© The Authors, 2021, Published by the Universidad del Zulia*Corresponding author: fcobos@utb.edu.ec
Effects of salinity levels in Oryza sativa in different phenological stages under greenhouse
conditions
Efectos de niveles de salinidad en Oryza sativa en diferentes estados fenológicos en condiciones de
invernadero
Efeitos dos níveis de salinidade em Oryza sativa em diferentes estágios fenológicos em
casa de vegetação
Fernando Cobos Mora
1,2*
Luz Gómez Pando
2
Walter Reyes Borja
1
Edwin Hasang Moran
1
María Ruilova Cueva
1
Perry Lorraine Duran-Canare
3
Rev. Fac. Agron. (LUZ). 2022, 39(1): e223905
ISSN 2477-9407
DOI: https://doi.org/10.47280/RevFacAgron(LUZ).v39.n1.05
Crop Production
Associate editor: Ing. Agr. MSc. Andreina Garcia
1
Universidad Técnica de Babahoyo, Ecuador.
2
Universidad Nacional Agraria, Ecuador.
3
Philippine Rice Research Institute and Central Luzon State
University
Received: 12-02-2021
Accepted: 12-08-2021
Published: 16-12-2021
Abstract
In this research, the agronomic and yield components of rice were
evaluated, subjected to different levels of salinity at different phe-
nological stages. It was made on the greenhouse of the Faculty
of Agricultural Sciences of the Technical University of Babahoyo,
Ecuador. It was established an internally casualized delineation
with an 8 X 3 factorial start with four repetitions, corresponding
to only phenological phases of growth in three doses of salinity
(dS.m
-1
). According to the results obtained, it is concluded that
some agronomic characteristics are affected by high levels of sa-
linity (7.0 dS.m
-1
), showing signicant differences less than 0.05
between the treatments, as in the case of vigor whose level was 7.0
dS. m
-1
. In the same way, chlorophyll levels are signicantly redu-
ced between treatments, being a level of 7.0 dS.m
-1
or more severe.
It is evident that high levels of salinity are detrimental to yield
variations, once at 7.0 dS.m
-1
, or weight of 1000 grains decreased
by 54 %, in quantity or panicle compression by 68 %. Furthermore,
it affects other phenophases such as owering, development and
pickling of its vegetative cycle, mainly in the phases of germina-
tion, molting, prole and growth of caule.
Keywords:
Rice
Phenological stages
Salinity levels
Photosynthesis
Yielding
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2-6 |
Resumen
En esta investigación se evaluó los componentes agronómicos y
de rendimiento en arroz, sometido a diferentes niveles de salinidad en
diferentes etapas fenológicas. Se llevó a cabo en el invernadero de la
Facultad de Ciencias Agrarias de la Universidad Técnica de Babahoyo
en Ecuador. Se estableció un diseño completamente aleatorio con
arreglo factorial 8 X 3 con cuatro repeticiones, correspondiente a
ocho fases fenológicas de crecimiento a tres dosis de salinidad (dS.m
-
1
). De acuerdo con los resultados obtenidos, se concluye que algunas
características agronómicas se ven afectadas por altos niveles de
salinidad (7,0 dS.m
-1
), mostrando diferencias signicativas menor
a 0,05 entre tratamientos, como el caso de vigor cuyo nivel fue de
7,0 dS. m
-1
. De manera similar, los niveles de clorola se reducen
signicativamente entre tratamientos, siendo el nivel 7,0 dS.m
-1
el
más severo. Es evidente, como los altos niveles de salinidad son
perjudiciales para las variables de rendimiento, ya que a 7,0 dS.m
-1
, el
peso de 1000 granos disminuyó en un 54 %, mientras que la longitud
de la panícula en un 68 %. Además, afecta a otras fenofases como la
oración, el desarrollo y acorta su ciclo vegetativo, especialmente en
las fases de germinación, plántula, macollamiento y crecimiento del
tallo.
Palabras clave: Arroz, etapas fenológicas, niveles de salinidad,
invernadero, rendimiento.
Resumo
Nesta pesquisa foram avaliados os componentes agronômicos e de
rendimento do arroz, submetido a diferentes níveis de salinidade em
diferentes estádios fenológicos. Foi realizado na estufa da Faculdade
de Ciências Agrárias da Universidade Técnica de Babahoyo, no
Equador. Estabeleceu-se um delineamento inteiramente casualizado
com arranjo fatorial 8 X 3 com quatro repetições, correspondendo
a oito fases fenológicas de crescimento em três doses de salinidade
(dS.m-1). De acordo com os resultados obtidos, conclui-se que
algumas características agronômicas são afetadas por altos níveis
de salinidade (7,0 dS.m
-1
), apresentando diferenças signicativas
menores que 0,05 entre os tratamentos, como no caso do vigor cujo
nível foi de 7,0 dS. m
-1
. Da mesma forma, os níveis de clorola são
signicativamente reduzidos entre os tratamentos, sendo o nível de
7,0 dS.m
-1
o mais severo. É evidente o quão altos níveis de salinidade
são prejudiciais às variáveis de rendimento, uma vez que a 7,0 dS.m
-1
,
o peso de 1000 grãos diminuiu em 54 %, enquanto o comprimento da
panícula em 68 %. Além disso, afeta outras fenofases como oração,
desenvolvimento e encurta seu ciclo vegetativo, principalmente nas
fases de germinação, muda, perlhamento e crescimento do caule.
Palavras-chave: Arroz, estádios fenológicos, níveis de salinidade,
fotossíntese, produtividade.
Introduction
Rice (Oryza sativa L.) is one of the most important crops in the
world, is produced in 113 countries and is the main food of more than
half of the world’s population, providing 27 % of food energy and 20
% of proteins (FAO, 2018). Not only it is important at the level of food
security, but it represents a substantial source of income for farmers
in Ecuador. In this regard, numerous researches in different areas
including agronomy, pest management and rice genetic improvement
have been developed to increase yields, so that domestic demand can
be met and producers’ protability increased.
In Ecuador the main rice growing provinces are: Guayas with
63.85 % of the growing area, followed by Los Ríos with 28.19 %,
and Manabí with 4.63 %. In some of this area three growing cycles
of rice can be cultivated because favorable environment conditions
(Castro, 2016).
All living organisms are exposed to different types of stress,
which can be caused by man’s activity or natural causes such as air
pollution, drought, temperature, luminous intensity and nutritional
limitations (Rodríguez et al., 2019). Soil salinity is one of the oldest
known problems for agriculture, this problem increases year after
year in arid and semi-arid regions of the world, as a result of low
rainfall and poor management of irrigation water and fertilizers. The
accumulation of soil soluble salts affects the growth, production, yield
and sustainability of many crops (Ramírez et al., 2017). The main
characteristic of saline soils is the presence of high concentrations
of soluble salts, which increases the osmotic potential of the soil
solution, causing physiological stress in the crop, in this type of soil
few plant species can grow and some of them can be unproductive
(Terrazas, 2018).
The salinization of the soils could originate difculties of
plant water absorption, toxicity of specic ions and interference in
physiological processes (indirect effects), reducing the growth and
development of plants (Xiu-wei et al., 2016).
The saline stress can cause slow vegetative development and
subsequently, effects on reproductive development. The primary
consequence of salinity is the reduction in the formation of new
leaves and growth points, this phase is known as the accumulation of
salt at growth points or osmotic phase; the second phase consists of a
slow inhibition of growth, which can take from days to weeks, due to
the accumulation of salts over time, especially in older leaves causing
a premature senescence, this phase is known as the ion phase or salt
toxicity (Roy et al., 2014).
In rice crops with salinization problems, patches of undeveloped
plants are observed in the farmer elds. The plants with salinity stress
can stop growing and have leaves with white tips and chlorosis, and
in turn reduction in stems formation. The symptoms are observed
in the rst leaves then in the second and nally in the developing
leaves. Rice is more tolerant at the germination stage, but they can be
affected during the transplanting period, in the owering stage with
sterility peaks which number can be increased reducing the weight
and grains, affecting the yields (Dobermann and Fairhurst, 2012).
In Ecuador, the Guayas River Basin, which accounts for 40.4 % of
the country’s irrigable area, has abundant water with a ow of 8,847
m
3
.year
-1
; however, in the soils of the basin there is accumulation of
salts. The salinity conditions are due to the saline intrusion in this
area of the Babahoyo River, which enters through the estuaries and
irrigation channels. The problems of salt in the soils are increased by
poor drainage (Pozo et al., 2010).
This work aims to identifying the phenological stage and the
salinity level in which the rice crop is most affected by saline stress,
measured in agronomic components and yield.
Materials and methods
This research was conducted in the greenhouse of the Faculty
of Agricultural Sciences of the Technical University of Babahoyo,
located in Babahoyo, Los Ríos province, Ecuador, geographically
located at 79°32´ W longitude and 01°49´ S latitude, elevation
of 8 m.a.s.l., temperature of 30.4 °C, relative humidity 65.5 %
(greenhouse), evaporation 1012.4 mm, heliophany 830.4 hours
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Cobos et al. Rev. Fac. Agron. (LUZ). 2022, 39(1): e223905
3-6 |
(INAMHI, 2019). The rice variety used in this study was INIAP 14,
with early life cycle and moderately susceptible to salinity. It is an
indica type rice, with long-grained variety, growing in signicant
percentage of Ecuador’s rice area.
Factor A corresponds to eigth phenological growth phases of rice,
as mentioned below: germination (1), seedling (2), tillering (3), stem
growth (4), oral primordia (5), booting (6), owering (7) and milky
grain stage (8); factor B corresponds to saline treatments,: normal
water or control 0.2 dS.m
-1
(1), mean salinity level of 3.5 dS.m
-1
(2)
and high salinity level of 7.0 dS/m
-1
(3) measured through electrical
conductivity (EC), expressed in deciSiemens per meter (dS.m
-1
)
(critical salinity levels referred by Cedeño, 2015). It should be noted
that the water salinization with the doses of 3.5 and 7.0 dS.m
-1
were
made at the beginning of each phenological phase in study and
maintained until harvesting of plants.
The experiment was established under a Completely Random
Design (DCA) using a factorial arrangement 8 X 3 with four
repetitions. The evaluated variables were subjected to the variance
analysis and the Tukey test (p> 0.05), to determine statistical
differences between treatment means.
In the greenhouse, a hydroponic system was conditioned using
wooden boxes with the dimensions of 60 cm wide and 80 cm long,
covered with black polyethylene for the establishment of rice plants.
Pumice stone was used as an inert substrate, which was homogenized
and washed. Two seeds were sown per site (6 sites/box) to allow the
establishment of the experimental unit, after germination of the seeds,
one of the seedlings was removed to nally leave six plants per box.
Irrigations were applied twice a week during the rst two months of
cultivation and then watered weekly until the end of the experiment.
In order to achieve salinity levels in the treatments described above,
water was supplied with the salt content or electrical conductivity
(EC) dened in the treatments, which was salinized with sodium
chloride (NaCl), because this salt is predominantly in saline soils
and has the highest toxicity. These values were measured with the
Bluelab combined conductivity meter (Bluelab Corporation Limited,
Tauranga 3110, New Zealand).
The following variables were measured: Vigor (scale of CIAT’s
standard evaluation system for rice (Jennings et al., 1981), plant
height (cm), tillers per plant, root length (cm), owering (days),
vegetative cycle (days), panicle length (cm), grains per panicle,
panicles per plant, panicle sterility ( %), weight of 1000 grains (g),
grain weight per panicle (g), degree ( %), length and width of the
ag leaf (cm), length and width of the second leaf (cm), length and
width of the husked grain (mm), length and width of shelled grain
(mm), grain shape, fresh and dried root biomass (g), fresh and dry
biomass of the aerial part (g), chlorophyll content ( %) measured by
an chlorophyll meter at Leaf® brand, model CHL PLUS.
Results and discussion
Regarding to the variable vigor, the phenological stages of oral
primordia, booting, owering and milky grain stage formation,
presented the highest vigor with a mean of 3, being statistically
superior (<0.0001) to the rest of treatments (gure 1). The salinity
level of 0.2 dS.m
-1
with a mean of 1, was statistically higher (<0.0001)
than the other treatments, with the treatment 7.0 dS.m
-1
being the most
affected with a mean of 6.13, corresponding to less vigorous plants
than normal, according on the used scale.
Figure 1. Variation in the vigor of rice plants through 8
phenological phases subject to different salinity levels.
The interactions of the phenological stages of germination,
seedling, tillering, stem growth, oral primordia, booting, owering
and milky grain stage with the salinity level of 0.2 dS.m
-1
(control); do
not differ statistically (<0.0001) from each other and are superior to
other interactions. The phenological stages of germination, seedling,
tillering and stem growth with the salinity level of 7.0 dS.m
-1
, had
vigor’s a mean of 7 and 8, corresponding to a very weak and small
plants, according to the used scale. Figure 1 shows the variation in
vigor presented by plants through the eight phenological phases
subject to salinity levels of 3.5 and 7.0 dS.m
-1
.
The phenological phases, such as the milky grain stage, owering,
booting and oral primordia, were those that exhibited less sterility;
these are 10.32, 12.04, 12.82 and 14.15 %, respectively; and have
similar statistical signicance (<0.0001). The remaining phenological
stages had higher mean values for this variable. The lowest sterility
(<0.0001) was found at the 0.2 dS.m
-1
level equal 10.06 %.
As for the interactions of the phenological phases of germination,
seedling, tillering, stem growth, oral primordia, booting, owering
and milky grain stage with the salinity level of 0.2 dS.m
-1
(control),
presented statistically similarity (<0.0001); likewise, the oral
primordia, booting and owering phase with salinity of 3.5 dS.m
-1
and oral primordia, booting and owering with 7.0 dS.m
-1
. The
remaining interactions showed higher percentage of panicle sterility.
Figure 2 shows the variation in panicle sterility obtained with salinity
levels of 3.5 and 7.0 dS.m
-1
.
Figure 2. Variation of panicle sterility obtained with salinity levels
of 0.2, 3.5 and 7.0 dS.m-1.
About plant height, the phenological stages of owering, milky
grain stage, booting and owering, had the higher plant height with
mean of 68.92, 69.15, 70 and 69.33 cm, respectively, statistically
superior (<0.0001) to other treatments. The mean of 75.75 cm with
the salinity level of 0.2 dS.m
-1
(control) was statistically higher
(<0.0001) to other treatments.
The interactions of the phenological stages of germination,
seedling, tillering, stem growth, oral primordia, booting, owering
Germination Seedling Tillering
Stem
growth
Floral
primordia
Booting
stage
Flowering Milky state
0.2 dS / m
10.06 10.06 10.06 10.06 10.06 10.06 10.06 10.06
% 3.5 dS / m
26.33 25.50 21.08 19.02 14.66 12.12 11.76 10.34
% 7.0 dS / m
58.74 54.59 37.36 24.22 17.74 16.27 14.28 10.55
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
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Rev. Fac. Agron. (LUZ). 2022, 39(1): e223905. January - March. ISSN 2477-9407.
4-6 |
and milky grain stage, with the salinity level of 0.2 dS.m
-1
; were
statistically similar (<0.0001), but superior to the rest of the
interactions. The phenological stages of germination, seedling,
tillering and stem growth, with the salinity level of 7.0 dS.m
-1
;
they had the lower plant height mean equal to 23.1, 35.75, 37.55
and 48.39 cm, respectively. The fact that the height of the plant
decreased as NaCl concentrations increased, is due to the fact that
salts affect growth altering the absorption of water by the roots,
a phenomenon that is called the osmotic component according to
López et al., (2018). In saline environments, the reduction in the
height of the seedlings due to the inhibitory effect of sodium, is a
common phenomenon of several species, including rice (Abbas et
al., 2013; Rajakumar, 2013). Similar results found Batista et al.,
(2017) in bail (Ocimum basilicum L) seedlings that decreased in
height as NaCl levels increased.
Figure 3 shows negative values representing percentage values
that were decreased by salinity at 3.5 and 7.0 dS.m
-1
levels compared
to the control with 0.2 dS.m
-1
. For the variable number of tillers
per plant, the phenological stages of milky grain stage, booting and
owering had the higher mean of tillers with values of 19.15, 18.87
and 18.72, respectively, statistically superior (<0.0001) to the other
treatments. The salinity level of 0.2 dS.m
-1
with a mean of 20.83,
was statistically (<0.0001) higher than other treatments, while the
lower value was achieved by the salinity level of 7.0 dS.m
-1
, with
13.93 tillers.
Figure 3. Variation of the variable panicle length with salinity
levels of 0.2, 3.5 and 7.0 dS.m
-1
.
In relation to the interactions of the phenological stages of
germination, seedling, tillering, stem growth, oral primordia,
booting, owering and milky grain stage with the salinity level of
0.2 dS.m
-1
and oral primordia, booting, owering, milky grain
stage, with the salinity of 3.5 dS.m
-1
; were statistically similar
to each other (<0.0001), but superior to other interactions. The
phenological stages of germination, seedling, tillering, stem growth
and oral primordia, with the salinity level of 7.0 dS.m
-1
; had the
lowest means with 10.25, 11.25, 12.89, 13.31 and 13.65 tillers,
respectively. Nawaz et al., (2010), indicate that damages are the
result of disorders caused in the metabolism of plants, mainly
due to changes in the osmotic potential of the soil, the nutritional
imbalance due to interaction between toxic ions and nutrients
essential for growth and development.
In the variable panicle length, the Tukey test (p> 0.05),
determined that the phenological stages of the milky grain stage,
owering, booting, oral primordia, stem growth and tillering,
had similar statistical signicances (<0.0001), reaching the longer
panicle length with 23.7, 22.99, 22.75, 22.64, 22.39 and 21.89 cm,
respectively. The salinity level of 0.2 dS.m
-1
with a mean of 25.43
cm was statistically higher (<0.0001) than other treatments.
Referring to the interactions of the phenological stages of
germination, seedling, tillering, stem growth, oral primordia,
booting, owering and milky grain stage, with the salinity level
of 0.2 dS.m
-1
and the seedling stages, tillering, stem growth, oral
primordia and booting with the salinity of 3.5 dS.m
-1
; they do not
differ statistically (<0.0001) and are superior to other interactions.
The phenological stages of germination and seedling, with the
salinity level of 7.0 dS.m
-1
, had lower mean with values of 8.03 and
8.02 cm. The results of this study coincide with Martinez (2002),
who mentions that salinity causes morphological damage in plants
such as a decrease in leaf size to lower transpiration, reduction of the
number of nerves and stomata. Finally, it affects the phenological
level, causing a delay in owering.
The phenological stages of the milky grain stage, owering,
booting, owering primordia and stem growth had the highest
amount of grains per panicle with means of 128.51, 126.93, 125.32,
123.28 and 120.24 grains, respectively; being statistically superior
(<0.0001) to other treatments. The salinity level of 0.2 dS.m
-1
with
an average of 140.33 grains per panicle was higher (<0.0001) than
other treatments, the treatment with 7.0 dS.m
-1
, shown the lowest
value with 89.89 grains.
With regard to the interactions of the phenological stages of
germination, seedling, tillering, stem growth, oral primordia,
booting, owering and milky grain stage with the salinity level
of 0.2 dS.m
-1
and the stages of stem growth, oral primordia,
owering and milky grain stage with salinity of 3.5 dS.m
-1
, were
statistically similar (<0.0001), but superior to other interactions.
The phenological stages of germination and seedling, at the salinity
level of 7.0 dS.m
-1
, obtained the lower values of 55.1 and 63.76
grains, respectively. The results presented support the observations
of other authors that increasing salinity reduces development and
affects rice yield in its different growth stages (Lutts et al., 1995).
For the variable grains weight per panicle (gure 4), the
phenological stages of milky grain stage, owering and oral
primordia had the higher grain weight values, with means of 1.67,
1.61 and 1.56 g, respectively; statistically superior (<0.0001) to
other treatments. The salinity level of 0.2 dS.m
-1
with a mean of
1.78 g, was statistically higher (<0.0001) than other treatments. The
salinity of 7.0 dS.m
-1
shown the lowest value with 1.27g.
Figure 4. Variation of the variable grain weight per panicle (g)
with the effect of salinity levels of 0.2, 3.5 and 7.0
dS.m
-1
.
The interaction of the phenological stages of germination,
seedling, tillering, stem growth, oral primordia, booting, owering
and milky grain stage with salinity level of 0.2 dS.m
-1
, the interaction
of stem growth, oral primordia and milky grain stage with salinity
level of 3.5 dS.m
-1
and the interaction of milky grain stage with the
salinity level of 7.0 dS.m
-1
, were statistically similar (<0.0001), but
superior to other interactions.
The phenological stages of germination and seedling at the
salinity level of 7.0 dS.m
-1
; presented the lowest average with 0.84
Germination Seedling Tillering Stem growth
Floral
primordia
Booting Flowering
Milky stage
grain
0.2 dS / m
25.43 25.43 25.43 25.43 25.43 25.43 25.43 25.43
3.5 dS / m
19.69 22.26 22.08 22.88 23.03 23.39 23.85 25.71
7.0 dS / m
8.03 8.02 18.17 18.85 19.46 19.44 19.68 19.95
0.00
5.00
10.00
15.00
20.00
25.00
30.00
Germination Seedling Tillering Stem growth
Floral
primordia
Booting Flowering
Milky stage
grain
0.2 dS / m
1.78 1.78 1.78 1.78 1.78 1.78 1.78 1.78
3.5 dS / m
1.15 1.39 1.43 1.53 1.54 1.48 1.52 1.61
7.0 dS / m
0.84 0.84 1.32 1.31 1.36 1.38 1.52 1.62
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Cobos et al. Rev. Fac. Agron. (LUZ). 2022, 39(1): e223905
5-6 |
g. This result coincides with that described by Tavakkoli et al.,
(2011) who attribute the detrimental effect caused by salinity in
crops in early stages. They also agree with Cha-um and Kirdmanee
(2010), who state that rice with a salinity of 6.6 dS.m
-1
; suffers a
reduction in productivity of more than 50 %. Salt stress reduces
rice yield by reducing the number of lled grains per panicle and
the viability of pollen in plants. This study showed a signicant
decrease in grain weight in the evaluated phenological stages, as
saline concentration increased.
For thousand grains weight, the Tukey test (p> 0.05) determined
that the phenological stages of milky grain stage, owering,
booting and oral primordia had similar signicances (<0.0001),
reaching the higher weight values with 26.79, 26.68, 25.74, 25.44
g, respectively. The salinity level of 0.2 dS.m
-1
with a mean of 29.8
g was statistically higher (<0.0001) than other treatments, while the
lower weight was reached by the salinity level of 7.0 dS.m
-1
with
20.25 g. This agrees with Torabi et al (2013), who mention that
salinity is one of the main abiotic factors that affect the different
stages of growth, yield and quality of agricultural crops through the
stress they cause.
Regarding the interactions of the phenological stages of
germination, seedling, tillering, stem growth, oral primordia,
booting, owering and milky grain stage with the salinity level of
0.2 dS.m
-1
; they do not differ statistically (<0.0001), and they are
superior to other interactions. The phenological stages germination,
seedling and tillering, with the salinity level of 7.0 dS.m
-1
showed
the low results.
The variable chlorophyll content was recorded at 30, 45, 60
and 75 days. The phenological stage of germination had the lower
means with values of 36.95, 29.71, 23.24 and 19.53 %, respectively.
The salinity level 0.2 dS.m-1 with an average of 44.94, 38.23, 29.32
and 24.87 %, were statistically higher (<0.0001) than the other
treatments. The salinity level of 7.0 dS.m-1 had the lowest values.
In the interactions of the eight phenological stages x salinity levels,
the damage to the mesophyll cells was evident when the chlorophyll
content was or measured, and reduced as a result of increasing salts
levels in the treatments. These results agree with Sandoval et al.,
(2010) who mention that the ionic salinity factor lies in toxicity,
the ions that induce the most problems are chlorine and sodium,
although others such as nitrate, sulfate or ammonia are also toxic.
Its accumulation in the leaves produces marginal chlorosis and
with it, a decrease in the photosynthetic area, which determines
reductions in net photosynthesis. Ragab and Abd (2015) in their
study in Zea mays, comment that plants under conditions of saline
stress decrease the chlorophyll content and the rate of transpiration,
negatively affecting the photosynthetic activity.
Figure 5 shows the sensitivity of rice plants expressed as
signicant decrease in yield when subjected to salinity levels applied
at the beginning of each dened phenological phase (8 phases).
Critical stages of high sensitivity were detected between seedling
stage and tillering formation and even in the owering phase. On
the other hand, at milky grain phenological stage the salinity effect
was relatively low. Zeng and Shannon, (2000), mention that during
germination, rice is very tolerant to salinity, but it is very sensitive
in the seedlings and in the reproductive stages. However, it is less
sensitive during tillering and grain lling. Moreover, among the
most sensitive stages is the seedling and owering stage. These
results agree with Singh et al., (2004), who indicate that owering
is another highly sensitive growth stage in the crop life cycle, which
is affected by salinity stress.
Figure 5. Phases of high, medium and low sensitivity to salinity
during eight phenological stages of growth in rice
plants.
The result of this cluster analysis allowed the grouping of
phenological stages and salinity levels into four classes, which
delimited their similarity between the characteristics (Figure 6).
Class I (yellow), groupings with similar characters were 2-3
(Seedling - 7. 0 dS.m
-1
) and 1-3 (Germination - 7. 0 dS.m
-1
). Class
II (green) grouped to 8-2 (milky grain stage - 3.5 dS.m
-1
), 7-2
(Flowering - 3.5 dS.m
-1
), 6-2 (tillering - 3.5 dS.m
-1
), 5-2 (Floral
promordia - 3.5 dS.m
-1
), 8-3 (milky grain stage - 7. 0 dS.m
-1
), 7-3
(Flowering - 7. 0 dS.m
-1
), 4-2 (Stem growth - 3.5 dS.m
-1
) and 3-2
(Tillering- 3.5 dS.m
-1
).
In Class III (blue) are 6-3 (Booting - 7. 0 dS.m
-1
), 5-3 (Floral
Primordia - 7. 0 dS.m
-1
), 4-3 (Stem growth - 7. 0 dS.m
-1
), 3-3
(Tillering - 7. 0 dS.m
-1
), 2-2 (Seedling - 3.5 dS.m
-1
), which very
clearly grouped the phases in the salinity level of 7.0 dS.m
-1
. Finally,
Class IV (red) made up by the combination 8-1 (Milky grain stage -
0.2 dS.m
-1
), 7-1 (Flowering - 0.1 2 dS.m
-1
), 6-1 (Booting - 0.2 dS.m
-
1
), 2-1 (Seedling - 0.2 dS.m
-1
), 5-1 (Floral Primordia - 0.2 dS.m
-1
),
4-1 (Stem growth - 0.2 dS.m
-1
), 3-1 (Tillering - 0.2 dS.m
-1
), 1-1
(Germination - 0.2 dS.m
-1
), which grouped the eight phenological
phases with the control of 0.2 dS.m-1, clearly dening the low
salinity effects in the phenological phases.
Figure 6. Grouping of phenological stages and salinity levels
that shows similarity in characteristics, through
the analysis of conglomerate (Euclidean-Ward
Distance).
This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.
Rev. Fac. Agron. (LUZ). 2022, 39(1): e223905. January - March. ISSN 2477-9407.
6-6 |
Regarding Torabi et al. (2013) indicate that when there are high
levels of salinity, the absorption of water by the roots is greatly
reduced, the plants slow down their growth and come to present
symptoms of drought, such as wilting or blue-green coloration dark,
chlorosis and sometimes thicker waxy leaves. These symptoms
vary according to the phenology stage of the crop, being more
noticeable during the rst stages of growth. They mention that,
during germination, rice is very tolerant to salinity, but it is very
sensitive in the seedlings and in the reproductive stages. The high
levels of salinity in this stage affects the viability of the pollen,
which results in poor pollination and the consequent reduction in
the percentage of grains setting and, therefore, in the total yield
of the plant. In a recent study led by Mohammadi et al., (2010),
using various genotypes; it was found that most rice varieties show
reduced pollen viability under salinity conditions.
Conclusions
In rice, under greenhouse conditions the critical stages of high
sensitivity to salts were detected between seedling stage and tillers
formation and even in the owering phase, although at the stage of
lling the grain or milky grain stage, this effect was low.
High levels of salinity (3.5 and 7.0 dS.m
-1
) negatively inuence
many agronomic characters, components of owering and plant
growth, even shortening their vegetative cycle. This inuence is
most evident in the development of rice plants during germination,
seedling, tillering and stem growth phenological phase.
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