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Growth-promoting potential of bacterial biomass in the banana micropropagated plants

Potencial da biomassa bacteriana promotora de crescimento no desenvolvimento de mudas micropropagadas de bananeira

ABSTRACT

In the banana production system, a sustainable alternative for producing quality plantlets would be inoculation with plant growth-promoting bacteria (PGPB). Therefore, this study aimed to evaluate the growth-promoting potential of a bacterial biomass in micropropagated banana plantlets cultivar Prata Catarina, and to identify the mechanisms involved in plant-microorganism interactions. In vitro, the biochemical assays tested were the solubilisation of phosphates, production of enzymes, production of ammonia, siderophores, and indole acetic acid. In the in vivo tests, the plants were bacterised (109CFU mL-1) in two phases: acclimatisation, and cultivation in plastic bags. The design was a randomised block with 9 and 7 repetitions per treatment, which were: T1: control; T2: plants treated with isolate E2 (Bacillus pumilus group); T3: plants treated with RAB9 isolate (B. pumilus) for each phase. Bacterial isolates were capable of producing cellulases, amylases, pectinases, lipases, proteases, and siderophores. The plants gained in height, root length, root dry mass, pseudostem diameter, and leaf area. It is concluded that the PGPB can promote the growth of micropropagated banana plantlets through the production of enzymes and siderophores.

Key words:
Bacillus spp.; Musa spp.; plant growth-promoting rhizobacteria

RESUMO

Na bananicultura, uma alternativa sustentável para produção de mudas de qualidade seria a inoculação com as bactérias promotoras de crescimento de plantas (BPCP). Portanto, objetivou-se avaliar o potencial da biomassa bacteriana promotora de crescimento em mudas micropropagadas de bananeira cultivar Prata Catarina e identificar quais os mecanismos envolvidos nas interações planta/microrganismo. As provas bioquímicas testadas in vitro foram solubilização de fosfatos, produção de enzimas, produção de amônia, sideróforos e ácido indolacético. Nos ensaios in vivo, as plantas foram bacterizadas (109UFC mL-1) em duas fases: na aclimatização e no cultivo em sacos plásticos. O delineamento experimental foi em blocos casualizados, com 9 e 7 repetições, por tratamento, dos quais foram: T1: controle; T2: plantas tratadas com isolado E2 (Bacillus pumilus group); T3: plantas tratadas com isolado RAB9 (B. pumilus), para cada uma das fases. Os isolados bacterianos foram capazes de produzir celulases, amilases, pectinases, lipases, proteases e sideróforos. Foram observadas nas mudas ganhos em altura, comprimento da raiz, massa seca da raiz, diâmetro do pseudocaule e área foliar. Conclui-se que as BPCP são capazes de promover o crescimento de mudas micropropagadas de bananeira, através da produção de enzimas e sideróforos.

Palavras-chave:
Bacillus spp.; Musa spp.; rizobactéria promotora de crescimento em planta

Introduction

The banana crop (Musa spp.) has an important socioeconomic role, and the Northeast region of Brazil is the second major producer, contributing 2.233.7 t in 2017 (Agrianual, 2017Agrianual. Disponível em: <http://www.agrianual.com.br/>. Acesso em: Out. 2017..
http://www.agrianual.com.br/...
). In the banana production system, seedlings are produced through micropropagation. A sustainable alternative for the reduction of pesticides and soluble fertilisers in the production of these plants would be inoculation with beneficial microorganisms, such as Plant Growth-Promoting Rhizobacteria (PGPR) (Arturson et al., 2006Arturson, V.; Finlay, R. D.; Jansson, J. K. Interactions between arbuscular mycorrhizal fungi and bacteria and their potential for stimulating plant growth. Environmental Microbiology, v.8, p.1-10, 2006. https://doi.org/10.1111/j.1462-2920.2005.00942.x
https://doi.org/10.1111/j.1462-2920.2005...
; Romeiro, 2007Romeiro, R. S. Controle biológico de enfermidades de plantas: Procedimentos. Viçosa: Editora UFV, 2007. 172p.; Glick, 2012Glick, B. R. Plant growth-promoting bacteria: Mechanisms and applications. Scientifica, v.2012, p.1-15, 2012. https://doi.org/10.6064/2012/963401
https://doi.org/10.6064/2012/963401...
). PGPR promote nutritional growth, antagonism to pathogens, and stimulation of plant host defences (Choudhary & Johri, 2009Choudhary, D. K.; Johri, B. N. Interactions of Bacillus spp. and plants: With special reference to induced systemic resistance (ISR). Microbiological Research, v.164, p.493-513, 2009. https://doi.org/10.1016/j.micres.2008.08.007
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; Hayat et al., 2010Hayat, R.; Ali, S.; Amara, U.; Khalid, R.; Ahmed, I. Soil beneficial bacteria and their role in plant growth promotion: A review. Annual Microbiology, v.60, p.579-598, 2010. https://doi.org/10.1007/s13213-010-0117-1
https://doi.org/10.1007/s13213-010-0117-...
) and several studies have highlighted the growth-promoting activity of these microorganisms in banana plants. The rhizobacteria present positive responses to physiological growth characteristics, as well as to nutritional parameters of banana plants (Baset Mia et al., 2010Baset Mia, M. A.; Shamsuddin, Z. H.; Wahab, Z.; Marziah, M. Rhizobacteria as bioenhancer and biofertilizer for growth and yield of banana (Musa spp. cv. ‘Berangan’). Scientia Horticulturae, v.126, p.80-87, 2010. https://doi.org/10.1016/j.scienta.2010.06.005
https://doi.org/10.1016/j.scienta.2010.0...
; Souza et al., 2016Souza, L. O. D.; Nietsche, S.; Xavier, A. A.; Costa, M. R.; Pereira, M. C. T.; Santos, M. A. Triple combinations with PGPB stimulate plant growth in micropropagated banana plantlets. Applied Soil Ecology, v.103, p.31-35, 2016. https://doi.org/10.1016/j.apsoil.2016.03.001
https://doi.org/10.1016/j.apsoil.2016.03...
).

To promote growth, PGPR use different mechanisms of action such as the production of phytohormones, antibiotics, hydrocyanic acid, lytic enzymes, siderophores, phosphate solubilisation, and nitrogen fixation (Glick, 2012Glick, B. R. Plant growth-promoting bacteria: Mechanisms and applications. Scientifica, v.2012, p.1-15, 2012. https://doi.org/10.6064/2012/963401
https://doi.org/10.6064/2012/963401...
; Souza et al., 2015Souza, R.; Ambrosini, A.; Passaglia, M. P. Plant growth-promoting bacteria as inoculants in agricultural soils. Genetics and Molecular Biology, v.38, p.401-419, 2015. https://doi.org/10.1590/S1415-475738420150053
https://doi.org/10.1590/S1415-4757384201...
). Identification of the compounds produced by the bacteria is fundamental since it permits selection of the most efficient isolates in the colonisation process (Bernardes et al., 2010Bernardes, F. S.; Patrício, F. R. A.; Santos, A. S.; Freitas, S. S. Indução de resistência sistêmica por rizobactérias em cultivos hidropônicos. Summa Phytopathologica, v.36, p.115-121, 2010. https://doi.org/10.1590/S0100-54052010000200002
https://doi.org/10.1590/S0100-5405201000...
). The use of PGPR is an important tool in agricultural production, primarily due to the demand for a decrease in the dependence on soluble fertilisers and defensives within the context of sustainable agriculture (Kumar et al., 2012Kumar, P.; Dubey, R. C.; Maheshwari, D. K. Bacillus strains isolated from rhizosphere showed plant growth promoting and antagonistic activity against phytopathogens. Microbiological Research, v.167, p.493-499, 2012. https://doi.org/10.1016/j.micres.2012.05.002
https://doi.org/10.1016/j.micres.2012.05...
; Ahemad & Kibret, 2014Ahemad, M.; Kibret, M. Mechanisms and applications of plant growth promoting rizobacteria: Current perspective. Journal of King Saud University, v.26, p.1-20, 2014. https://doi.org/10.1016/j.jksus.2013.05.001
https://doi.org/10.1016/j.jksus.2013.05....
).

Therefore, the objective of this study was to evaluate the growth-promoting potential of a bacterial biomass on micropropagated plants of the banana cultivar Prata Catarina, as well as to identify the mechanisms involved in this interaction.

Material and Methods

The experiments were conducted in the year of 2015 in the Laboratories of Post-harvest Pathology, Bioprocess and under greenhouse conditions at Embrapa Agroindústria Tropical (Fortaleza, CE) (3° 45’ 1.4” S, 38° 34’ 30.9” W). The greenhouse had the following climatic variables: minimum and maximum temperatures of 27 and 40 °C, respectively, and 80% mean relative humidity.

The bacterial isolates used were RAB9 (Bacillus pumilus Meyer & Gotttheil) and E2 (Bacillus pumilus group) obtained from the Collection of Cultures of the Laboratory of Phytobacteriology of the Federal Rural University of Pernambuco. The isolates were preserved in NYD broth (dextrose 10 g L-1, yeast extract 5 g L-1, meat extract 3 g L-1 and meat peptone 5 g L-1) with 15% glycerol in an ultrafreezer (-85 °C). For activation, the isolates were transferred to NYDA medium (NYD broth with 18 g L-1 of agar) and incubated at 30 °C in a BOD incubator for 24 h. The bacterial biomass was produced in a 3 L New Brunswick model BioFlo 115 bench, with submerged fermentation and a maximum working volume of 2.2 L, containing 1 L of NYD medium. Rushton impellers with 6 flat blades were used to improve agitation of the reaction medium.

The reactor was fed by filtered compressed dry air at its inlet and outlet through filters (0.20 μm PTFE) and the flow rate used was 6 L min-1. The water for cooling was fed through a Thermo Scientific Chiller System (model Thermo Flex 1400) at 15 °C. After stabilisation of the system, the medium was aseptically inoculated via the septum with a 60 mL syringe fitted with a hypodermic needle containing 50 mL of the inoculum prepared in NYD medium and containing the isolates in the growth logarithmic phase at a concentration of 0.01 g L-1. A further 0.3% of mineral oil was added to prevent foaming. After 24 h of fermentation, the medium was centrifuged at 3500 rpm (Biofuge Stratus, with rotor 15000) for 15 min. The pellets were washed with 30 mL of distilled water and centrifuged again. They were resuspended in distilled water and the concentration of the solution was adjusted to 109CFU mL-1 (according to the McFarland scale). Tween 80 (0.05%) was added to the suspensions to avoid cell aggregation.

For growth promotion, 180 micropropagated plants of the banana cultivar Prata Catarina were used, and were supplied by Bioclone Seedling Production S.A. The plants were removed from flasks, washed, and excessive roots were cut. The plantlets were transferred to expanded 162-cell polystyrene trays containing 5 L of the planting formulation. The formulation consisted of autoclaved soil, dry coconut shell powder, and washed sand (6% HCl solution, for 36 h followed by washing with distilled water until pH = 7) in a ratio of 1:1:1 by volume, and slow-release fertiliser (5 kg m-3) (adapted from Lédo et al., 2008Lédo, A. S.; Oliveira, L. F. M.; Machado, C. A.; Freire, K. C. S. Aclimatação de mudas de bananeira ‘Prata Anã’ regeneradas em diferentes condições de cultivo in vitro. Aracaju: Embrapa Tabuleiros Costeiros, 2008. 18p. Boletim de Pesquisa, 37).

The experiments were conducted in two phases: acclimatisation in trays, and cultivation in 1.5 L plastic bags. In each experiment, the isolates were inoculated by spraying on the aerial part of the plants until the inoculum was completely drained (109 CFU mL-1). In the first experiment, the plants were evaluated 60 days after inoculum spraying in the acclimatisation phase. In the second experiment, the plants were evaluated after 60 days of acclimatisation + 60 days of cultivation in plastic bags.

The variables analysed were plant height (mm), number of leaves, leaf area (cm2), measurement of the length and width of the two largest leaves of the plant, root dry mass (g), diameter of the pseudostem (mm), and length of the root system (mm). For the plants grown in plastic bags, the survival rate was also calculated. The experimental design was in randomised blocks with the following treatments: T1: control, T2: plants treated with isolate E2, and T3: plants treated with RAB9 isolate. For the first and second experiments, 9 replicates (each replicate = one plant) and 7 replicates (each replicate = 4 plants), respectively, were used. The data were submitted to variance analysis and the means were compared by the Tukey test, at 5% probability, using SISVAR software. All data were transformed to √(x + 1).

To characterise the growth-promoting mechanisms of the isolates, the following tests were performed: a) indolacetic acid (AIA) production: King B medium (Romeiro, 2007Romeiro, R. S. Controle biológico de enfermidades de plantas: Procedimentos. Viçosa: Editora UFV, 2007. 172p.) containing tryptophan (5 mM) was used. Ehrlich reagent was added, with the formation of a pink ring being considered positive (adapted from Whitman, 2009Whitman, W. B. Bergey’s manual of systematic bacteriology. 2.ed. Athens: Springer, 2009. 806p.); b) phosphate solubilisation: Mandels and Weber medium (Mandels & Weber, 1969Mandels, M.; Weber, J. The production of cellulases. In: Hajny, G. J.; Reese, E. T. (eds.). Cellulases and their applications. Washington: American Chemical Society, 1969. Chap.23, p.391-414. https://doi.org/10.1021/ba-1969-0095.ch023
https://doi.org/10.1021/ba-1969-0095.ch0...
) rich in calcium phosphate (1%) was used. The formation of a clear zone around the colonies was considered positive (adapted from Cattelan, 1999Cattelan, A. J. Métodos quantitativos para determinação de características bioquímicas e fisiológicas associadas com bactérias promotoras do crescimento vegetal. Londrina: Embrapa Soja, 1999. 36p.); c) production of siderophores: the isolates were grown in King B medium, then centrifuged and Chromium Azurol S (CAS) indicator solution was added to the supernatant. The conversion of the blue color from CAS to yellow indicated production of siderophores (adapted from Cattelan, 1999Cattelan, A. J. Métodos quantitativos para determinação de características bioquímicas e fisiológicas associadas com bactérias promotoras do crescimento vegetal. Londrina: Embrapa Soja, 1999. 36p.); d) ammonia production: a filter paper tape was soaked with an acidity indicator, and the filter tapes were then added to tubes containing the isolates grown in King B medium. Ammonia production was indicated by a pink color in the paper tape (Romeiro, 2007Romeiro, R. S. Controle biológico de enfermidades de plantas: Procedimentos. Viçosa: Editora UFV, 2007. 172p.); e) cellulose utilisation: red congo was added to the isolates grown in Mandels and Weber medium rich in carboxymethylcellulose (CMC). The formation of a clear zone around the colonies was considered positive (Romeiro, 2007Romeiro, R. S. Controle biológico de enfermidades de plantas: Procedimentos. Viçosa: Editora UFV, 2007. 172p.); f) use of chitin: for isolates grown in Mandels and Weber medium rich in chitin, the formation of a light zone around the colonies was considered positive (adapted from Cattelan, 1999Cattelan, A. J. Métodos quantitativos para determinação de características bioquímicas e fisiológicas associadas com bactérias promotoras do crescimento vegetal. Londrina: Embrapa Soja, 1999. 36p.); g) protease production: the isolates were cultured in YMA medium (0.5 g L-1 of K2HPO4, 0.2 g L-1 of MgSO4.7H2O, and yeast extract 0.5 g L-1, pH 7) containing skimmed milk (10%). The formation of a clear zone around the colonies was considered positive (adapted from Souza et al., 2008Souza, H. Q.; Oliveira, L. A.; Andrade, J. S. Seleção de Basidiomycetes da Amazônia para produção de enzimas de interesse biotecnológico. Ciência e Tecnologia de Alimentos, v.28, p.116-124, 2008. https://doi.org/10.1590/S0101-20612008000500019
https://doi.org/10.1590/S0101-2061200800...
); h) use of starch: lugol was added to isolates grown in Mandels and Weber medium rich in soluble starch (1%). The formation of a clear zone around the colonies was considered positive (adapted from Rodrigues, 2006Rodrigues, K. Identificação, produção de antimicrobianos e complexos enzimáticos de isolados de actinomicetos. Porto Alegre: Universidade Federal do Rio Grande do Sul, 2006. 129p. Dissertação Mestrado); i) production of pectinase: red congo was added to the isolates grown in Mandels and Weber medium rich in citrus pectin (1%). The formation of a clear zone around the colonies was considered positive (adapted from Beg et al., 2000Beg, Q. K.; Bhushan, B.; Kapoor, M.; Hoondal, G. S. Production and characterization of thermostable xylanase and pectinase from Streptomyces sp. QG 11-3. Journal of Industrial Microbiology & Biotechnology, v.24, p.396-402, 2000. https://doi.org/10.1038/sj.jim.7000010
https://doi.org/10.1038/sj.jim.7000010...
); j) production of lipase: the isolates were cultured in lipase detection medium (10 g L-1 of peptone, 5 g L-1 of NaCl, 0.1 g L-1 of CaCl2.2H2O, and 18 g L-1 of agar). The presence of halos around the colonies formed by crystals indicated the secretion of lipase (Sierra, 1957Sierra, G. A simple method for the detection of lipolytic activity of micro-organisms and some observations on the influence of the contact between cells and fatty substrates. Antonie van Leeuwenhoek, v.23, p.15–22, 1957. https://doi.org/10.1007/BF02545855
https://doi.org/10.1007/BF02545855...
). All the assays were carried out in triplicate, using the media tested without the addition of bacterial isolates as a control.

Results and Discussion

The biomasses of RAB9 and E2 obtained in the bioreactor were 4.8 and 3.8 g L-1, respectively, in 24 h, under agitation and aeration conditions. The increase in biomass can be attributed to the controlled conditions of pH, temperature, agitation, and aeration of the bioreactor. However, this does not occur when Erlenmeyer flasks are used (Schmidell et al., 2001Schimidell, W.; Lima, U. A.; Aquarone, E.; Borzani, W. Biotecnologia industrial: Engenharia química. São Paulo: Editora Edgard Blucher LTDA, 2001. 554p.).

Regarding aeration, Mantzouridou et al. (2002)Mantzouridou, F.; Roukas, T.; Kotzekidou, P. Effect of the aeration rate and agitation speed on β -carotene production and morphology of Blakeslea trispora in a stirred tank reactor: Mathematical modeling. Biochemical Engineering Journal, v.10, p.123-135, 2002. https://doi.org/10.1016/S1369-703X(01)00166-8
https://doi.org/10.1016/S1369-703X(01)00...
have suggested that it contributes to better microbial development, promoting better homogenisation and oxidation reactions of biomolecules for energy production. Submersed fermentation for large-scale biomass production is considered more adequate due to the ease of control of process parameters (Sousa, 2013Sousa, C. T. de. Produção de biomassa de Bacillus sp. RAB9 por fermentação submersa. Fortaleza: Universidade Federal do Ceará, 2013. 77p. Dissertação Mestrado). Therefore, this type of fermentation was adopted in the above-mentioned study.

After treatments with the bacterial biomass, variation in the development of the micropropagated banana plants was observed both in the acclimatisation and cultivation in plastic bags phases (Figures 1A and B). However, the distinctions in height, leaf area, dry mass, and diameter of the pseudostem were only significantly evident in the culture in bags phase when compared to the control (Tables 1 and 2). In addition, the plants transplanted to bags presented abiotic stress with the presence of burning at the leaf edges, likely due to the high temperatures in the greenhouse. In the plants inoculated with the bacterial isolates, however, a higher survival rate was observed when compared to the uninoculated plants (Table 3).

Figure 1
Micropropagated plantlets of the banana cultivar Prata Catarina treated and untreated with bacterial biomass after 60 days of acclimatisation (A); after acclimatisation and cultivation in plastic bags for 60 days (B)

Table 1
Development of micropropagated plantlets of the banana cultivar Prata Catarina in the acclimatisation phase, after inoculation with the bacterial biomasses (E2 and RAB9)
Table 2
Development of micropropagated plantlets of the banana cultivar Prata Catarina in the cultivation in plastic bags phase, after inoculation with bacterial biomasses (E2 and RAB9)
Table 3
Survival of micropropagated plantlets of the banana cultivar Prata Catarina in the cultivation in plastic bags phase, after inoculation with the bacterial biomasses (E2 and RAB9)

PGPB are known to have significant protection against abiotic stress (Glick, 2012Glick, B. R. Plant growth-promoting bacteria: Mechanisms and applications. Scientifica, v.2012, p.1-15, 2012. https://doi.org/10.6064/2012/963401
https://doi.org/10.6064/2012/963401...
; Vurukonda et al., 2016Vurukonda, S. S. K. P.; Vardharajula, S.; Shrivastava, M.; Skz, A. Enhancement of drought stress tolerance in crops by plant growth promoting rhizobacteria. Microbiological Research, v.184, p.13-24, 2016. https://doi.org/10.1016/j.micres.2015.12.003
https://doi.org/10.1016/j.micres.2015.12...
) and, in the present study, the bacterial isolates used may have conferred protection against adverse factors to the banana cultivar Prata Catarina.

For all the evaluated variables during the cultivation in plastic bags phase, the isolates RAB9 and E2 were prominent in the promotion of growth of the banana plants. The results obtained in the present study are similar to those reported by Mello et al. (2002)Mello, M. R. F.; Mariano, R. L. R.; Menezes, M.; Camara, T. R.; Assis, S. M. P. Seleção de bactérias e métodos de bacterização para promoção de crescimento em mudas de abacaxizeiro micropropagadas. Summa Phytopathologica, v.28, p.222–228, 2002., when a RAB9 isolate was used in micropropagated plants of the pineapple cultivar Pérola. The authors observed increases of 163 and 107% in leaf and root dry matter, respectively, and 87% in leaf area, when compared with uninoculated plants.

The bacterial isolates from the present study presented several mechanisms of action which may be related to the growth promotion seen in the micropropagated plantlets of the banana cultivar Prata Catarina (Table 4).

Table 4
Mechanisms of action of the bacterial isolates RAB9 and E2 for growth promotion of the micropropagated plantlets of the banana cultivar Prata Catarina

However, none of the isolates was able to produce IAA, chitinase, and ammonia, or to solubilise phosphates. Similar results were found by Mello et al. (2002)Mello, M. R. F.; Mariano, R. L. R.; Menezes, M.; Camara, T. R.; Assis, S. M. P. Seleção de bactérias e métodos de bacterização para promoção de crescimento em mudas de abacaxizeiro micropropagadas. Summa Phytopathologica, v.28, p.222–228, 2002. in which none of the isolates presented positive results for the above mentioned biochemical tests. In contrast, in another study, Vardharajula et al. (2011)Vardharajula, S.; Ali, S. Z.; Grover, M.; Reddy, G.; Bandi, V. Drought-tolerant plant growth promoting Bacillus spp.: Effect on growth, osmolytes, and antioxidant status of maize under drought stress. Journal of Plant Interactions, v.6. p.1-14, 2011. https://doi.org/10.1080/17429145.2010.535178
https://doi.org/10.1080/17429145.2010.53...
associated the growth promotion of maize seedlings with isolates of Bacillus sp. that could produce ammonia, indoleacetic acid, and phosphate solubilisers. Therefore, it is likely that other mechanisms are involved in promoting growth in micropropagated plants of the banana cultivar Prata Catarina.

All bacterial isolates from the present study were able to sequester iron and, therefore, were capable of producing siderophores. Ribeiro & Cardoso (2012)Ribeiro, C. M.; Cardoso, E. J. B. N. Isolation, selection and characterization of root-associated growth promoting bacteria in Brazil Pine (Araucaria angustifolia). Microbiological Research, v.167, p.69-78, 2012. https://doi.org/10.1016/j.micres.2011.03.003
https://doi.org/10.1016/j.micres.2011.03...
tested several mechanisms of growth promotion and observed that 37 isolates produced siderophores, including isolates of Bacillus spp.

In terms of the enzymes tested, the RAB9 and E2 isolates could produce amylases (Figures 2A and B), lipases (Figures 2C and D), proteases and pectinases.

Figure 2
Detection of the growth-promoting mechanisms of the bacterial isolates E2 and RAB9. Production of amylases: the presence of a halo lighter than the culture medium (indicated by the arrows) (A-B); Production of lipases: halos formed by crystals (indicated by the arrows) (C-D)

Dinesh et al. (2015)Dinesh, R.; Anandaraj, M.; Kumar, A.; Bini, Y. K.; Subila, K. P.; Aravind, R. Isolation, characterization, and evaluation of multi-trait plant growth promoting rhizobacteria for their growth promoting and disease suppressing effects on ginger. Microbiological Research, v.173, p.34-43, 2015. https://doi.org/10.1016/j.micres.2015.01.014
https://doi.org/10.1016/j.micres.2015.01...
evaluated rhizobacteria associated with ginger rhizosphere in relation to the capacity for growth promotion. All isolates of Bacillus amyloliquefaciens obtained were able to produce proteases, pectinases, cellulases, and α- amylases. In addition, Szilagyi-Zecchin et al. (2014)Szilagyi-Zecchin, V. J.; Ikeda, A. C.; Hungria, M.; Adamoski, D.; Kava-Cordeiro, V.; Glienke, C.; Galli-Terasawa, L. V. Identification and characterization of endophytic bacteria from corn (Zea mays L.) roots with biotechnological potential in agriculture. AMB Express, v.4, p.1-9, 2014. https://doi.org/10.1186/s13568-014-0026-y
https://doi.org/10.1186/s13568-014-0026-...
showed that Bacillus spp. isolates produced pectinases and cellulases, but not chitinase and β 1,3 glucanase.

In the present study, only the RAB9 isolate was able to produce cellulases, by degrading the carboxymethylcellulose (CMC) present in the medium. In another study, Kavamura et al. (2013)Kavamura, V. N.; Santos, S. N.; Silva, J. L.; Parma, M. M.; Ávila, L. A.; Visconti, A.; Zucchi, T. D.; Taketani, R. G.; Andreote, F. D.; Melo, I. S. Screening of Brazilian cacti rizobacteria for plant growth promotion under drought. Microbiological Research, v.168, p.183-191, 2013. https://doi.org/10.1016/j.micres.2012.12.002
https://doi.org/10.1016/j.micres.2012.12...
evaluated the relationship between growth promotion under water stress in native cacti from Caatinga. These authors verified that most of the isolates identified belonged to the genus Bacillus and 79 and 71% of these isolates produced enzyme cellulase and ammonia, respectively, under dry conditions. These results are similar to the results presented in this study since the plants inoculated with the RAB9 isolate (cellulase producer) showed higher survival under greenhouse conditions (temperatures between 27-40 °C).

Our results showed that the use of growth-promoting bacteria inoculated in the phases of acclimatisation and cultivation in plastic bags present a sustainable alternative in the banana production system. The rhizobacteria used in the present study were efficient in promoting the growth of the plants, as evidenced by gains in height, root length and dry weight, pseudostem diameter, and leaf area.

Conclusions

  1. The bacterial biomass promoted increases in the development of the micropropagated banana cultivar Prata Catarina plants.

  2. The mechanisms that may be involved in growth promotion are the production of siderophores and enzymes (proteases, amylases, pectinase, lipases and cellulases).

Acknowledgments

To the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), for research funding. The bio-factory of seedlings Bioclone Produção de Mudas S.A for the supply of banana seedlings used in this work. The authors wish to thank the Plataform of Sequencing LABCEN/CCB in the UFPE for the use of its facilities.

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Publication Dates

  • Publication in this collection
    Nov 2018

History

  • Received
    09 Nov 2017
  • Accepted
    03 July 2018
  • Published
    14 Sept 2018
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