The Open Agriculture Journal




ISSN: 1874-3315 ― Volume 13, 2019
RESEARCH ARTICLE

Impacts of Microbial Inoculants on the Growth and Yield of Maize Plant



Elizabeth T. Alori1, 2, *, Olubukola O. Babalola2, Claire Prigent-Combaret3
1 Department of Crop and Soil Sciences, Landmark University, Omu-Aran, Nigeria
2 Food Security and Safety Niche Area, Faculty of Natural and Agricultural Sciences, North-West University, 2735 Mmabatho, Mafikeng, South Africa
3 Rhizosphere team, UMR CNRS 5557 Microbial Ecology, Université Lyon, Villeurbanne, France

Abstract

Background:

The use of microbial inoculants holds a great promise to improve crop yield without the negative environmental and health hazard associated with chemical fertilizer.

Aim:

To investigate if Pseudomonas spp. (Pseudomonas kilonensis F113 and Pseudomonas protegens CHA0 strains) have promoting effects on vegetative growth and yield of different maize genotypes (viz. AFLATOXIN SYN 4W, TZB-SR, AFLATOXIN R SYN 2Y, AFLATOXIN SYN 3W and AFLATOXIN SYN-2Y) under different soil types.

Methods:

Both pot and field experiments were employed. Bacterialized seeds were sown (2 seeds/pot/stand).

Results:

Pot experiment showed that both the bacterial species significantly stimulated the growth of maize shoot length, stem girth, leaf length, root length and root weight. The effect of genotypes AFLATOXIN SYN 4W, TZB-SR, AFLATOXIN R SYN 2Y and AFLATOXIN SYN 3W are not significantly different from one another but AFLATOXIN SYN-2Y showed a significantly lower increase in the measured parameters. No significant difference was observed according to soil types. AFLATOXIN SYN 4W showed a significantly higher root weight while AFLATOXIN R SYN 2Y showed a significantly higher root length compared to the other maize genotypes. Moreover, Pseudomonas significantly increased maize growth and yield under field experiment. AFLATOXIN R SYN 2Y and AFLATOXIN SYN 4W showed a significantly higher yield than the other maize genotypes studied.

Conclusion:

We concluded that Pseudomonas kilogenensis F113 and Pseudomonas protegens CHA0 are potential biofertilizers.

Keywords: Biotechnology, Biofertilizers, Maize Gynotype, Microbial Inoculants, Pseudomonas spp., Soil.


Article Information


Identifiers and Pagination:

Year: 2019
Volume: 13
First Page: 1
Last Page: 8
Publisher Id: TOASJ-13-1
DOI: 10.2174/1874331501913010001

Article History:

Received Date: 8/10/2018
Revision Received Date: 24/12/2018
Acceptance Date: 10/1/2019
Electronic publication date: 28/02/2019
Collection year: 2019

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© 2019 Alori et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


* Address correspondence to this author at the Department of Crop and Soil Sciences, Landmark University, Omu-Aran, Nigeria; Tel: +2348063485837; Emails: aloritope@yahoo.com, alori.elizabeth@lmu.edu.ng




1. INTRODUCTION

Maize (Zea mays L.) is a common cereal that is intensively cultivated worldwide [1Alves BM, Filho AC, Toebe M, Burin C, da Silva LP. Variability of grain productivity and energy profile of maize (Zea mays L.) genotypes. J Cereal Sci 2014; 60(1): 164-71.
[http://dx.doi.org/10.1016/j.jcs.2014.02.007]
]. Maize genotypes differ in starch structures and composition of maize kernels (content of amylase and/or amylopectin), grain filling rate, type of endosperm, i.e. floury (dent) vs. horny (flint) and in earliness and rate of maturation [2Ali M, Cone JW, Hendriks WH, Struik PC. Starch degradation in rumen fluid as influenced by genotype, climatic conditions and maturity stage of maize, grown under controlled conditions. Anim Feed Sci Technol 2014; 193: 58-70.
[http://dx.doi.org/10.1016/j.anifeedsci.2014.04.015]
]. Maize genotypes can also differ in a number of plant growth characters [3Aguiar AM, Carlini-Garcia LA, Resende da Silva A, Santos MF, Garcia AAF, Lopes de Souza C Jr. Combining ability of inbred lines of maize and stability of their respective single-crosses. Sci Agric 2003; 60: 83-9.
[http://dx.doi.org/10.1590/S0103-90162003000100013]
] or drought stress resistance ability [4Vacheron J, Combes-Meynet E, Walker V, et al. Expression on roots and contribution to maize phytostimulation of 1-aminocyclopropane-1-decarboxylate deaminase gene acdS in Pseudomonas fluorescens F113. Plant Soil 2016; 407: 187-202.
[http://dx.doi.org/10.1007/s11104-016-2907-0]
].

Numerous agricultural soils worldwide are deficient in plant nutrients. Hence, significant fertilizer requirement is a major challenge for sustainable food production. Previously, these plant nutrients were provided solely in the form of synthetic chemical fertilizers. Such chemical fertilizers are quite expensive and increase crop production cost. In addition, chemical fertilizers lead to soil degradation and pose health hazard to both human and farm animals [5Alori ET, Babalola OO. Microbial inoculant for improving crop quality and human health. Front Microbiol 2018; 9: 2213.
[http://dx.doi.org/10.3389/fmicb.2018.02213] [PMID: 30283427]
]. It is therefore imperative to improve soil fertility, while at the same time preventing associated negative environmental effects of chemical fertilizers.

Microbial inoculants are of growing interest for their potential role in improving soil fertility and enhancing an increase in crop yields and their nutrient contents. Microbial inoculants are the formulations composed of beneficial microorganisms that play important role in every ecosystem. When applied to seeds, soil or seedlings, microbial inoculants improve directly or indirectly the nutrient availability to the host plant and promote plant growth [6Babalola OO, Sanni AI, Odhiambo GD, Torto B. Plant growth-promoting rhizobacteria do not pose any deleterious effect on cowpea and detectable amounts of ethylene are produced. World J Microbiol Biotechnol 2007; 23: 747-52.
[http://dx.doi.org/10.1007/s11274-006-9290-6]
, 7Rokhzadi A, Asgharzadeh A, Darvish F, Nourmohammadi G, Majidi E. Influence of plant growth-promoting rhizobacteria on dry matter accumulation and yield of chickpea (Cicer arietinum L.) under field condition. Amer.-. Euro J Agric Environ Sci 2008; 3(2): 253-7.]. They hold a great promise to improve crop yield (Isfahani and Besharati 2012). In the present agricultural practices, there is a number of beneficiary soil microorganisms used as inoculants. They include Pseudomonassp, Azospirillum, Azotobacter and Phosphobacterium among others [8Babalola OO, Akindolire AM. Identification of native rhizobacteria peculiar to selected food crops in Mmabatho municipality of South Africa. Bio Agric Hort. An Int J Sustain Prod Sys 2011; 27(3-4): 294-309., 9Alori ET, Dare MO, Babalola OO. Microbial inoculants for soil quality and plant health 2017; 281-308.
[http://dx.doi.org/10.1007/978-3-319-48006-0_9]
]. Microbial inoculants improve plant growth through a number of mechanisms which include the production of plant hormones, the supply of nutrients and the suppression of various crop pests [10Toyota K, Watanabe T. Recent trends in microbial inoculants in agriculture. Microbes Environ 2013; 28(4): 403-4.
[http://dx.doi.org/10.1264/jsme2.ME2804rh] [PMID: 24366038]
].

Pseudomonas is a predominant group of rhizosphere soil colonizing bacteria, which have been reported to promote plant growth [11Singh R, Soni SK, Kalra A. Synergy between Glomus fasciculatum and a beneficial Pseudomonas in reducing root diseases and improving yield and forskolin content in Coleus forskohlii Briq. under organic field conditions. Mycorrhiza 2013; 23(1): 35-44.
[http://dx.doi.org/10.1007/s00572-012-0447-x] [PMID: 22648372]
]. Pseudomonas spp. rhizosphere strains have been described as effective phosphate solubilizers [12Igual JM, Valverde A, Cervantes E, Velázquez E. Phosphate-solubilizing bacteria asinoculants for agriculture: Use of updated molecular techniques in their study. Agronomie 2001; 21: 561-8.
[http://dx.doi.org/10.1051/agro:2001145]
]. Verma et al. [13Verma PJ, Yadav J, Tiwari KN. Lavakush, Singh V. Impact of Plant Growth Promoting Rhizobacteria on Crop Production. Int J Agric Res 2010; 5(11): 954-83.
[http://dx.doi.org/10.3923/ijar.2010.954.983]
], noted that Pseudomonas putida strain BHUPSB04 solubilized tricalcium phosphate in soluble form by producing organic acid. Likewise, co-inoculation of Galega orientalis Lam. with root-colonizing Pseudomonas species (Pseudomonas trivialis strain 3Re27 and Pseudomonas extremorientalis strain TSAU20) and Rhizobium, resulted in enhanced root and shoot mass [14Egamberdieva D, Berg G, Lindström K, Räsänen LA. Co-inoculation of Pseudomonas spp. with Rhizobium improves growth and symbiotic performance of fodder galega (Galega orientalis Lam.). Eur J Soil Biol 2010; 46: 269-72.
[http://dx.doi.org/10.1016/j.ejsobi.2010.01.005]
]. However, there have been very little reports on the impact of plant genotypes and soil types on the growth promoting potential of Pseudomonas spp.

In this investigation, we therefore aimed to determine if Pseudomonas spp. (Pseudomonas kilonensis and Pseudomonas protegens strains) have promoting effects on vegetative growth and yield of different maize genotypes under different soil types through the analysis of some indicating factors, such as root length, plant height, root weight and yield of maize plants.

2. MATERIALS AND METHODS

2.1. Plant Material

Seeds of maize cultivars (Aflatoxin SYN 4W, TZB-SR, Aflatoxin R SYN-2Y, Aflatoxin SYN 3W and Aflatoxin SYN-2Y) used in this investigation were obtained from the International Institute of Tropical Agriculture, Ibadan, Nigeria. The seeds were sterilized with 70% ethanol for 2 minutes and washed with sterile distilled water.

2.2. Microbial Inoculant Preparation

P. kilonensis and P. protegens isolates selected for this study were obtained from the Microbial Ecology laboratory (C. Prigent-Combaret). The bacterial isolates were cultured for 48 hrs in Luria-Bertani Broth (LB) medium, and then cells were harvested by centrifugation at 12000g for 10 minutes. Each of the P.kilonensis and P. protegens was suspended in sterile distilled water and the concentration adjusted to give 108cells/ml [15Kumar S, Suyal DC, Dhauni N, Bhoriyal M, Goel R. Relative plant growth promoting potential of Himalayan psychotolerant Pseudomonas jesenii strain MP 1 against native Cicer arietinum (L)., Vigna mungo (L) Hepper; Vigna radiata (L.) Wilczek., Cajanus cajan (L.) Mill.sp and Eleusine coracana (L.) Gaertn. Afr J Microbiol Res 2014; 8(50): 3931-43.].

Ten grams of pectin were suspended in 1 L each of P. kilonensis and P. protegens suspensions, which were shaken for 10 min on a magnetic stirrer plate. Maize seeds were imbibed at the ratio of 500 g/L microbial solutions for 16 hrs.

The bio-inoculated seeds were then air-dried on filter paper for 1 hr before sowing. Another group of surface-sterilized maize seeds (70% ethanol for 2 min) were prepared as control treatments [16El-Mougy NS, Abdel-Kader MM. Long-term activity of bio-priming seed treatment for biological control of faba bean root rot pathogens. Australas Plant Pathol 2008; 37: 464-71.
[http://dx.doi.org/10.1071/AP08043]
].

2.3. Collection of Soil Samples

Soil samples were collected randomly from Mafikeng and Itsoseng areas in South Africa. Mafikeng is located at 25°50'S, 25°38'E. The soil was grey loamy sand with 84% sand, 3% clay and 13% classified as Hutton and Itsoseng is located at 26°08'S, 25°86'E [17Soil classification working group. Classification: A Taxonomic System for South Africa Memoirs of Agric , Natural Resourse of South Africa, Pretoria 1991.]. The soil was red sandy loam with 6.5% silt, 9.8% clay 83.6% sand classified as Ferallic Arenosols [17Soil classification working group. Classification: A Taxonomic System for South Africa Memoirs of Agric , Natural Resourse of South Africa, Pretoria 1991.]. Using the random sampling method, auger samples (5kg) were collected from each sampling units at 0-15 cm. The soil samples collected from each of the sampling sites were bulked and transported to the laboratory in well labelled polyethylene bags. The core samples were then air dried for 3 days and passed through 2 mm sieve in the preparation for analysis.

2.4. Determination of Physical and Chemical Properties of Soil of Study Sites.

The physical and chemical properties measured include: pH using Kent pH metre model 7020, organic matter content using the wet oxidation method as described by [18Shamshuddin J, Jamilah I, Ogunwale JA. Organic carbon determination in acid sulphate soils. Pertanika, J Trop Agric Sci 1994; 17: 197-200.]. The hydrometer method of Gee and Or. was employed in the determination of particle size [19Gee WG, Or D. Particle size analysis Methods of soil Analysis 2002; 253-93.]. Total nitrogen was estimated by the macro Kjeldahl method [20Bremner JM. Total Nitrogen Wisconsin USA1965; 149-1178.1965; ], available phosphorus (P) was determined by Bray-1 extraction method [21Bray RH, Kurtz LT. Determination of total,organic and available forms of phosphorus in soils. Soil Sci 1994; 59: 39-45.
[http://dx.doi.org/10.1097/00010694-194501000-00006]
]. To determine E.C.E.C. the method of Chapman was employed [22Chapman HD. Cation exchange capacityMethods of soil analysis part 2 edn Wisconsin, USA1965; 891-901.]. These are shown in Table 1.

Table 1
Physical and chemical characteristics of the soils.


Table 2
Phenotype characteristics of maize seed used.


2.5. Plant Growth Promotion Studies Under Screen House

A pot experiment was laid in a Randomized Complete Block Design (RCBD) split plot arrangement. The main plot was Pseudomonas spp. (P. kilonensis, P. protegens CHAO and non-inoculated control) applied as seed treatment while the sub plots were maize genotypes (AFLATOXIN SYN 4W, TZB-SR, AFLATOXIN R SYN 2Y, AFLATOXIN SYN 3W and AFLATOXIN SYN-2Y 4W, TZB, AR, 3Wand 2Y) and 2 soil types (Itsoseng soil and Mafikeng soil). Bacterialized seeds were sown (2 seeds/pot) in 35cm-diameter pots filled with 12 Kg of sterilized soil. Soil was wet sterilized in an autoclave at 121ºC for 20 minutes. This is to ensure that only the inoculant introduced influence the sown seed. Only one plant per pot was maintained after germination. All treatments were in triplicates. Plants were irrigated daily at 6.00 hr and 18.00 hr using a watering can. Neither inorganic fertilizer nor pesticide was applied. Physical and chemical properties of the studied soils are shown in Table 1. While the phenotype characteristics of seeds used are recorded in Table 2.

2.6. Growth Parameter Data Collection

Growth parameters (plant height (cm) using a measuring tape, leaf length (cm) using a measuring tape, plant girth (cm) using a thin thread whose length was measured on a ruler, root length (cm) i.e length of the longest root using a measuring tape and root dry weight (g) per plant) were recorded at 12 weeks after planting. To obtain the root dry weight, the below ground portion of the plant was cut and washed to remove attached soil particles. The root was then air dried to a constant weight and the weight was recorded.

2.7. Assessing Plant Growth Promotion of Pseudomonas Spp. Under Field Condition

A field experiment was conducted between September, 2015 and February 2016 at North-West University, Mafikeng, (25°50'S, 25°38'E) South Africa. The Pseudomonas spp. tested were P kilonensis F113 and P protegens CHA0. Maize genotypes used include Aflatoxin SYN 4W, TZB-SR, Aflatoxin R SYN 2Y, Aflatoxin SYN 3W and Aflatoxin SYN-2Y.The soil of the study site was a loamy sand soil, slightly acidic with organic matter value of 1.66%, available phosphorus 1.39PPM, total nitrogen was 0.11 and effective cation exchange capacity was 10.84 (Table 1).

2.8. Experimental Layout

The experimental design was a randomized complete block (RCBD) split plot arrangement with three replications. The main plot was Pseudomonas spp. (P. kilonensisF113, P. protegens CHA0 and non-inoculated control) applied as seed treatment, while the sub plots were maize genotypes (Aflatoxinsyn 4w, TZB-SR, Aflatoxin R SYN 2y, Aflatoxin SYN 3W and Aflatoxin syn-2y). Plot size was 2.2 m2. Interplant and row distance were 50 cm X 50 cm respectively. This gave a plant population of 8 plants per plot which is equivalent to 40,000 plants per hectare. Maize was sown at 3 seeds per hole. This was thinned to two per stand after germination and allowed to grow to maturity. Irrigation was solely by rainfall. Mafikeng had an average annual rainfall of 300 to 700 mm and temperatures range between 22ºC and 34ºC. No fertilizer was applied. Weeding was carried out manually using hoe at 4weeks, 8 weeks and 12 weeks after planting. Pest was controlled by the microbial inoculant. No chemical pesticide was applied. The maize varieties matured at different date however harvesting was carried out same day as maize were left on the stalk in the field to dry.

2.9. Growth Parameter and Yield Data Collection

Growth parameters (plant heights (cm) using a measuring tape, leaf length (cm) using a measuring tape, stem girth (cm) using a thin thread whose length was measured on a ruler were recorded at maturity. Dry maize cobs from each treatment were harvested threshed and the threshed maize seeds were weighed on a weighing scale and recorded as yield (tonnes/ha).

2.10. Statistical Analysis

Data collected from field and pot experiments were subjected to two way Analysis of Variance (ANOVA) using IBM SPSS statistical package 21. Means were compared using Duncan Multiple Range Test (p<0.05).

Table 3
Effects of microbial inoculants, soil types and maize genotype on the growth of maize planted in pots.


3. RESULTS

3.1. Effects of Microbial Inoculants, Soil Types and Maize Genotype on the Growth of Maize Planted in Pots

The results in Table 3 show that plant height, leaf length and plant girth on Itsoseng soil were not significantly different from those on Mafikeng soil. Both P. kilonensisF113 and P. protegens CHAO significantly increased the plant height. P. kilonensis F113 significantly increased plant girth. However, P. protegens CHAO decreased leaf length significantly. Also the growth parameters measurement significantly differed according to maize genotypes (P<0.05).

Combined effect of soil type × maize genotype and microbial inoculant × maize genotype increased significantly the plant height, leaf length and plant girth, while soil type × inoculant × maize genotype significantly increased the plant girth. However, combined effect of soil type × microbial inoculant was not significant on plant height, leaf length and plant girth as reported in Table 3.

Means followed by the same letter along the column for a factor are not significantly different at 5% level of probability using Duncan Multiple Range Test (DMRT).

3.2. Effects of Microbial Inoculants, Soil Types and Maize Genotype on Root Weight and Root Length of Maize Planted in Pots.

The effects of microbial inoculants, maize genotypes and soil type on root weight and root length of maize planted in pot was shown in Table 4. Maize plants inoculated with P. kilonensis F113 significantly increased root weight and root length. Soil from Mafikeng produced a significantly heavier and longer root system than soil from Blaawbank. Maize genotype Aflatoxin SYN 4W produced a significantly higher root weight while maize genotype Aflatoxin R SYN 2Y had a significantly higher root length compared to the other genotypes. Interactions of inoculant × maize genotype, and soil type × inoculant × maize genotypes had significant effect on the both root weight and root length of maize while soil type × inoculant and soil type × maize genotype had significant effect on root length but not on the root weight. Microbial inoculation thus resulted into elongation of stems and roots (Fig. 1).

3.3. Effects of Microbial Inoculants on the Growth and Yield of Maize Planted on the Field

Table 5 shows the effects of Pseudomonas inoculants on the growth and yield of maize planted on the field. Microbial inoculants had very high significant improved effect on growth and yield performance of maize plant. Both P. kilonensis F113 and P. protegens CHA0 significantly increased the plant height, leaf length and the yield of maize (Fig. 2 and Table 5). However, plants inoculated with P. kilonensis F113 had a higher height than those inoculated with P. protegens CHA0. This experiment evidence that the maize genotypes were not significantly different in growth but Aflatoxin SYN 4W and Aflatoxin SYN -2Y produced significantly higher yield followed by TZB SR and Aflatoxin SYN 3W while Aflatoxin R SYN -2Y has the least yield. There was no significant difference between maize genotypes for both growth and yield of maize. Similarly, the effect of maize genotype × inoculant on the growth and yield of maize is not significant. The growth and yield of all the genotypes tested were increased by the inoculants (P=0.05).

Fig. (1)
Effect of microbial inoculant on root of maize. (A) Maize not inoculated with Pseudomonas kilonensis F113 (B) Maize inoculated with a Pseudomonas kilonensis F113.


Table 4
Effects of microbial inoculants, maize genotypes and soil type on root weight and root length of maize planted in pots in Screen house.


Fig. (2)
Biofertilizer effect of microbial inoculant on maizen. (A) Maize (TZB SR) inoculated with pseudomonas kilonensis F113 (B) Maize (TZB SR) not inoculated with a Pseudomonas kilonensis F113.


4. DISCUSSION

The results of this research agree with some other studies where microbial inoculation improved plant growth. Application of microbial inoculants as revealed by Akladious and Abbas caused increase in all measured growth parameters of maize plant [23Akladious SA, Abbas SM. Application of Trichoderma harziunum T22 as a biofertilizer supporting maize growth. Afr J Biotechnol 2012; 11(35): 8672-83.]. Inoculation of maize seeds with P. putida strain R-168, P. fluorescens strain R-93, P. fluorescens DSM 50090, P. putida DSM291 significantly increased plant height in a field experiment [24Gholami A, Shahsavani S, Nezarat S. The Effect of Plant Growth Promoting Rhizobacteria (PGPR) on Germination, Seedling Growth and Yield of Maize. Int J Biol Biomolecular Agric Food Biotechnol Engineer 2009; 3(1): 9-14.]. The growth and yield of maize DMRESRY and EV99-MRP were differentially influenced by the application of bio-fertilizer P. fluorescens [25Diarassouba N, Dago DN, Soro S, Fofana IJ, Silue S, Coulibaly A. Multi-Variant Statistical Analysis Evaluating the Impact of Rhizobacteria (Pseudomonas fluorescens) on Growth and Yield Parameters of Two Varieties of Maize (Zea mays L). Int J Contemporary Appl Sci 2015; 2(7): 206-24.]. According to Oufdou et al. the plant genotype could also influence the phosphorus uptake released by phosphorus solubilizing bacteria from insoluble phosphate [26Oufdou K, Bechtaoui N, El Alaoui A, Benidire L, Daoui K, Göttfert M. Rhizobacteria for Improving of the Agronomic Effectiveness of Phosphate Fertilizers. Procedia Eng 2016; 138: 325-31.
[http://dx.doi.org/10.1016/j.proeng.2016.02.092]
]. P. fluorescens has also shown ability to adapt to survival in soil and colonize the roots of plants [27Kiely PD, Haynes JM, Higgins CH, et al. Exploiting new systems-based strategies to elucidate plant-bacterial interactions in the rhizosphere. Microb Ecol 2006; 51(3): 257-66.
[http://dx.doi.org/10.1007/s00248-006-9019-y] [PMID: 16596439]
] and to protect plant against drought stress [4Vacheron J, Combes-Meynet E, Walker V, et al. Expression on roots and contribution to maize phytostimulation of 1-aminocyclopropane-1-decarboxylate deaminase gene acdS in Pseudomonas fluorescens F113. Plant Soil 2016; 407: 187-202.
[http://dx.doi.org/10.1007/s11104-016-2907-0]
]. Pseudomonas protegens was reported to produce biocontrol compounds [28Ramette A, Frapolli M, Fischer-Le Saux M, et al. Pseudomonas protegens sp. nov., widespread plant-protecting bacteria producing the biocontrol compounds 2,4-diacetylphloroglucinol and pyoluteorin. Syst Appl Microbiol 2011; 34(3): 180-8.
[http://dx.doi.org/10.1016/j.syapm.2010.10.005] [PMID: 21392918]
]. Likewise Stockwell et al. and Yasmin et al. reported biocontrol potential of Pseudomonas spp., against a host of plant disease organisms [29Stockwell VO, Johnson KB, Sugar D, Loper JE. Control of fire blight by Pseudomonas fluorescens A506 and Pantoea vagans C9-1 applied as single strains and mixed inocula. Phytopathology 2010; 100(12): 1330-9.
[http://dx.doi.org/10.1094/PHYTO-03-10-0097] [PMID: 20839963]
,30Yasmin S, Hafeez FY, Rasul G. Evaluation of Pseudomonas aeruginosa Z5 for biocontrol of cotton seedling disease caused by Fusarium oxysporum. Biocontrol Sci Technol 2014; 24(11): 1227-42.
[http://dx.doi.org/10.1080/09583157.2014.932754]
].

Isfahani and Besharati also reported an increase in root weight of cucumber inoculated with Pseudomonas sp. soil type, microbial inoculant, maize genotype have significant positive effect on both root weight and root length of maize [31Isfahani FM, Besharati H. Effect of biofertilizers on yield and yield components of cucumber. J Biol Earth Sci 2012; 2(2): B83-92.].

Table 4 confirms the report by Babalola that microbial activity in the rhizosphere for nutrient acquisition affects root morphology and/or physiology [32Babalola OO. Beneficial bacteria of agricultural importance. Biotechnol Lett 2010; 32(11): 1559-70.
[http://dx.doi.org/10.1007/s10529-010-0347-0] [PMID: 20635120]
]. The stimulation of root growth can enhance plant nutrient uptake [33Alemu F, Alemu T. Pseudomonas fluorescens Isolates Used as a Plant Growth Promoter of Faba Bean (Vicia faba) in vitro as Well as in vivo Study in Ethiopia. Amer J Life Sci 2015; 3(2): 100-8.
[http://dx.doi.org/10.11648/j.ajls.20150302.17]
]. Microbial inoculants often increase plant growth by promoting root development and alter root architecture via the production of phytohormones like Indole-3-Acetic Acid (IAA). This results in increased root length, root surface area numbers of root tips and volume [34Gamalero E, Martinotti MG, Trotta A. Morphogenetic modifications induced by Pseudomonas fluorescens A6RI and Glomus mosseae BEG12 in the root system of tomato differ according to plant growth conditions. New Phytol 2002; 155: 293-300.
[http://dx.doi.org/10.1046/j.1469-8137.2002.00460.x]
,35Vacheron J, Desbrosses G, Bouffaud ML, et al. Plant growth-promoting rhizobacteria and root system functioning. Front Plant Sci 2013; 4: 356.
[http://dx.doi.org/10.3389/fpls.2013.00356] [PMID: 24062756]
]. Such stimulation of roots can aid plant defence against pathogens and can also relate to Induce Systemic Tolerance (IST) [36Ramirez JIS, Maiti RK. Research trends in abiotic stress resistance of crop Springer nature Singapore2016; 131-64.]. Since sites of nutrient uptake include root surfaces and root tips, it is likely that one mechanism by which microbial inoculants lead to increased nutrient uptake is via stimulation of root development [37Yang J, Kloepper JW, Ryu C-M. Rhizosphere bacteria help plants tolerate abiotic stress. Trends Plant Sci 2009; 14(1): 1-4.
[http://dx.doi.org/10.1016/j.tplants.2008.10.004] [PMID: 19056309]
]. A study to investigate effect of P. fluorescens on plant growth promotion under in vitro and in situ conditions conducted by Katiyar and Goel revealed that P. fluorescens produce a significant increase in root (30 and 20%) and shoot length (20 and 24%) of mung bean (Vigna radiata) via phosphorus solubilisation by acid production which results in a decrease in pH [38Katiyar V, Goel R. Solubilization of inorganic phosphate and plant growth promotion by cold tolerant mutants of Pseudo monas fluorescens. Microbiol Res 2003; 158(2): 163-8.
[http://dx.doi.org/10.1078/0944-5013-00188] [PMID: 12906389]
].

Babalola and Glick reported increased plant growth as one of the benefits of microbial inoculants [39Babalola OO, Glick BR. The use of microbial inoculants in African agriculture: Current practice and future prospects J Food Agric Environ 2012; 3&4: 540-49.]. A similar result was reported by Botelho [40Botelho GR, Guimara AV, De Bonis M, Fonseca MEF, Hagler AN, Hagler LCM. Ecology of a plant growth-promoting strain of Pseudomonas fluorescens colonizing the maize endorhizosphere in tropical soil. World J Microbiol Biotechnol 1998; 14: 499-504.
[http://dx.doi.org/10.1023/A:1008867427451]
]. They showed that Pseudomonas fluorescens strain BR-5 stimulated the growth of maize in a natural soil. Microbial inoculants improve plant growth and increase productivity as well as the host plant nutrient status [33Alemu F, Alemu T. Pseudomonas fluorescens Isolates Used as a Plant Growth Promoter of Faba Bean (Vicia faba) in vitro as Well as in vivo Study in Ethiopia. Amer J Life Sci 2015; 3(2): 100-8.
[http://dx.doi.org/10.11648/j.ajls.20150302.17]
].

Table 5
Effects of Pseudomonas inoculants on the growth and yield of maize planted on the field.


Significant difference in plant growth and yield were observed among inoculated and un-inoculated treatments in all the maize genotypes tested. Pseudomonas kilonensis F113 and Pseudomonas protegens CHA0 increased maize plant height, plant girth, and leaf length in both screen house and field experiments with Pseudomonas kilonensis F113 performing the best. The root length and root weight were also enhanced by these organisms in the screen house experiment. Pseudomonas kilonensis F113 also produced the highest yield under field experiment. The impact of microbial inoculants on maize growth and yield were influenced by soil type and crop genotype. Aflatoxin SYN 4W had the best performance. Pseudomonas kilonensis F113 and Pseudomonas protegens CHA0 are potential biofertilizers for maize plants.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

Not applicable.

HUMAN AND ANIMAL RIGHTS

No animals/humans were used for studies that are the basis of this research.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENTS

North-West University is gratefully acknowledged for ETA post- doctoral supports. OOB would like to thank the National Research Foundation, South Africa for grant (Ref: UID81192) that have supported research in her laboratory.

Landmark University Omu-Aran, Nigeria is equally acknowledged for financial support to get this article published.

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