In vitro screening for salinity and drought stress tolerance in plant growth promoting bacterial strains Sarita Kumari 1 Anukool Vaishnav, 1 , Shekhar Jain 1 Devendra Kumar Choudhary, 2, and Kanti Prakash Sharma 1* 1Department of Biosciences, College of Arts, Science & Humanities (CASH), Mody University of Science & Technology, Lakshmangarh-332311, Rajasthan, India

2Amity Institute of Microbial Technology (AIMT), Block ‘E-3’, 4th Floor, Amity University Campus, Sector-125, Noida-201313, Gautam Buddha Nagar, UP, India

*Author to whom correspondence should be addressed; Department of Biosciences, College of Arts, Science & Humanities (CASH), Mody University of Science & Technology, Lakshmangarh-332311, Rajasthan, India/E-Mail: kantipsharma@rediffmail.com

INTRODUCTION

Soil is a largest favorable ecological niche for the microbes and their metabolic activities. Root zone area of plants containing huge

microbial population and high metabolic activities. Instead of the high microbial population and metabolic activities in the rhizospheric area, these microbes occupy only 5% area of the total space (Chakraborty et al., 2015). However, microbial activity or population is not uniform throughout the soil, but is highly concentrated in the region of the root surface area, known as the rhizosphere (Pinton et al., 2001; Chakraborty et al., 2015). Increased populations of microbes colonize the root zone of plants. Microbes present around the plant roots in higher concentration, the main reason of dense microbial population due to presence of higher level of the nutrient availability including amino acid, sugars, organic acids and flavanoids those are execrated from the roots of plants and are then used by the microbes in the soil (Dimkpa et al., 2009; Ashraf et al., 2013). Many literatures are replete with reports describing the plant growth promotion under abiotic stresses in the occurrence of rhizospheric bacteria. Several approaches have been adopted in order to minimize the adverse effect of abiotic stresses including genetically modified crop, but the use of a diverse species of rhizospheric microorganisms containing ACC-deaminase belonging to various taxonomic groups including P s e u d o m o n a s, Azospirillum, Bacillus, Azotobacter, Klebsiella, Enterobacter, Xanthomonas, and S e r a tia , shown to promote plant growth is well known and sustainable approach for enhancing plant tolerance to abiotic stresses including drought, salinity and increases growth (Duan et al., 2009; Yang et al., 2008; Egamberdiyeva, 2009; Tilak et al., , 2005). These microorganisms are generally term as plant growth promoting bacteria (PGPB) are well known for enhancing plant tolerance to abiotic stresses and increases growth (Egamberdiyeva, 2007; Yang e t a l. , 2009; Bharti et al., 2013). PGPB having many plant growth promoting (PGP) traits such as ACC-deaminase, volatiles, antioxidants, Indole-3-acetic acid (IAA) etc. maintain reactive oxygen species (ROS) level in the plants by increasing expression of antioxidant enzymes and maintaining the plant phytohormone levels such as ethylene, ABA, IAA etc. under salt and drought stress (Yang et al., 2009; Choudhary et al., 2012; Vaishnav et al., 2 0 1 3 ; Kumari et al., 2015). This results in induced systemic tolerance (IST). IST is an important process to overcome the harmful effects of abiotic stress such as soil salinity and severe drought stress. PGPB induced physical and chemical responses in plants that result in enhanced tolerance to drought, salinity, heavy metals, cold, heat shock and fertility stresses (Yang et al., 2009). These PGPB have been enhanced the growth of many different crops grown under stressed agriculture land (Dood et al., 2012). The use of PGPB-containing ACC-deaminase to improve plant growth in many crops has been increased worldwide. PGPB contain an enzyme ACC-deaminase lowers the stress ethylene level by conversion of ACC into ammonia and α-ketobutyrate in the plants (root and seed) (Glick 2012). In addition, PGPB possess several other traits like synthesis of auxins, phosphate solubilization, siderophore production etc. which directly promote plant growth (Zahir et al., 2009; Vaishnav et al., 2013; Kumari et al., 2015). Many research studies have been reported the beneficial effect of bacterial inoculum on the plant growth through direct and indirect mechanisms of PGPB under different

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environmental stressed conditions (Khalid et al., 2009; Grover et al., 2011; Glick et al., 2012; Jain et al., 2013; Souza et al., 2015; Choudhary et al., 2015).

Here, the main focus of the present work is to study the tolerance level of PGPB and to check the ACC-deaminase activity and

other plant growth promoting (PGP) activities of selected drought and salt tolerance bacterial strains in the presence of polyethylene glycol (PEG) and NaCl.

MATERIALS AND METHODS

BACTERIAL STRAINS AND ASSESSMENT OF SALT AND DROUGHT STRESS TOLERANCE Nine bacterial strains (CBS-1, CSS-1, CCS-2, CHS-1, CJS-2, CKS-2, Pseudomonas simiae AU, P. koreensis AK-1 and

Carnobacterium sp. SJ-5) were selected for the study.

The salt and drought stress tolerance of selected strains was tested using NaCl and polyethylene glycol (PEG) respectively. The

susceptibility of the selected bacteria in presence of NaCl and PEG was relatively unknown. Take 1 mL of the bacteria-nutrient media suspension added into test-tubes containing 9 mL of nutrient media amended with varying NaCl concentration (0M, 0.2M, 0.4M and

0.6M) for salt stress and PEG concentration (0%, 5%, 10%, and 15%) for drought stress. All test-tubes were kept on shaker at 28± 2 °C for 5 days. Bacteria growth viability under both stresses was monitored over the period of 5 days by measuring the optical density at 600nm.

BIOCHEMICAL ESTIMATION ACC-DEAMINASE AND OTHER PGP TRAITS Measurement of ACC-deaminase and different other plant growth promoting features of bacterial strains was carried out at varying

range of NaCl salt concentration (0M-0.6M) and PEG concentration (0% - 15%).

ACC-DEAMINASE PRODUCTION ASSAY IN BOTH STRESSES

To measure ACC-deaminase activity, bacteria cells were grown in 5 mL of nutrient broth medium at 28ºC for 72 h on orbital

shaker until they reached at stationary phase. To induce ACC-deaminase activity, after the incubation the cells were harvested by the centrifugation, washed twice with 0.1 M Tris-HCl (pH- 7.5), suspended in 4 mL of modified M9 medium supplemented with 5mM ACC concentration, in the presence of NaCl salt concentrations (0M to 0.6M) and PEG concentration (0% to 15%) and incubated at 28ºC for another 48 h on orbital shaker. ACC-deaminase activity was estimated by measuring the amount of α–ketobutyrate generated by the cleavage of ACC (Penrose and Glick 2003).

IAA PRODUCTION ASSAY IN BOTH STRESSES

IAA synthesizing assay in all bacterial strains was measured according to the modified method of Gordon and Weber (1951).

Quantitative estimation of IAA was performed by inoculating 0.2 OD overnight grown culture in 50 mL flask containing 10 mL of nutrient broth amended with 200 Hg/mL of L- tryptophan in the presence of different salt concentrations (0M to 0.6M) and PEG concentration (0% to 15%) at pH 7.0 ± 0.2. L- tryptophan was filter sterilized with 0.22 Hm membrane filter, before adding in nutrient broth.

PHOSPHATE SOLUBILIZATION (Pi-SOLUBILIZATION) ASSAY IN BOTH STRESSES

For quantification determination of Pi-solubilization the method of chlorostannus reduced chloromolybdic acid blue described by

Diby et al., (2005) was used with some modification. A 72 h old bacterial culture of 0.2 OD was inoculated in 50 mL flask containing 10 mL of PVK broth (HiMedia, India) having different salt concentrations (0M to 0.6M) and PEG concentration (0% to 15%) at pH 7.0 ±

0.2 was centrifuged at 8,000 for 15 min at 4°C and the supernatant was used for Pi quantification. The amount of phosphate solubilized by the bacterial cells was calculated using the standard curve of KH 2PO 4.

RESULTS

SURVIVAL RATE OF BACTERIA IN RESPONSE TO NaCl AND PEG

All selected bacterial strains were tested for survival rate in the presence of different NaCl concentration (0M to 0.6M) and PEG

concentration (0%, to 15%). Based on the growth pattern it was shown that the bacterial strains CBS-1, CSS-1, CCS-2, CHS-1, CJS-2 and CKS-2 were able to grow only in 0.2M NaCl concentrations and 5% PEG concentration, whereas bacterial strains AU, AK-1 and SJ-5 were able to tolerate and grow in all NaCl salt and PEG stress conditions (Table 1). On the basis of results of stress tolerance, we have selected three bacterial strains AU, AK-1 and SJ-5 for further characterization of different PGP features.

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Table 1: Effect of varying concentration of NaCl and PEG stress on growth of selected bacterial strains + represents growth of bacterial strain in culture medium after 5 days and – represents no bacterial growth.

BIOCHEMICAL CHARACTERIZATION OF PGP FEATURES UNDER SALT AND PEG STRESSES PGP capabilities of the three selected bacterial strains AU, AK-1 and SJ-5were studied (ACC-deaminase activity, IAA synthesis, Pi-

solubilization, EPS production, siderophore production and proline synthesis) at all NaCl and PEG concentrations. For the biochemical characterization of PGP activities all three strains were grown on the specified medium.

ACC-DEAMINASE ACTIVITY

The ability of all three salt and drought tolerant bacterial strains AU, AK-1 and SJ-5 to utilize ACC as a sole source of N was

determined in the presence of NaCl and PEG concentration. Results of ACC-deaminase activity in the form of α-ketobutyrate formation revealed that all the three strains metabolized ACC in presence or absence of NaCl and PEG (positive for possessing ACC-deaminase activity); whoever under control conditions (without stress), we observed no statistical difference in ACC-deaminase activity of all strains. Activity was decreased with increasing NaCl and PEG concentration. We observed only significant difference at 0.4M NaCl (81 nmol/mg/h) and 10% PEG (73 nmol/mg/h) with strain AU (Fig 1).

Fig 1: Effect of varying concentration of NaCl and PEG on ACC-deaminase activity of AU, AK-1 and SJ-5 bacterial strains. Figure shows P. simiae strain AU is produced more significant different ACC-deaminase activity, 81 nmol/mg/h and 73 nmol/mg/h at 0.4M and 10% PEG respectively. Bars are mean of 3 replicates and error bars show ± standard errors

IAA PRODUCTION

All three bacterial strains were able to produce IAA in control conditions as well as in the presence of NaCl and PEG

concentrations. Bacterial strains produced IAA only in presence of L-tryptophan i.e. tryptophan independent pathway for IAA production was absent in bacterial strains. Upon increasing NaCl and PEG concentration IAA production decreased. All three bacterial strains AU, AK -1and SJ-5 were able to synthesized sufficient IAA production at all NaCl and PEG concentration, whereas we found only significant IAA production value at 0.4M (41.5 Hg/mL) and 10% PEG (39.08 Hg/mL) with P. simiae strain AU respectively (Fig. 2).

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Fig 2: Effect of varying concentration of NaCl and PEG on IAA production of AU, AK-1 and SJ-5 bacterial strains. Figure shows P. simiae strain AU is produced more significant different IAA production, 0.4M (41.5 Hg/mL) and 10% PEG (39.08 Hg/mL). Bars are mean of 3 replicates and error bars show ± standard errors.

QUANTITATIVE ESTIMATION FOR Pi-SOLUBILIZATION

All the selected bacterial strains were checked for inorganic Pi-solubilization in different salt and PEG concentration

quantitatively. All bacterial strains were able to solubilize inorganic phosphate in control and stress condition. The tendency to solubilize Pi decreased as the concentrations of NaCl and PEG increased (Fig. 3). All strains give almost equal quantity of Pi-solubilization. Fig 3: Quantitative Pi-solubilization estimation in all three bacterial strains in different NaCl and PEG concentration and control conditions. Values of bars are mean of 3 replicates and error bars show ± standard errors.

DISCUSSION

ASSESSMENT OF SALT AND DROUGHT TOLERANCE LEVEL

The introduction and perseverance ability of a strain are affected by a many abiotic factors like high salt, severe drought, high pH, and high temperature ( Rojas-Tapias et al., 2012 ). Therefore, tolerance to high salt and water stresses may be important t o identify the most suitable salt and drought tolerant bacteria, containing ACC-deaminase as a biofertilizers for sustainable plant growth under such harsh environmental conditions. Many researchers have been documented the assessment of tolerance level of ACC-deaminase containing bacteria against heavy metal, drought, extreme temperature and different salts, were also characterized for plant growth promotion under extreme environmental conditions (Siddikee et al., 2011; Egamberdieva et al., 2007). It is very likely that microbial species exhibiting their optimum growth and ACC-deaminase activity at extreme environmental conditions might be useful in sites occurring at environmental extremes. In this work, Tolerance of the nine isolated bacteria to salinity and drought stresses has been observed by using different NaCl and PEG concentrations. High salinity and drought stress, by adding varying NaCl and PEG concentrations, resulted in a growth reduction of all strains tested in this investigation. Among the strains, significant reaction differences to both stresses were 63

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obtained. The results tolerance assessment showed that out of nine strains only three strains namely AU, AK-1 and SJ-5 were able to significantly grow in NB supplemented with all NaCl and PEG concentrations at all incubation time. Therefore, the three bacteria could be classified as halotolerant bacteria. Several other studies showed the influence of salinity and drought conditions on the survival of rhizobia in culture medium, using non-permeating substances NaCl and PEG respectively. Naz et al., (2009) also demonstrated that salinity and drought reduced viability of bacterium.

ACC-DEAMINASE AND OTHER PGP ACTIVITIES UNDER NaCl AND PEG CONCENTRATIONS After salt and drought tolerance assay three above selected bacterial strains P. simiae strain AU, P. koreensis strain AK-1 and

Canobacterium sp. strain SJ-5 were further screened for diffent PGP activities under varying concentration of NaCl ranging from 0M to

0.6M and 0 to 15% PEG concentrations.

The role of ACC-deaminase in decreasing stress ethylene level by the enzymatic hydrolysis of ACC into α-ketobutyrate and

ammonia has been presented as one of the critical mechanism of PGPB in promoting plant growth under extreme environmental conditions (Fig. 2). ACC-deaminase activity as measured in all three bacterial strains AU, AK-1 and SJ-5 under NaCl and PEG concentrations, however out off three strains AU showed significant quantity of ACC-deaminase at 0.4M NaCl and 10% PEG concentration (Fig. 1), reflects its ability to utilize ACC as a sole source of nitrogen which can efficiently enhance root length and plant growth under salt and drought stresses. Many researchers have been documented the ACC deaminase containing PGPB improving the salinity and drought tolerance in plants (Siddikee et al., 2011; Nadeem et al., 2009; Nautiyal et al., 2013; Kumari et al., 2015; Singh et al., 2015; Glick et al., 2013; Belimov et al., 2009). Sharp increases in ACC levels and consequently, ethylene synthesis in plants under drought stress conditions have been frequently reported (Arshad et al., 2008). Therefore, the inhibitory effects of ethylene induced by salinity and drought stresses might have been eliminated through ACC-deaminase activity of the PGPR. IAA production is widespread among PGPB and its positive effects on plant growth have been well documented (Spaepen et al.,

2007). Bacterial IAA has been shown to enhance the development of the host plant root system (Patten et al., 2002, Spaepen et al., 2008; Kasotia et al., 2013), which increases the surface area through which soil nutrients are absorbed. Various reports have been published on IAA production by PGPB strains either with or without the tryptophan supplement in culture media, correlated with direct effects on plant growth (Naz et al., 2009). Here, we demonstrate directly that bacterial IAA plays a major role in promotion of root elongation when a bacterium is associated with its host plant under salt and drought stress. In this study, all 3 bacterial isolates able to produce IAA when tryptophan (500ppm) was added in media supplemented with different NaCl and PEG concentrations, however out of them AU isolates was found significantly higher ability to convert tryptophan to IAA than other isolates at 0.4M NaCl and 10% PEG (Fig. 2). When these bacteria inoculated with soybean and mungbean seeds, root length, no. of lateral roots and fresh weight were increased in each individual treatment (Kumari et al., 2015, 2016). Belimov et al., (2015) proposed that rhizobacteria that produce IAA and contain ACC-deaminase decrease amino acid concentrations in the rhizosphere and improve Solanum tuberosum growth and yield under water deficient conditions.

Phosphate solubilizing bacteria (PSB) solubilize inorganic phosphate through directly synthesis of organic acids such as gluconic and citric acid etc. or indirectly solubilize P by decreasing the soil pH, thus converting insoluble phosphate in to soluble form that plants can absorb (Bashan et al., 2013). The unavailability of phosphate to the plants under adverse environmental conditions limits the plant growth, means this element is essential for plant growth. Thus solubilization and mineralization of phosphate by PSB is an important trait of PGPB (Khan et al., 2006; Rodriguz et al., 2004). Here, we were reported the Pi-solubilization of all three strains AU AK-1 and SJ-5 in the Pikovskaya medium supplemented with NaCl and PEG concentrations as well as non-stress (Fig 3). The capacity to solubilize inorganic phosphate is a good characteristic for the selection of bacteria capable of increasing P content in the rhizosphere and their application to increase plant protection against adverse abiotic factors has now been an upcoming strategy (Vassilev et al.,

2012). PSB isolated from canola plants were tested for growth-promoting effects and found able to promote plant growth (Singh et al.,

2014).

CONCLUSION

The findings of the present study are much useful to the agriculture sector for utilizing these potential beneficial bacteria as a bio-inoculant which can successfully improve the stress tolerance and enhance the crop production under salinity and drought stresses. Three bacterial strains belonging to the genera Pseudomonas and Bacillus have been isolated in this study. All three bacterial strains were salt and drought resistance and they can produce high levels of ACC deaminase, IAA and Pi-solubilization. The strain Pseudomonas simiae strain AU showed the possible ability to promote the growth of Vigna radiata under drought stress conditions (Kumari et al., 2016).

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REFERENCES

1. Ashraf MA, Asif M, Zaheer A, Malik A, Ali Q, Rasool M (2013) Plant growth promoting rhizobacteria and sustainable agriculture: A review. Afr J Microbiol Res 7(9):704-709

2. Bashan Y, Kamnev AA, de Bashan LE: A proposal for isolating and testing phosphate-solubilizing bacteria that enhance plant growth. Biol Fertil Soils 2013a, 49: 1-2

3. Belimov AA, Dodd IC, Hontzeas N, Theobald JC, Safronova VI, Davies WJ (2009) Rhizosphere bacteria containing 1-aminocyclopropane-1-carboxylate deaminase increase yield of plants grow in drying soil via both local and systemic hormone signaling. New Phytol 181:413-423

4. Bharti N., Yadav D., Barnawal D., Maji D., Kalra A. (2013) Exiguobacterium oxidotolerans , a halotolerant plant growth promoting rhizobacteria, improves yield and content of secondary metabolites in Bacopa monnieri (L.) Pennell under primary and secondary salt stress. World J. Microbiol. Biotechnol. 29 379–387 10.1007/s11274-012-1192-1

5. Chakraborty U, Chakraborty B, Dey P, Chakraborty AP (2015) Role of microorganisms in alleviation of abiotic stresses for sustainable agriculture. Chakraborty U, Chakraborty B (eds) Abiotic stresses in crop plants. Doi

10.1079/9781780643731.0232

6. Choudhary DK (2012) Microbial rescue to plant under habitat-imposed abiotic and biotic stresses. Appl Microbiol Biotechnol 96:1137–1155

7. Diby P, Sarma YR, Srinivasan V, Anandaraj M (2005) Pseudomonas fluorescens mediated vigour in black pepper ( Piper nigrum L.) under greenhouse cultivation. Ann Microbiol 55(3):171–174

8. Dimkpa CO, Merten D, Svatos A, Buchel G, Kothe E (2009) Metal induced oxidative stress impacting plant growth in contaminated soil is alleviated by microbial siderophores. Soil Biol Biochem 41:154-162

9. Dodd IC, Belimov AA, Sobeih WY, Safronova VI, Grierson D Davies WJ (2005) Will modifying plant ethylene status improve plant productivity in water limited environments? 4th International Crop Science Congress

10. Duan J, Müller KM, Charles TC, Vesely S, Glick BR (2009) 1-Aminocyclopropane-1-carboxylate (ACC) deaminase genes in Rhizobia from southern Saskatchewan. Microb Ecol 57:423–436

11. Egamberdieva D (2009) Alleviation of salt stress by plant growth regulators and IAA producing bacteria in wheat. Acta Physiol Plant 31:861-864

12. Egamberdiyeva D (2007) The effect of plant growth promoting bacteria on growth and nutrient uptake of maize in two different soils. Appl Soil Ecol 36:184–189

13. Glick BR (2012) Plant Growth-Promoting Bacteria: Mechanisms and Applications. Scientifica doi:10.6064/2012/963401

14. Glick BR, Nascimento FX, Vicente CSL, Barbosa P, Espada M et al., (2013) Evidence for the involvement of ACC deaminase from Pseudomonas putida UW4 in the biocontrol of pine wilt disease caused by Bursaphelenchus xylophilus . Biocontrol 58:427–433

15. Gordon SA, Weber RP (1951) Colorimetric Estimation of Indoleacetic Acid. Plant Physiol26(1):192-195

16. Grover M, Ali SkZ, Sandhya V, Rasul A, Venkateswarlu B (2011) Role of microorganisms in adaptation of agriculture crops to abiotic stresses. World J Microbiol Biotechnol 27: 1231–1240

17. Jain S, Vaishnav A, Kasotia A, Kumari S, Gaur RK, Choudhary DK (2013) Bacteria-induced systemic resistance and growth promotion in Glycine max L. Merrill upon challenge inoculation with Fusarium oxysporum . PNAS, India Biol Sci 83: 561-567

18. Kasotia A, Varma A, Choudhary DK (2015) Pseudomonas mediated mitigation of salt stress and growth promotion in Glycine max. Agric Res 4(1):31–41

19. Khan MS, Zaidi A, Wani PA (2006) Role of phosphate-solubilizing microorganisms in sustainable agriculture – a review. Agron Sustain Dev 27:29–43

20. Kumari S, Vaishnav A, Jain S, Varma A, Choudhary D K (2015) Bacterial-mediated induction of systemic tolerance to salinity with expression of stress alleviating enzymes in soybean ( Glycine max L.Merrill).J Plant Growth Regul.10.1007/s00344-015-9490

21. Kumari S, Vaishnav A, Jain S, Varma A, Choudhary D K (2016) Induced drought tolerance through wild and mutant bacterial strain Pseudomonas simiae in mung bean (Vigna radiata L.). World J Microbiol Biotechnol (2016) 32:4

22. Nadeem SM, Zahir ZA, Naveed M, Arshad M (2009) Rhizobacteria containing ACC-deaminase confer salt tolerance in maize grown on salt-affected fields. Can. J. Microbiol 55:1302–1309

23. Nautiyal CS, Srivastava S, Chauhan PS, Seem K, Mishra A, Sopory SK (2013) Plant growth-promoting bacteria Bacillus amyloliquefaciens NBRISN13 modulates gene expression profile of leaf and rhizosphere community in rice during salt stress. Plant Physiol Biochem 66:1–9

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Copyright © 2016 Skyfox Publishing Group

24. Penrose DM, Glick BR (2003) Methods for isolating and characterizing ACC deaminase-containing plant growth-promoting rhizobacteria. Physiol Plant 118:10–5

25. Pinton, R., Varanini, Z., and Nannipieri, P., 2001, The rhizosphere as a site of biochemical interactions among soil components, plants and microorganisms, in: The Rhizosphere. Biochemistry and Organic Substances at the Soil-Plant Interface, Pinton, R., Varanini, Z. and Nannipieri, P., eds., Marcel Dekker, N.Y., pp. 1-17

26. Rodziewicz P, Swarcewicz B, Chmielewska K, Stobiecki M, Wojakowska A (2014) Influence of abiotic stresses on plant proteome and metabolome changes. Acta Physiol Plant 36: 1–19

27. Siddikee MA, Glick BR, Chauhan PS, Yim W, Sa T (2011) Enhancement of growth and salt tolerance of red pepper seedlings ( Capsicum annuum L.) by regulating stress ethylene synthesis with halotolerant bacteria containing 1-aminocyclopropane-1-carboxylic acid deaminase activity. Plant Physiol Biochem 49, 427-434

28. Singh YP, Nayak AK, Sharma DK, Gautam RK, Singh RK, Singh R, Mishra VK, Paris T, Ismail AM (2014) Farmer’s participatory varietal selection: a sustainable crop improvement approach for the 21 st century. Agroecol Sustain Food Syst 38:427–444

29. Singh YP, Mishra VK, Singh S, Sharma DK, Singh D, Singh US, Singh RK, Haefele SM, Ismail AM (2016) Productivity of sodic soils can be enhanced through the use of salt tolerant rice varieties and proper agronomic practices. Field Crop Res 190:82-90

30. Spaepen S, Dobbelaere S, Croonenborghs A, Vanderleyden J (2008) Effects of Azospirillumbrasilense indole-3-acetic acid production on inoculated wheat plants. Plant Soil 312:15–23

31. Spaepen S, Vanderleyden J, Remans R (2007) Indole-3-acetic acid in microbial and microorganism-plant signaling. FEMS Microbiol Rev 31 425–448

32. Tilak KVBR, Ranganayaki N, Pal KK, De R, Saxena AK, Nautiyal CS, Mittal S, Tripathi AK, Johri BN (2005) Diversity of plant growth and soil health supporting bacteria. Curr Sci 89:136-150

33. Vaishnav A, Jain S, Kasotia A, Kumari S, Gaur RK, Choudhary DK (2013) Effect of nitric oxide signaling in bacterial treated soybean plant under salt stress. Arch Microboil 195:571–577

34. Yang J, Kloepper JW, Ryu CM (2009) Rhizosphere bacteria help plants tolerate abiotic stress. Trends Plant Sci 14:1-4

35. Zahir ZA, Ghani U, Naveed M, Nadeem SM, Asghar HN (2009) Comparative effectiveness of Pseudomonas and Serratia sp. containing ACC deaminase for improving growth and yield of wheat ( Triticum aestivum L.) under salt-stressed conditions. Arch Microbiol 191:415–424

CONFLICTS OF INTEREST

“The authors declare no conflict of interest”.

© 2016 by the authors; licensee SKY FOX Publishing Group, Tamilnadu, India. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/) .

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