© The Authors, 2026, Published by the Universidad del Zulia*Corresponding author: jsotov@upse.edu.ec
Keywords:
Stenotrophomonas pavanii
Pantoea dispersa
Stomatal density
Zea mays
Pastures
Rhizobacteria
Rhizospheric plant growth-promoting bacteria (PGPR) in corn plants
Bacterias rizosféricas promotoras del crecimiento vegetal (PGPR) en plantas de maíz
Bactérias promotoras do crescimento vegetal rizosférico (PGPR) em plantas de milho
Javier Oswaldo Soto-Valenzuela
1*
Verónica Cristina Andrade-Yucailla
2
Ligia Araceli Solís-Lucas
2
José Humberto Vera-Rodríguez
3
Allison Muyudumbay
1
Anthony Daniel Perero-Perero
1
Rev. Fac. Agron. (LUZ). 2026, 43(1): e264309
ISSN 2477-9407
DOI: https://doi.org/10.47280/RevFacAgron(LUZ).v43.n1.IX
Crop production
Associate editor: Dra. Evelyn Pérez Pérez
University of Zulia, Faculty of Agronomy
Bolivarian Republic of Venezuela
1
Universidad Estatal Península de Santa Elena, Centro
de Investigaciones Biotecnológicas, Santa Elena 240207,
Ecuador.
2
Universidad Estatal Península de Santa Elena, Facultad de
Ciencias Agrarias, Santa Elena 240207, Ecuador.
3
Universidad Agraria del Ecuador, Guayaquil 091307,
Ecuador.
Received: 04-11-2025
Accepted: 04-01-2026
Published: 27-01-2026
Abstract
PGPR are considered a sustainable alternative to improve crop
productivity, for its ability to biostimulate plant growth, induce
systemic resistance, increasing tolerance to abiotic stress, among
other benets. The objective of the study was to evaluate the eect
of plant growth-promoting rhizosphere bacteria (PGPR) on the
germination and development of corn plants. Seven strains obtained
from the Research Center of of the Santa Elena Peninsula State
University, Ecuador, were reactivated, corn seeds were inoculated,
and planted to evaluate germination and plant development in two
stages (laboratory and nursery). The rhizobacteria signicantly
promoted germination by up to 17 %, emergence, and initial
growth of corn, especially the species Stenotrophomonas pavanii
and Pantoea dispersa. In addition, P. dispersa (b) species increased
stomatal density on both leaf surfaces, which could be associated
with better photosynthetic eciency and water use. In conclusion,
S. pavanii and P. dispersa strains promote germination and growth
of Azor corn, the phylogenetic analysis indicates close groupings
with reference isolates for their ecacy with signicant potential
such as (PGPR) with documented biotechnological capabilities for
the genera Pantoea and Stenotrophomonas.
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2-6 |
Resumen
Las PGPR se consideran una alternativa sostenible para mejorar
la productividad de los cultivos, por su capacidad de bioestimular
el crecimiento vegetal, inducir resistencia sistémica, aumentar la
tolerancia al estrés abiótico, entre otros benecios. El objetivo del
estudio consistió en evaluar el efecto de las bacterias rizosféricas
promotoras del crecimiento vegetal (PGPR) sobre la germinación
y el desarrollo de plantas de maíz. Se reactivaron siete cepas
obtenidas del Centro de Investigación de la Universidad Estatal
Península de Santa Elena, Ecuador, se inocularon semillas de maíz
y fueron sembradas para evaluar la germinación y el desarrollo
vegetal en dos etapas (laboratorio y vivero). Las rizobacterias
promovieron signicativamente la germinación hasta un 17 %, la
emergencia y crecimiento inicial del maíz, especialmente las especies
Stenotrophomonas pavanii y Pantoea dispersa. Además, la especie
P. dispersa (b) aumentó la densidad estomática en ambas supercies
foliares, lo que podría estar asociado con una mejor eciencia
fotosintética y un mejor uso del agua. Las cepas S. pavanii y P.
dispersa promovieron la germinación y el crecimiento del maíz Azor,
el análisis logenético indicó agrupaciones cercanas con aislados de
referencia por su ecacia con potencial signicativo como (PGPR)
con capacidades biotecnológicas documentadas para los géneros
Pantoea y Stenotrophomonas.
Palabras clave: Stenotrophomonas pavanii, Pantoea dispersa,
densidad estomática, Zea mays, pastos, rizobacterias.
Resumo
As PGPR são consideradas uma alternativa sustentável para
melhorar a produtividade das culturas, por sua capacidade de
bioestimular o crescimento vegetal, induzir resistência sistêmica,
aumentar a tolerância ao estresse abiótico, entre outros benefícios.
O objetivo do estudo consistiu em avaliar o efeito das bactérias
rizosféricas promotoras do crescimento vegetal (PGPR) sobre a
germinação e o desenvolvimento de plantas de milho. Sete cepas
obtidas do Centro de Pesquisa da Universidade Estadual Península
de Santa Elena, Equador, foram reativadas, inoculadas em sementes
de milho e plantadas para avaliar a germinação e o desenvolvimento
vegetal em duas etapas (laboratório e viveiro). As rizobactérias
promoveram signicativamente a germinação em até 17 %, a
emergência e o crescimento inicial do milho, especialmente as
espécies Stenotrophomonas pavanii e Pantoea dispersa. Além disso,
as espécies P. dispersa (b) aumentaram a densidade estomática em
ambas as superfícies foliares, o que pode estar associado a uma
melhor eciência fotossintética e uso de água. Em conclusão, as cepas
S. pavanii e P. dispersa promovem a germinação e o crescimento do
milho Azor, a análise logenética indica agrupamentos próximos com
isolados de referência por sua ecácia com potencial signicativo,
como (PGPR) com capacidades biotecnológicas documentadas para
os gêneros Pantoea e Stenotrophomonas.
Palavras-chave: Stenotrophomonas pavanii, Pantoea dispersa,
densidade estomática, Zea mays, pastagens, rizobactérias.
Introduction
The use of plant growth-promoting rhizosphere bacteria (PGPR)
is considered a sustainable strategy to improve plant production
(Bhardwaj et al., 2014). These bacterial strains biostimulate plant
development producing several mechanisms that promote it,
such as induced resistance (ISR), and the production of bioactive
compounds (Backer et al., 2018), tolerance to abiotic stress (de
Andrade et al., 2023), improvements in photosynthetic eciency and
antioxidant activity, as well as the bioproduction of siderophores and
exopolysaccharides (Ferrante et al., 2024).
The most commonly reported PGPR microbial strains are genera
of Bacillus, Pseudomonas, and Enterobacter, who’s most investigated
benecial mechanisms include indoleacetic acid production,
solubilize phosphorus and produce siderophores (Posada et al.,
2021). These genera of native bacteria provide signicant benets
to soils for agriculture, acting as natural biocontrol agents protecting
crops from pathogens while promoting plant growth by solubilizing
nutrients and producing plant hormones.
In tropical areas, several native PGPR species such as Pantoea
dispersa and Enterobacter asburiae, rhizosphere isolations of
sugarcane, increased height and weight, the manifestation of defense
genes such as tolerance to extreme pH variations and osmotic
imbalance (Singh et al., 2021). Regarding the use of microbial
associations, studies by Alonazi et al. (2025) highlight positive eects
of ve native genera (Azotobacter, Bacillus, Paenibacillus, Pantoea,
and Pseudomonas), which signicantly increased productivity in
maize plants.
Species such as Stenotrophomonas maltophilia (Upadhyay &
Chauhan, 2022), and Achromobacter piechaudii (Danish et al.,
2020), have been shown to generate high auxin production with
the capacity to form biolms, increase biomass and root growth in
maize crops (Ríos-Ruiz et al., 2024); they also have shown be able
to tolerate high levels of sodium (Peng et al., 2021), and grow well
in soils with extreme pH (Wahab et al., 2024). An increasing number
of rhizobacteria are being reported to be used in the creation of
biocontrol agents and biofertilizers as a biotechnological strategy for
agriculture (Rivera-Hernández et al., 2024).
However, phenotypic expressions induced by PGPR under stress
conditions remain to be investigated, and a faster response would be
the reduction of transpiration after closing their stomata (Bresson et
al., 2013). Zhang et al. (2025) mention that stomata in maize Jingnongke
728 improve photosynthetic carbon assimilation and water eciency,
with a stomatal density ranging of 87.19 stomata.mm
-2
. In this context,
the aim of this study was to assess the inuence of rhizospheric
plant growth-promoting bacteria (PGPR) on maize plants. These
bacteria could have great biotechnological potential in maize
cultivation due to their enhanced biostimulant activity compared to
conventional alternatives, potentially improving crop performance
and development. In this context, the study aimed to evaluate the
eect of plant growth-promoting rhizosphere bacteria (PGPR) on the
germination and development of corn plants
Materials and methods
Bacterial strains and plant material
The bacterial species were obtained and selected for their PGPR
characteristics from the microorganism strain bank of the Centro
de Investigación Biotecnológica (CEB, according its acronyms in
Spanish) of Universidad Estatal Península de Santa Elena, Ecuador,
isolated from grass cultivars (Pennisetum purpureum cv. King Grass
and Panicum maximum cv. Tanzania), as indicated in table 1. The
genotype of seed used for tropical climate corresponded to the Azor
corn hybrid from the Advanta® brand.
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3-6 |
Ten seedlings were randomly evaluated from each replicate per
treatment, in order to measure the height (cm) and stem diameter
(cm).
In situ stage
Sowing, re-inoculation and irrigation
Considering the seedling uniformity, three germinated seeds were
sown per pot and repetition, which contained 1 kilogram of previously
sterilized substrate. At 8 days after transplanting, the second
inoculation was carried out, adding 1 mL of bacterial suspension
(1x10
6
CFU.mL
-1
) on each plant collar (Soto et al., 2016). 15 days after
transplantation (dat), non-viable seedlings were removed from each
experimental unit to preserve the best phenological characteristics,
leaving one plant per pot. Irrigation was carried out every two days
during both phases, to avoid waterlogging. During this stage, the
variables were evaluated:
Measurement of stomatal frequency
A mature leaf was randomly selected from each experimental unit of
the same physiological age to quantify the stomatal frequency on both
sides of the leaves (adaxial and abaxial surface). A cut of the epidermis
was made by taking a 1 cm
2
punch; a grid of the same size was placed
on the 10X objective of the microscope (BOECO
®
, Germany). The
total number of stomata within that square was counted by repeating in
three sectors of each leaf, expressed as stomatal index (SI), under the
formula (Bresson et al., 2013).
Agronomic parameters of maize at 30 days after
transplantation
The variables were evaluated: AL: Aerial length (cm); SD: Stem
diameter (cm); NL: Number of leaves; RL: Root length (cm); AW:
Aerial weight percentage (%); RW: Root weight percentage (%);
AFW: Aerial fresh weight (g); ADW: Aerial dry weight (g); RFW:
Root fresh weight (g); RDW: Root dry weight (g).
Phylogenetic analysis
The identication of the 7 species was carried out, the phylogenetic
analysis based on fragments of the 16S rRNA gene hypervariable
region V4, including 6 strains published as PGPR in corn and alfalfa
crops, of reference sequences from the NCBI GenBank database. For
sequence alignment, ClustalW and BlastN were employed. High-
similarity sequences were selected for subsequent phylogenetic
analysis of the 16S rRNA gene, conducted in MEGA X using the
Neighbor-Joining method. This method provides an optimal balance
of speed and reliability for classifying microorganisms at the genus
and species level. Genetic divergence was calculated based on direct
sequence dierences, and the robustness of the phylogenetic tree was
assessed via a bootstrap analysis with 1,000 replicates.
Statistical analysis
The results were subjected to an analysis of variance (ANOVA)
using the F test at 0.05. The Shapiro-Wilk test was used to assess
normality, and Levene’s test was used to assess homogeneity of
variances. Duncan’s multiple range test was used to assess the
dierential eects between treatments, as it provides greater accuracy
in detecting true dierences with a p-value <0.05. The statistical
software InfoStat version 2020 (Di Rienzo et al., 2020) was used for
data analysis.
Results and discussion
Seed germination percentage
The statistical analysis revealed no signicant dierences among
the treatments, as presented in table 2. However, it is worth mentioning
Table 1. Rhizospheric plant growth-promoting bacteria species
selected for study.
Cultivate Species
Identity
percentage
(%)
Accesion
Tanzania Pantoea dispersa (a) 100.00
KF668475.1
Tanzania Enterobacter asburiae 99.40
MT664184.1
Tanzania Stenotrophomonas pavanii 99.13
PP703128.1
Tanzania Achromobacter xylosoxidans 97.72
NR_113733.1
King grass Pantoea dispersa (b) 100.00
MH675511.1
King grass Stenotrophomonas sp. 100.00
OP389132.1
King grass Stenotrophomonas geniculata 100.00
MT672503.1
Reactivation and growth of bacterial species
The isolates were reactivated in Yeast Mannitol Agar medium
(YMA), by simple streaking and incubated (Memmert, model
BE200, Germany) at 30.5 °C for 48 hours, then transferred to a test
tube with 10 mL of Yeast Mannitol Broth (YMB), placing 1 uL of
colony suspension for each strain and incubated under the same
conditions and under agitation (Boeco, model MSH420, Germany) at
70 revolutions per minute (r.p.m.).
The preparation was centrifuged (THERMO SCIENTIFIC,
MYSPIN6 model, Sweden) at 5.000 rpm for 24 h, where its
absorbance was evaluated in the spectrophotometer (Boeco S-220
UV/VIS, Germany) at 600 nm; using the YMB without inoculating as
a blank, followed by resuspension with distilled water until reaching
a cell population of 1x10
6
UFC.mL
-1
using the Mac Farland scale
(Rayyif et al., 2022).
Experimental design
The study consisted of two stages: (1) in vitro under laboratory
conditions; and (2) in situ under nursery conditions. The experimental
design was a completely randomized design (CRD) consisting of nine
treatments with three replicates in the rst stage. For each treatment,
72 seeds were inoculated, with one germination tray (Gardener’s
Supply Company, 24 wells) constituting an experimental unit. The
treatments were designated as follows: T1 (P. dispersa (a)), T2 (E.
asburiae), T3 (S. pavanii), T4 (A. xylosoxidans), T5 (P. dispersa (b)),
T6 (Stenotrophomonas sp.), T7 (S. geniculata), T8 (distilled water
control), and T9 (gibberellic acid control; NEW GIBERNED
®
from
NEDERAGRO S.A.). In the second stage, 18 germinated seedlings
were chosen from each of the six top-performing treatments, which
included the controls from the in vitro phase.
In vitro stage
Cleansing, disinfection and inoculation of seeds
The seeds were washed with distilled water to remove impurities.
They were then disinfected for three minutes with 5 % sodium
hypochlorite, rinsed with sterile water and nally immersed in 70 %
ethanol for two minutes. A 25 % glucose solution was soaked in the
seeds, then inoculated by immersion using 1.000 mL of the culture
broth at a concentration (1x10
6
CFU.mL
-1
) of each strain according to
the treatments, for 10 minutes (Soto et al., 2016).
The inoculated seeds were placed in germination trays containing
paper towels moistened with sterile distilled water and stored at 28 °C
under constant darkness for seven days. After this rst inoculation,
the germination percentage (GP) of each treatment was evaluated,
using the formula:
GP =
N° of germinates seeds
Total N° of seeds
X 100
SI =
100 x stomatal number
stomatal number + cell number
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4-6 |
averages with 5 leaves present in both cases. However, the variables
root length, percentage of aerial weight, percentage of root weight,
aerial fresh weight, aerial dry weight, root fresh weight and root
dry weight did not show statistical dierences between treatments.
Despite this, the improvement of the averages in those treatments
inoculated with PGPR rhizobacteria is notable.
Table 3. Averages in agronomic parameters of maize cultivation
at 30 days after transplantation.
Treatments
Aerial length
(cm)
Stem diameter
(cm)
Number of
leaves
T1 52.67 ab 6.33 bc 4.33 ab
T3 55.00 ab 8.00 a 5.00 a
T5 60.33 a 6.67 bc 5.00 a
T7 57.33ab 6.67 bc 4.67 ab
T8 55.33 ab 7.67 b 4.67 ab
T9 46.33 b 6.00 c 4.00 b
S.E. 3.49 0.48 0.07
σ 6.04 0.83 0.14
T1 (Pantoea dispersa (a)), T3 (Stenotrophomonas pavanii), T5 (Pantoea dispersa (b)), T7
(Stenotrophomonas geniculata), T8 (distilled water control), T9 (gibberellic acid control).
Data are presented as mean ± standard error (SE) or standard deviation (σ). Within a row,
mean values followed by dierent lowercase letters are not signicantly dierent according to
Duncan’s multiple range test (p>0.05).
The data obtained in this work are consistent with those described
by dierent authors, they conrm that the application of rhizobacteria
biostimulates the development of corn crops (Vera et al., 2025). Thus,
Soto et al. (2016) reports a greater development in aerial length (64.23
cm) at 30 days of cultivation, inoculated with native rhizobia strains.
Pereira et al. (2020) evaluated various inoculation concentrations of
single strains and consortia, which were found to improve biomass
(fresh and dry) in maize under controlled conditions. According to
Bouremani et al. (2023), they mention that the inoculation of plants
with PGPR at early stages promotes root and sprout growth, resulting
in signicant increases in leaf and radical biomass in crops such as
maize.
Stomatal density
The data obtained in the stomatal count submitted to the analysis
of variance; they present statistically signicant dierences between
the treatment being the T5 (P. dispersa (b)) which presented a greater
number of stomata with 77 stomata.cm
2
adaxial and 86 stomas.cm
2
abaxial, for other treatments (Figure 1).
The results obtained in this work agree with what has been
described by dierent authors, who corroborate that the inoculation
of rhizobacteria promotes plant growth and augmentation in maize
cultivation (Vera et al., 2025). Thus, Soto et al. (2016) report greater
development in aerial length (64.23 cm) at 30 days of cultivation,
inoculated with native rhizobia strains. Pereira et al. (2020) also
evaluated dierent inoculation concentrations, single strains and
consortia, and found enhancements in biomass (fresh and dry) in
maize under controlled conditions. According to Bouremani et al.
(2023), inoculation of plants with PGPR at early stages promotes root
and shoot growth, resulting in signicant increases in leaf and root
biomass in crops such as maize.
Several authors such as Bresson et al. (2013) mention that one of
PGPR inoculation eects in maize seedlings was a greater stomatal
control in the closure of stomas to water stress, but without changes
in stomatal density.
that some strains increased the germination percentage of maize seeds
compared to controls by 10 to 17 %. A numerical disparity was presented
in the T3 treatment (S. pavanii), with 86 % of germinated seeds.
Table 2. Eects of PGPR inoculation on germination rate, seedling
diameter and height.
Treatments
Germination
(%)
Seedling diameter
(cm)
Seedling height
(cm)
T1 80 a 2.04 ab
9.67 a
T2 75 a 1.54 d 6.15 bc
T3
86 a 2.18 a 10.40 a
T4 72 a 1.93 b 8.61b
T5 81 a 2.11 ab
10.46 a
T6 64 a 1.67 d 6.41bc
T7 51 a 1.71cd 3.97 c
T8 69 a 2.03 ab
9.87 a
T9 71 a 1.90 bc 7.91 b
S.E. 12.02 0.06 3.03
σ 20.83 0.11 6.91
F 0.77 11.36 7.83
p-value <0.0001 <0.0001 0.0003
gl 26 26 26
T1 (P. dispersa (a)), T2 (E. asburiae), T3 (S. pavanii), T4 (A. xylosoxidans), T5 (P. dispersa
(b)), T6 (Stenotrophomonas sp.), T7 (S. geniculata), T8 (distilled water control), T9
(gibberellic acid control). Values represent mean ± SE or σ. Dierent letters within a column
signify statistically signicant dierences (p<0.05; Duncan’s multiple range test).
The germination-promoting eect of rhizobacteria in various
plant crops may be closely related to the production of phytohormones
(cytokinins, auxins, gibberellines, etc.) information consistent with
what indicated by Noumavo et al. (2013) and Eshaghi Gorgi et al.
(2022) in corn seeds inoculated with species of Enterobacter and
Pantoea genus.
Seedling height and diameter
The results for seedling height and diameter are shown in table
2. The ANOVA and the test of means indicate dierences between
treatments. For seedling diameter, the treatment that showed the best
results was T3 (S. pavanii) at 2.18 cm, regarding seedling height,
treatments T5 (P. dispersa (b)) and T3 (S. pavanii) showed the best
values, with 10.46 and 10.40 cm, respectively.
Soto et al. (2016) in their evaluation regarding the inoculation of
native rhizobacteria in two maize hybrids, showed a higher seedling
height (13.60 cm) in seeds treated with a bacteria/fertilizer consortium.
Amezquita-Aviles et al. (2022) reported that several isolated PGPR
stood out for showing increases of 35-40 % in plant height, in seeds
of Mexican Creole maize. Eshaghi et al. (2024) ndings showed
that PGPR are eective in enhancing maize plant diameter, this type
of bacteria is potentially active. It can increase the availability of
nutrients in the rhizosphere by capturing them (Waday et al., 2022).
Agronomic parameters of maize at 30 days after
transplantation
Table 3 shows the results of a statistical analysis on agronomic
parameters in maize cultivation 30 days after transplantation (dat).
Statistical dierences were observed in the parameters of aerial
length (AL), treatment T5 (P. dispersa (b)) has the highest value and
T9 (Gibberellic acid (Control)) the lowest. In stem diameter (SD), it is
observed that the treatment T3 (S. pavanii) obtained the best average
with 8.00 cm. The parameter number of leaves (NL) indicates that the
treatments T3 (S. pavanii) and T5 (P. dispersa (b)) obtained the best
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Soto-Valenzuela et al. Rev. Fac. Agron. (LUZ). 2026, 43(1): e264309
5-6 |
Figure 1. Stomatal density in maize leaves following inoculation
with plant growth-promoting rhizobacteria (PGPR). T1
(Pantoea dispersa (a)), T3 (Stenotrophomonas pavanii),
T5 (P. dispersa (b)), T7 (S. geniculata), T8 (distilled water
control), T9 (gibberellic acid control). Data are presented
as mean ± standard error. Bars sharing the same lowercase
letter are not signicantly dierent according to Duncan’s
multiple range test (p>0.05).
xation, mineral solubilization, and phytohormone production. While
P. dispersa has the ability to synthesize indoles, produce siderophores
and solubilize phosphates (Amezquita-Aviles et al., 2022). This
agrees with Guevara-López et al. (2025) microbial inoculants cause
an increase in stomatal conductance, which is correlated with the
consumption of intercellular carbon, leading to greater photosynthesis
in the leaves and consequently a greater production of biomass in the
corn crop.
Conclusions
The ndings from both in vitro and in situ germination and
vegetative growth assays demonstrate that the Stenotrophomonas
pavanii and Pantoea dispersa strains, isolated from local agricultural
soils and applied as seed inoculants to Azor hybrid maize, exert a
pronounced biostimulant eect. Compared to the control, these
treatments increased seed germination rates by up to 17 %, plant
height by 6 %, and stem diameter by 7 %. Furthermore, inoculation
with these strains resulted in increased foliar stomatal density-a
PGPR-mediated response that is not widely documented in the
scientic literature.
The robust phylogenetic clustering of these Santa Elena pasture
isolates with eective reference strains, supported by their observed
ecacy, strongly indicates that these native bacterial species hold
signicant promise as plant growth promoters. This nding is
consistent with the documented biotechnological potential of the
Pantoea and Stenotrophomonas genera.
Literature cited
Alonazi, M. A., Alwathnani, H. A., AL-Barakah, F. N. I., & Alotaibi, F. (2025).
Native plant growth-promoting rhizobacteria containing ACC deaminase
promote plant growth and alleviate salinity and heat stress in maize
(Zea mays L.) plants in Saudi Arabia. Plants, 14(7), 1107. https://doi.
org/10.3390/plants14071107
Amezquita-Aviles, C. F., Coronel-Acosta, C. B., Santos-Villalobos, S. D. L.,
Santoyo, G., & Parra-Cota, F. I. (2022). Characterization of native plant
growth-promoting bacteria (PGPB) and their eect on the development
of maize (Zea mays L.). Biotecnia, 24(1), 15-22. https://doi.org/10.18633/
biotecnia.v24i1.1353
Bresson, J., Varoquaux, F., Bontpart, T., Touraine, B., & Vile, D. (2013). The PGPR
strain Phyllobacterium brassicacearum STM196 induces a reproductive
delay and physiological changes that result in improved drought tolerance
in Arabidopsis. New Phytologist, 200(2), 558-569. https://doi:10.1111/
nph.12383
Backer, R., Rokem, J. S., Ilangumaran, G., Lamont, J., Praslickova, D., Ricci,
E., & Smith, D. L. (2018). Plant growth-promoting rhizobacteria:
context, mechanisms of action, and roadmap to commercialization of
Liu et al. (2023), in their study on decient irrigation with
Bacillus pumilus in maize, found that stomatal density was not
aected by inoculation; however, it was inuenced by soil water
status and the PGPR-moisture interaction. This indicates that the
PGPR eect on stomata often depends on the environmental context
(water stress, salinity, etc.). However, Serna (2022), in his work on
stomatal response in maize to climate change, severe water decit
has been reported to decrease stomatal size, aperture, and density,
possibly associated with the need for transpiration cooling in maize
(Yuan et al., 2023). However, this work shows evidence that three of
the six inoculated strains presented higher number of stomata in both
foliar surfaces, with respect to water control; with signicant results
of P. dispersa (b) strain as eect of rhizobacteria, in the increase of
stomatal frequency.
PGPR optimize plant physiology by hormonally regulating
stomatal density, for example, by increasing leaf coverage and
adjusting gas exchange to prevent dehydration. This bacterial
mediation increases enzymatic activity and chlorophyll levels,
thereby enhancing photosynthetic eciency and carbon xation.
Phylogenetic Analysis
Figure 2 shows the 16SrRNA gene sequences of the 7 strains
inoculated in this work, together with the strains P. dispersa AA7
accession no. (MT557017.1), obtained from sugarcane; P. agglomerans
(GQ225111), isolated from corn; P. phytostimulans (PQ300029.1),
isolated from corn; Stenotrophomonas sp. (MT780855.1), isolated
from corn roots; Enterobacter sp. (HM355806) and the E. cloacae
strain (KJ668861.1), isolated from alfalfa crops. Interestingly, a
tiny distance (0.01) is observed between the strains of P. dispersa
(b), S. pavaii and S. geniculata; very close with P. dispersa and
Stenotrophomonas sp., isolated from the rhizosphere of sugarcane
and corn coincidentally reported with very good results in both cases.
The placement of the study strains in the phylogenetic tree alongside
known reference sequences, such as P. dispersa (MT557017.1) and
Stenotrophomonas sp. (MT780855.1), is particularly relevant. These
reference species were isolated from the rhizosphere of important
crops (sugarcane and corn) and have been reported to have very good
results as PGPR (Mareque & Battistoni, 2025; Quach et al., 2025).
Pérez-Pérez et al. (2020) isolated and identied S. pavanii from
the rhizosphere of maize, concluding that this species possesses
characteristics that promote plant growth, biological nitrogen
Figure 2. Phylogenetic tree based on 16S rRNA gene sequences
of the studied plant growth-promoting rhizobacteria
(PGPR) under study (*) and 6 strains published as
PGPR in corn and alfalfa crops.
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2026, 43(1): e264309 January-March ISSN 2477-9409.
6-6 |
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