Kishore GK, Pande S, Podile AR (2005) Biological control of collar rot disease with broad spectrum antifungal bacteria associated with groundnut. Can J Microbiol 51:122–132 Lugtenberg BJJ, Dekkers LC (1999) What makes Pseudomonas bacteria rhizosphere competent? Environ Microbiol 1:9–13 Nelson DW, Sommers LE (1982) Total organic carbon and organic matter. In: Page AL, Miller RH, Keeney DR (eds) ‘Methods of soil analysis’, Part 3, Chemical and microbiological properties. Madison, WI, SSSA, pp 539–579 Novozamsky I, Houba VJG, Van ECKR, vanVark W (1983) A novel digestion technique for multiple element analysis. Commun Soil Sci Plant Anal 14:239–249 Olsen SR, Sommers LE (1982) Phosphorus’. In: Page AL (ed) Methods of soil analysis, Agron No. 9, Part 2, chemical and microbial properties, 2nd edn. Am Soc Agron, Madison, WI, USA, pp 403–430 Panhwar QA, Othman R, Rahman ZA, Meon S, Ismail MR (2012) Isolation and characterization of phosphate-solubilizing bacteria from aerobic rice. Afr J Biotechnol 11:2711–2719 Patten C, Glick CR (2002) Role of Pseudomonas putida indol acetic acid in development of host plant root system. Appl Environ Microbiol 68:3795–3801 Penrose DM, Glick BR (2003) Methods for isolating and characterizing ACC deaminase-containing plant growth-promoting rhizo-bacteria. Physiol Plantarum 118:10–15 Soares RA, Roesch LPW, Zanatta G, Camargo FAD, Passaglia LMP (2006) Occurrence and distribution of nitrogen fixing bacterial community associated with oat (Avena sativa) assessed by molecular and microbiological techniques. Appl Soil Ecol 33:221–234 Turner BL, Haygarth PM (2001) Phosphorous solublization in rewetted soils. Nature 411:258 Uren NC (2000) Types, amounts and possible functions of compounds released into the rhizosphere by soil-grown plants. In: Pinto R, Varanini Z, Nannipieri P (eds) The rhizosphere: biochemistry and organic substances at the soil-plant interface. Marcel Dekker, New York, pp 19–40 Uphoff N (2003) Higher yields with fewer external inputs? The system of rice intensification and potential contributions to agricultural sustainability. Int J Agric Sustain 1:38–50 Uphoff N, Anas I, Rupela OP, Thakur AK, Thyagarajan TM (2009) Learning about positive plant-microbial interactions from the system of rice intensification (SRI). Aspect Appl Biol 98:29–54 Viji G, Uddin W, Romaine CP (2003) Suppression of gray leaf spot (blast) of perennial ryegrass turf by Pseudomonas aeruginosa from spent mushroom substrate. Biol Control 26:379–407 Wang Y, Brown HN, Crowley DE, Szaniszlo P (1993) Evidence for direct utilization of a siderophore, ferrioxamine B, in axenically grown cucumber. Plant Cell Environ 16:579–585 doi:10.1186/2193-1801-1-71 Cite this article as: Gopalakrishnan et al.: Plant growth-promoting traits of biocontrol potential bacteria isolated from rice rhizosphere. SpringerPlus 2012 1:71. Submit your manuscript to a  journal and beneﬁ t from: 7 Convenient online submission 7 Rigorous peer review 7 Immediate publication on acceptance 7 Open access: articles freely available online 7 High visibility within the ﬁ eld 7 Retaining the copyright to your article     Submit your next manuscript at 7 springeropen.com Gopalakrishnan et al. SpringerPlus 2012, 1:71 Page 7 of 7 http://www.springerplus.com/content/1/1/71
Title: Plant growth-promoting traits of biocontrol potential bacteria isolated from rice rhizosphere ​
Authors: Subramaniam Gopalakrishnan, HD Upadhyaya, Srinivas Vadlamudi, Pagidi Humayun, Meesala Sree Vidya, Gottumukkala Alekhya, Amit Singh, Rajendran Vijayabharathi, Ratna Kumari Bhimineni, Murali Seema, Abhishek Rathore, Om Rupela
Publisher: SpringerPlus
Date: December 18, 2012 ​
Abstract: Seven isolates of bacteria (SRI-156, SRI-158, SRI-178, SRI-211, SRI-229, SRI-305, and SRI-360) were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum and plant growth promotion (PGP) of the plant. ​ In the present study, the seven isolates were characterized for their physiological traits (tolerance to salinity, pH, temperature, and resistance to antibiotics and fungicides) and further evaluated in the field for their PGP of rice. ​ All the seven isolates were able to grow at pH values between 5 and 13, in NaCl concentrations of up to 8% (except SRI-156 and SRI-360), temperatures between 20 and 40°C, and were resistant to ampicillin (>100 ppm; except SRI-158 and SRI-178) but sensitive (<10 ppm) to chloramphenicol, kanamycin, nalidixic acid, streptomycin (except SRI-156 and SRI-211), and tetracycline. ​ They were tolerant to fungicides benlate and captan, except SRI-158 and SRI-178, bavistin, and sensitive to thiram (except SRI-156 and SRI-211) at field application level. ​ In the field, four of the seven isolates (SRI-158, SRI-211, SRI-229, and SRI-360) significantly enhanced the tiller numbers, stover and grain yields, total dry matter, root length, volume, and dry weight over the un-inoculated control. ​ In the rhizosphere soil at harvest, all the isolates significantly enhanced microbial biomass carbon (except SRI-156), microbial biomass nitrogen, and dehydrogenase activity (up to 33%, 36%, and 39%, respectively) and total N, available P, and % organic carbon (up to 10%, 38%, and 10%, respectively) compared to the control. ​ This investigation further confirms that the SRI isolates have PGP properties. ​