Agricultural Water Management 231 (2020) 106022

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Agricultural Water Management
journal homepage: www.elsevier.com/locate/agwat

Seed priming alleviated salinity stress during germination and emergence of
wheat (Triticum aestivum L.)

T

Faride Feghhenabia, Hashem Hadia,*, Habib Khodaverdiloob, Martinus Th. van Genuchtenc,daDepartment of Plant Production and Genetics, Urmia University, Urmia, Iran
Department of Soil Science, Urmia University, Urmia, Iranc
Department of Earth Sciences, Utrecht University, Utrecht, the NetherlandsdCenter for Environmental Studies, CEA, São Paulo State University, UNESP, Rio Claro, SP, Brazilb

ARTICLE INFOABSTRACT

Keywords:
Potassium silicate
Salinity response functions
Seed priming
Seedling
Emergence

Seed priming is known to often alleviate salinity stress during seed emergence and subsequent crop growth. This
study compares the effects of salinity stress on the germination and emergence of wheat (Triticum aestivum L.)
seeds untreated (control) and primed with ascorbic acid (Asc), potassium silicate (K2SiO3), proline (Pro),
spermidine (Spd) and Lake Urmia saline water (LUsw). Saline water from Lake Urmia (Iran) was diluted to
produce salinities with electrical conductivities (EC) of 2, 4, 6, 8, 10, 12, 14, 20 dS m−1, while distilled water (EC≈ 0 dS m−1) was used for the control. Two independent sets of experiments were conducted. The first experiments were used to select the most effective concentration of each priming agent based on the final germination
percentage (GP) and germination rate (GR). The second set of experiments aimed to analyze the measured datain terms of salinity response functions in order to quantitatively determine the most effective priming agent(s).
The first experiments showed that the most effective concentrations of Spd (0.5 mM), Pro (25 mM), K2SiO3(1.5 mM) and LUsw (100 mg L−1) mitigated the negative impacts of salinity on GR by 32, 18, 17 and 22 %,respectively. The second experiment showed that the Maas and Hoffman (1977) and van Genuchten and
Hoffman (1984) salinity response functions provided effective descriptions of seedling and early growth response to salinity stress. Mean values of the salinity threshold (EC*) and the salinity at which a given trait was
reduced by 50 percent (EC50) in these functions were 3.4 and 10.8 dS m−1 for the control, respectively. By
comparison, the EC* values for the K2SiO3, Pro, Spd and LUsw primed seeds were 5.3, 4.5, 4.7, and 4.2 dS m−1,
respectively, and the EC50 values were 12.4, 11.4, 11.9, and 9.4 dS m−1, respectively. The beneficial effects of
K2SiO3 on seedling growth were more evident than those of the other priming agents. K2SiO3 had the highest
effect on EC* and EC50 of the vitality index (VI), showing increases of 151 and 34 %, respectively. The highest
increases of EC* and EC50 for seedling dry weight (72 and 24 %, respectively) were obtained with Spd andK2SiO3. The findings provide much insight on relieving the negative effects of salinity through cost-effective seedpriming operations so as to improve the production of wheat under saline conditions.

1. Introduction
Soil salinity causes major losses in crop production, especially inarid and semi-arid regions where 110 million out of 270 million ha ofirrigated lands are located (Smedema and Shiati, 2002). Salinity is
becoming more extensive as a result of land clearing and unsustainableirrigation and salinity management practices, as well as increasingly bybringing marginal lands into production (Kang et al., 2013; Munns andGilliham, 2015; Kopittke et al., 2019). Salinity stress causes plants exposed to three major challenges, including increasing osmotic pressure,misbalancing ion uptake, and oxidative stress (Tahjib-Ul-Arif et al.,⁎2018). The response to this stress at each stage of growth varies not
only among plant species, but also among cultivars (Bojović et al.,2010). Most crop species are sensitive to salinity stress at early growthstages, including the germination and seedling establishment stages(Wang et al., 2009). During germination and emergence, plant survival
is likely the most vital indicator of salinity tolerance, whereas afterwards yield and growth reduction may be considered as the final tolerance criterion (Saadat and Homaee, 2015). The severity of salinity
stress is often determined best by measuring seedling growth since
rapid and uniform seedling emergence is a crucial prerequisite toachieve full yield potential and, ultimately, maximum profitability ofCorresponding author.
E-mail address: h.hadi@urmia.ac.ir (H. Hadi).

https://doi.org/10.1016/j.agwat.2020.106022
Received 20 September 2019; Received in revised form 6 January 2020; Accepted 7 January 2020
Available online 14 January 20200378-3774/ © 2020 Elsevier B.V. All rights reserved.

Agricultural Water Management 231 (2020) 106022

F. Feghhenabi, et al.

annual crops (Sadeghi and Robati, 2015).
There are several strategies to improve plant growth in salinity-affected environments. One strategy is through selection and breeding.
Numerous attempts have been made to improve the salt tolerance ofcrops using traditional breeding programs. Unfortunately, the complexity of the basic tolerance mechanisms involved, a lack of optimal
selection criteria, and variations in plant response to salinity at different
growth stages have resulted in limited commercial success (Taie et al.,2013). Another strategy is to prime the seeds with different agents and/or to use exogenous applications of these materials prior to theirplanting (Ali et al., 2017; Subramanyam et al., 2019). Many advocate
for this purpose the use of seed priming as a practical, cost-effective,
and low-risk alternative to improve seed germination and seedlingemergence by inducing the metabolic activity of pre-germination underadverse conditions (Jiménez-arias et al., 2015; Migahid et al., 2019).
Priming is not a simple emulation of the early imbibition stage ofgermination, but rather is thought to impose moderate stress on seeds,
which then activates a stress-responsive system that confers a “crosstolerance” on seeds when exposed to future stresses (Bhanuprakash andYogeesha, 2016). During pre-germination metabolic activities, structural (membrane protection during imbibition) and genetic repair, RNAand protein synthesis and antioxidant mechanism take place in primed
seed, which ensure its proper germination and seedling development(Saddiq et al., 2019). Several compounds such as silicon (Si), ascorbic
acid (Asc), salicylic acid (SA), and polyamines (PAs), have been proposed as signal transducers and messengers, if used as a leaf spray orsoil nutrient, or for seed priming, they may have profound effects onplant growth and development (Abu El-Soud et al., 2013; Kovácik et al.,2009). For example, proline is an organic osmolyte which if used as aseed priming, has been shown to enhance the GR and relative germination energy (RGE) of salinity-stressed rice seeds (Hua-long et al.,2014). Spermidine (Spd), a low-molecular-weight aliphatic amine, similarly improved GP, germination vigor, root viability and length,
while shortening the mean germination time under different water
stress conditions (Li et al., 2014). Ascorbic acid is one of the most important antioxidants in plants that alleviates different environmental
stresses. Silicon, the second most abundant mineral element on earth,
furthermore has been found to enhance markedly the capacity of antioxidants and to improve protein metabolism to moderate oxidative
stress (Geng et al., 2018).
Wheat (Triticum aestivum L.), which is one of the most importantfood crops in many parts of the world, often also suffers from salinity(Tuna et al., 2008). Numerous studies have noted the potential of seedpriming to ameliorate the effects of salinity stress on wheat growth(Bajwa et al., 2018; Jaafer et al., 2012; Saddiq et al., 2019). However,there are differences in the response of wheat varieties to salinity andseed priming. Moreover, little quantitative information exists about theresistance of wheat during germination and seedling emergence, especially about the possible effects of salinity and seed priming at theseedling stage.
Over the years, a number of salinity response functions have been
proposed for modeling plant tolerance to abiotic stresses, including
plant response to salinity stress (e.g., Maas and Hoffman, 1977; van
Genuchten and Hoffman, 1984). To our knowledge, such functions havenot been generally used to assess the effects of seed priming on plant
response to salinity stress. In this study we will apply the empiricalresponse functions of Maas and Hoffman (1977) and van Genuchten
and Hoffman, 1984) to identifying the most effective seed priming
agents for lessening the effects of different salinity levels (up to
20 dS m−1) at the seedling stage. Specific objectives hence are to 1)
investigate the ability of five different seed priming agents, notably
spermidine (Spd), ascorbic acid (Asc), proline (Pro), potassium silicate(K2SiO3) and Lake Urmia saline water (LUsw), to improve the germination potential of wheat (Triticum aestivum L.) subject to salinity stress,
and 2) quantify the response of wheat to salinity using response functions to investigate the performance of the seed priming agents at theseedling stage.
2. Materials and methods
All experiments were carried out at the Seed Technology Laboratoryof the Agricultural Faculty of Urmia University (Urmia, Iran) during2017. Wheat seeds (of the Chamran variety of Triticum aestivum L.) were
provided by the Cereal Laboratory of the Agricultural Research Centerof West Azerbaijan Province, Urmia, Iran. Mean seed dry weight per
100 seeds was 3.57 g, while the seed moisture content ranged from 9 to
10 %. Separate studies prior to the experiments showed that seeds exhibited a 100 % germination percentage at a temperature of 25 °C as
assessed using Petri dishes. The seeds were surface-sterilized in a 1 %sodium hypochlorite solution for 10 min, then rinsed with distilledwater and dried before being used in the germination tests.
The experiments were implemented in two consecutive phases. The
first phase aimed to evaluate the final germination percentage (GP) andgermination rate (GR) of the seeds. This enabled us to obtain somepreliminary data regarding plant response to different concentrations of
the various seed priming agents (and for a control using untreatedseeds) at the imposed salinity levels. The experiments allowed us toselect the best concentrations of the various seed priming agents to be
used for the next phase. For the priming we soaked the seeds into solutions containing spermidine (Spd) (0, 0.5, 1 and 1.5 mM) for 10 h,
ascorbic acid (Asc) (0, 50, 75 and 100 mM) for 24 h, or proline (Pro) (0,12, 17 and 20 mM) for 2 days, potassium silicate (K2SiO3) (0, 1, 1.5 and2 mM) for 6 h, or Lake Urmia saline water (LUsw) (0, 100, 150 and
200 mg L−1 salt) for 10 h. These materials and their specific concentrations were selected following previous studies using similar
agents (Ahmed et al., 2016; Ibrahim, 2016; Sivritepe et al., 2003;
Torabi et al., 2012). Also, we note that Lake Urmia water was used,rather than artificial solutions, since the ionic solution composition ofmost nearby soils were fairly similar to that of the lake. Once primed,
the seeds were thoroughly rinsed with tap water followed by distilledwater, dried back to their original moisture content at room conditions(about 25 °C and 42 % relative humidity) as determined by changes inseed weight. All seeds subsequently were surface-sterilized in a 1 %sodium hypochlorite solution for 10 min for use in the main experiments.
For the first phase we used nine salinity levels with electrical conductivities of 0, 2, 4, 6, 8, 10, 12, 14 and 20 dS m−1. The salinity levels
were obtained by diluting saline water from Lake Urmia located innorthwest Iran. Samples of 300 treated seeds (three replicates of 100
seeds) were placed in covered 9-cm diameter Petri dishes containing asingle filter paper moistened with 7 ml of each saline water treatment.
The Petri dishes were placed in a germinator at 25 ± 2 °C. Data werecollected every 6 h until no additional germination occurred for 48 h. At
the end of the experiments, the final GP and GR values were calculated
after Sajirani et al. (2011). GR is generally considered to be the mostimportant criterion since it reflects the vigor of the seeds. The mostefficient concentration of every seed priming agent was selected from a
linear regression of a particular trait (such as GP or GR) versus salinity.
The concentration of a given priming agent that provided a regression
line with the lowest slope was presumed to be the most effective concentration of that priming agent (Maggio et al., 2004; Steppuhn et al.,2005), and then used in subsequent experiments.
The second phase of the experiments was used to test, for each
optimal concentration of the agents, the effects of the same range ofsalinities on seedling development over a period of 14 days. Theseexperiments were carried out in a greenhouse having a temperature of
approximately 25 °C during the day and 20 °C at night, a relative humidity of 50 ± 10 %, and a light intensity of 700 μmol m−2s-1. We
used for these experiments 16-cm high, 7-cm diameter PVC pots packed
with 540 g farm soil. The loam soil (sand, silt and clay percentages were46, 33 and 21 %, respectively) was non-saline (the electrical conductivity of the saturation paste was 1.1 dS m−1), contained 18.5 %2

Agricultural Water Management 231 (2020) 106022

F. Feghhenabi, et al.

equivalent CaCO3, and had a pH of 7.7. We sowed 10 seeds per pot,
which were thinned to 5 seedlings per pot after emergence. For every
treatment we used three replicates, thus providing us with data from
270 different pots (5 priming agents, 9 salinities, 2 phases, 3 replicates).
The various experiments produced estimates of the following traits:
Final maximum seed emergence percentage, Emax, being theratio of the number of seeds emerged over the total number of seeds
sown (×100 %).
Emergence rate, R50, being the rate at which 50 % of the seeds
emerged: R50 = 1/D50, where D50 is the number of days needed to reach
50 % of emergence.
Vitality index, VI, given by the length of the seedlings × Emax
Reciprocal of the emergence uniformity, REU, given by
REU = 1/EU where EU = D90-D10. D10 and D90 are the number of days
needed to reach 10 and 90 % emergence, respectively. As the difference
between D10 to D90 increases, the emergence uniformity (EU) hence
decreases and REU increases.
Seedling growth indexes given by certain seedling attributes suchas length, dry weight and fresh weight 16 days after planting.
Weight of mobilized seed reserve, WMSR, given by the dryweight of the original seed minus the dry weight of the seed remnant.
The initial seed dry weight was found to be 0.033 ± 0.006 g per seed.
The effects of seed priming and salinity on the various traits were
investigated using several empirical salinity response functions.
Traditionally the most popular response function has been the linear
threshold slope model introduced by Maas and Hoffman (1977).
Written in terms of the soil electrical conductivity, EC, this responsemodel is given by(EC ) = 1

0 EC EC *EC *) EC * < EC EC * + 1/ b
EC > EC * + 1/b

1
b (EC
0

different numbers of fitting parameters, and more fitting parameters
normally will lead to a better fit (i.e. lower SSE values), the Akaike
information criterion (AIC) was used to compare the performance of themodels. When the number of data-points (n) is small in comparison to
the number of fitting parameters (q), such as in our study where n exceeds the number of fitting parameters by only four or five, one may use
the corrected AIC (Bolster and Hornberger, 2007; Razzaghi et al., 2016)
as follows:

AIC = nln

1
1 + (EC / EC50 ) p

P=

1
1 + [(EC

0 EC EC *1
EC > EC *EC *)/(EC50 EC *)]pe 0.5
1 + e 0.5

(6)in which Δ is the absolute difference between the AIC values of the two
response functions being evaluated. P values were used to ensure thatthe decrease in SSE, required to accept the more accurate response
function, is reasonable (Bolster and Hornberger, 2007; Razzaghi et al.,2016).
Statistical operations, calculations, and fitting of response function
models were performed using Excel 2013 software and its Solver extension.
3. Results and discussion
3.1. Seed germination as influenced by salinity and priming(1)

The germination percentage (GP) and germination rate (GR) wereboth found to decrease with increasing salinity levels for both thecontrol and the primed seeds (Figs. 1 and 2). However, the impact ofsalinity on GR was higher than on GP, with GR showing an almost 50 %reduction at EC = 20 dS m−1, while GP decreased by only 23 %. Actually, 20 % of the total reduction in GP occurred between 2 and 8 dS m1, while this amount was 45 % for GR. The main reasons for the higher
sensitivity of GR to salinity as compared to GP could be attributed to thedamages that salinity causes to the enzymes involved in germination or
the delay in their activity (KhoshKholgh Sima et al., 2013). Except for
Asc, all seed priming agents alleviated the inhibitory effect of salinity
stress on GP and GR. Many studies have shown that a capability to
rapidly re-start both Asc biosynthesis and APX activity is necessary forsuccessful seed germination. However, other studies (e.g., Takemura
et al., 2010) acknowledged that high Asc treatment may cause the(2)where EC50 is the soil salinity at which α(EC) is reduced by 50 percent,and p is a dimensionless shape parameter, presumably a function of
specific crop, soil and climate conditions. For many crops, the value of p
on average was found to be about 3 when Eq. (2) was applied to salinity
stress data (van Genuchten and Gupta, 1993). As shown by Steppuhn
et al. (2005) and van Genuchten and Gupta (1993), among others, Eq.
(2) was found to describe crop salt tolerance data equally well or better
than Eq. (1).
Dirksen et al. (1993) later included a threshold salinity in Eq. (2) toenable a more flexible description of salinity response data at low
salinities:(EC ) =

(5)

The response function with the lowest value of AIC will be assumed
to be the most accurate. To test if the improved accuracy is statisticallysound and justifies the extra parameters, the probability will be calculated using (Bolster and Hornberger, 2007; Razzaghi et al., 2016):

where α is the specific trait being considered in relative terms (0≤α≤1)
as a function of soil salinity, EC (dS m−1), EC* is the salinity thresholdvalue and b is the slope of the response function. Since the linearity
assumption of Eq. (1) often does not fully meet actual field conditions,van Genuchten and Hoffman (1984) proposed an alternative S-shaped
function of the form:(EC ) =

2(q + 1)(q + 2)
SSE
+ 2(q + 1) +
n
n q 2

(3)

The above macroscopic response functions were fitted to the observed data by minimizing the sum of the squared errors (SSE) between
measured (Oi) and model-predicted (Pi) values of the dependent variable using unweighted least-squares regression (e.g., van Genuchten,1983):
Fig. 1. Effect of salinity on the germination percentage of wheat untreated(Con, control) or primed with the most effective concentrations of the seedpriming agents Spd (spermidine), Pro (proline), K2SiO3 (potassium silicate) and
LUsw (Lake Urmia saline water) used in this study.

n

SSE =

(Pi
i=1

Oi) 2

(4)

where n is number of data-points. Since the response functions have3Agricultural Water Management 231 (2020) 106022

F. Feghhenabi, et al.

Fig. 2. Effect of salinity on the germination rate of wheat untreated (Con,control) or primed with the most effective concentrations of the seed priming
agents Spd (spermidine), Pro (proline), K2SiO3 (potassium silicate) and LUsw
(Lake Urmia saline water) used in this study.

destruction of mesothelioma cells and prevent germination in wheat
seeds (Takemura et al., 2010). In agreement with these results, not only
did none of the concentrations of Asc in our study have a positive effect,
they actually reduced markedly the GP.
The priming concentrations that produced the lowest reduction (lessnegative slope) (Maggio et al., 2004; Steppuhn et al., 2005), and hence
most likely the highest increases in the GR and GP values, were used insubsequent experiments. Ultimately, selected concentrations were
0.5 mM for Spd, 25 mM for Pro, 1.5 mM K2SiO3, and 100 mg L−1 for
LUsw (Figs. 1 and 2). The most effective concentrations of Spd, Pro,
K2SiO3 and LUsw mitigated the negative impacts of salinity on GR by
32, 18, 17 and 22 %, respectively, with their moderating effect on GP
always being less than 15 % (up to 3, 11, 11 and 9 %, respectively).
Seed priming hence had far more effect on the wheat germination rate
than on the germination percentage. Experimentally, higher GR valuesof primed seeds are due to metabolic repair, with more metabolite
production required for germination during the imbibition process(Saddiq et al., 2019). Moreover, Hua-Long et al. (2014) showed that the
improvement of GR for primed seeds with Pro was mainly due to anincrease in intracellular osmolytes and alleviation of water uptake imbalances during germination phases II and III.
3.2. Seedling emergence as influenced by salinity and priming
Salinity had a major inhibitory effect on the growth and development of seedlings as shown in Fig. 3, which provides results for the fourmost important traits we investigated. Quantitative parameters representing the effects of salinity on seedling growth and development
are listed in Table 1 for all traits. Please note that all values in Fig. 3 are
relative, calculated as the value of the attribute for each level oftreatment (salinity and seed priming) relative to the control (i.e., thevalue at zero salinity and without seed priming). Hence, every value
simultaneously reflects the coupled effects of salinity and seed priming.
The responses of the traits versus salinity were almost the same.
However, the intensities of the responses to salinity were not the sameamong all salinity levels. The effects at lower levels of salinity weregenerally milder, with most traits showing a negligible change up tocertain threshold salinity, while the inhibitory effects of salinity on thetraits increased beyond a certain threshold salinity (Fig. 3a–d). For
example, the relative values of Emax and R50 changed slightly to
EC = 12 and 4 dS m−1, respectively, after which they declined by almost 87 and 82 %, respectively, to EC = 20 dS m−1. In the same way,
for all of the seed priming agents, the values of the traits decreased only
modestly at low salinities. The changes were greater at higher salinities.
It seems that the behavioral patterns of the traits versus salinity did notchange much by seed priming. However, the rate of decrease and theFig. 3. Effect of salinity on relative values of Emax (a), R50 (b), VI (c) andseedling dry weight (d) of wheat untreated (Con, control) or primed with themost effective concentrations of the seed priming agents seed priming agentsSpd (spermidine), Pro (proline), K2SiO3 (potassium silicate) and LUsw (Lake
Urmia saline water) used in this study.

4Agricultural Water Management 231 (2020) 106022

F. Feghhenabi, et al.

Table 1
Obtained values of parameters in the van Genuchten and Hoffman (1984) andMaas and Hoffman (1977) salinity response functions to quantitatively show
the effect of various priming agents used in this study to cope with salinity
stress.
Trait1

Emax (%)

R50 (1/day)

REU (1/day)VI

Seedling length (cm)

Seedling fresh weight (g)Seedling dry weight (g)WMSR (g)Parameter2

EC*
b
EC50
p
EC*
b
EC50
p
EC*
b
EC50
p
EC*
b
EC50
p
EC*
b
EC50
p
EC*
b
EC50
p
EC*
b
EC50
p
EC*
b
EC50
p

Seed priming agent3
Control

Pro

K2SiO3

Spd

LUsw

12.3
0.106
16.2
8.6
1.6
0.051
9.7
2.5
0.0
0.048
8.6
2.6
2.2
0.061
9.3
3.4
2.6
0.060
9.9
3.4
2.3
0.058
9.7
3.3
2.2
0.056
10.2
2.9
4.2
0.054
12.5
3.4

16.2
0.202
16.4
7.7
1.9
0.062
9.7
3.0
0.0
0.039
8.3
1.9
3.5
0.064
10.3
3.6
3.3
0.058
10.7
3.2
2.7
0.051
10.3
2.8
2.1
0.053
10.6
2.6
6.5
0.058
14.7
3.9

16.2
0.194
17.7
9.3
2.1
0.048
10.8
2.4
2.0
0.065
8.6
3.8
5.6
0.066
12.5
5.1
5.2
0.058
12.9
4.1
3.2
0.053
11.3
3.0
3.7
0.050
12.7
2.9
4.6
0.054
13.0
3.2

15.4
0.172
17.3
10.7
1.8
0.055
9.9
2.9
2.5
0.050
9.1
2.9
3.8
0.063
11.3
3.9
3.5
0.056
11.8
3.2
3.3
0.055
11.0
3.1
3.8
0.051
12.3
2.9
3.5
0.050
12.9
2.8

14.5
0.113
17.7
7.2
2.0
0.053
10.3
2.7
0.0
0.053
7.6
2.2
3.4
0.056
10.5
3.7
3.6
0.055
11.2
3.4
2.8
0.058
10.1
3.3
3.5
0.054
11.3
3.0
3.7
0.054
12.2
2.9

Fig. 4. Seedling growth of wheat in response to different concentrations ofsalinity for (a) the control (no seed priming), and (b) primed with K2SiO3. A
considerable effect of seed priming was observed for intermediate salinities(i.e., for salinity levels of between 6 and 12 dS m−1).

Genuchten and Hoffman (1984) and the Maas and Hoffman (1977)
functions were −33.9 and −34.6 and −23.9 and −25.6, respectively.
The mean and median AIC values were, respectively, −18.1 and −17.5
for the Dirksen et al. (1993) function. The first to third quartile valuesof the AIC for the van Genuchten and Hoffman (1984) function were
within the range of −38.8 to −29.9, while they varied from −29.5 to−19.9 for the Maas and Hoffman (1977) function, and from −24.7 to−13.0 for the Dirksen et al. (1993) response function (Fig. 6). While
there was generally no statistically significant difference between either
the Maas and Hoffman (1977) and the Dirksen et al. (1993) functions or
the van Genuchten and Hoffman (1984) and Maas and Hoffman (1977)
functions in terms of their AIC values (P ≥ 0.05), the van Genuchten
and Hoffman (1984) response function provided fits that were statistically superior (P < 0.05) to the Dirksen et al. (1993) function.
Table 1 lists, for all five priming agents, the fitted parameters of the van
Genuchten and Hoffman (EC50 and p) and Maas and Hoffman (EC* andb) response functions.

1

final maximum emergence (Emax), emergence rate based on the rate
reaching 50 % emergence (R50), reciprocal of the emergence uniformity (REU),
vitality index (VI), weight of mobilized seed reserve (WMSR).
2
salinity threshold at which the reduction begins (EC*), reduction slope in
response to salinity (b), EC at which trait is reduced by 50 percent (EC50), dimensionless empirical shape parameter (p).
3control (Con), ascorbic acid (Asc), proline (Pro), potassium silicate(K2SiO3), spermidine (Spd), Lake Urmia saline water (LUsw).

threshold EC changed, with the changes not being the same among thedifferent seed priming agents. As an example, Fig. 4 visually shows theeffects of salinity on seedling growth for the control and the K2SiO3treated seeds.
In general, all priming agents considerably alleviated the adverse
effects of salinity (Fig. 3). The positive effects of seed priming in ourstudy can be considered from two perspectives: i) lessening the rate of
the salinity-induced decline of the traits, and ii) delaying the start of thedeclining trend in the measured traits. Priming was more efficient interm of the second perspective.
The effects of salinity and seed priming on the various traits wereanalyzed next in terms of the numerical salinity response functions.
Fig. 5 shows the overall fit of the salinity response functions for Emax,
R50, VI and seedling dry weight for both the control and priming with
K2SiO3, the latter being the most efficient priming agent. Relative values of the traits remained more or less constant until they reachedsome threshold EC, beyond which they decreased.
A box plot of the Akaike information criterion (AIC) for the response
functions over all of the traits considered showed that the van
Genuchten and Hoffman (1984) response function had the lowest AIC
values, followed by the Maas and Hoffman (1977) and Dirksen et al.
(1993) functions (Fig. 6). Mean and median AIC values for the van

3.3. Quantitative effects of seed priming on plant response to salinity
Increasing the salinity caused the values for all emergence indices todecrease for the control and all priming agent. For example, Emax for thecontrol began to decrease at EC = 12.3 dS m−1 (EC*) and was loweredby 50 percent (EC50) at EC = 16.2 dS m−1. This trait was the least affected by salinity (see also Fig. 5a). We note here that all seed priming
agents improved seed emergence such that the average EC* and EC50
values increased to 15.6 and 17.3 dS m−1, respectively. The most effective seed priming agents for Emax was K2SiO3, which increased EC* to16.2 dS m−1 and EC50 to 17.7 dS m−1.
The lowest EC* value of the emergency rate (R50) was observed forseedlings of the control (EC* = 1.6 dS m−1), and the highest value forK2SiO3-treated seedlings (2.1 dS m−1). On the other hand, seed priming
decreased the seedling sensitivity to salinity by increasing EC* for R50.
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F. Feghhenabi, et al.

Fig. 6. Box plot of the Akaike information criterion (AIC) values for comparison
among the response functions used, as averaged over all of the traits studied.

R50. Nonetheless, b for R50 increased with other priming agents. Consequently, a comparison of the parameters for Emax and R50 showed thatthe sensitivity of R50 to salinity was more than Emax. Besides, the abilityof seed priming to alleviate the adverse effects of salinity on EC50 ofboth traits was very similar. Still, the greater difference between EC* ofthe control and the primed seeds for Emax, as compared to R50, indicatesthat seed priming was more efficient in reducing the adverse effects ofsalinity on Emax.
A comparison of reciprocal emergence uniformity (REU) values asaffected by seed priming shows that all priming agents had very little
effect. EC*and EC50 increased only with K2SiO3 and Spd. REU values
obtained with Pro and LUsw priming showed slightly lower EC50 values
compared to the control. Also, b of REU using Pro as the priming agent
decreased slightly while increasing for the other priming agents relative
to the control.
EC* and EC50 for the control vitality index (VI) were 2.2 and9.3 dS m−1, respectively. The positive effect of priming on VI is shownby the increased values of EC* and EC50. K2SiO3 and LUsw had the mostand least effect on EC* (151 % and 53 % higher than the control EC*,
respectively). Furthermore, priming raised EC50 by an average of
11.1 dS m−1, of which K2SiO3 and Spd exceeded the average. On theother hand, b increased when using K2SiO3, Pro and Spd, but decreased
with LUsw priming.
Increasing the salinity caused seedling length to decrease. A possible
reason for reducing seedling length, one of emergence indices, may be
due to lowering the turgor pressure at relatively high salinities as aconsequence of slowing down water uptake by the seedlings, whichshould reduce cell enlargement (Migahid et al., 2019) and may shorten
the shoot (Izzo et al., 1991). Another probable reason is a reduction in
the mobilized seed reserve (WMSR). During seed germination undersalinity, not only seed reserve utilization decreases, but also its efficiency, because of increased respiration so that the dry weight ofgrowing seedlings always became lower than that of the mobilized
substrates (Chen and Arora, 2011). However, seed priming had a positive effect on seedling length. As an example, EC* for seedling length
increased up to 24, 97, 33 and 36 % using Pro, K2SiO3, Spd and LUsw,
respectively, compared to the control. By comparison, the value of b
was not significantly affected by priming. Seed priming similarly increased EC50 of seedling length by an average of 17 % relative to thecontrol EC50. The effects of Pro and K2SiO3 on seedling length were,respectively, the least and most significant compared to the other seedpriming agents.
The adverse effects of salinity on seedling fresh weight were compensated by increasing EC* and EC50 for all seed priming agents.
Seedling fresh weight for the control was not affected by EC up to
2.3 dS m−1. The highest EC* and EC50 values (the averages increased 41
and 15 %, respectively) were obtained using Spd and K2SiO3.

Fig. 5. Overall fit of the applied response functions to the experimental data for
Emax (a), R50 (b), VI (c) and seedling dry weight (d) versus salinity for thecontrol and the K2SiO3 primed seeds.

R50 of the control seedlings decreased by 50 percent (EC50) at
EC = 9.7 dS m−1, while the EC50 values for Pro, K2SiO3, Spd and LUsw
were 9.7, 10.8, 9.9 and 10.3 dS m−1, respectively (Table 1). Among theseed priming agents, only K2SiO3 slightly decreased the value of b for
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The EC* and EC50 values of seedling dry weight, which for thecontrol were 2.2 and 10.2 dS m−1, respectively, increased also withseed priming (except for EC* for Pro). The highest increases of EC* andEC50 (72 and 24 %, respectively) were obtained with Spd and K2SiO3.
Although Pro reduced EC* by 0.1 dS m−1, it increased EC50 of seedling
dry weight by 0.4 dS m-1 and decreased b by 0.003. Other seed priming
agents reduced b as well.
The most significant differences between the various seed priming
agents were obtained for the weight of the mobilized seed reserve(WMSR), especially in terms of EC*, but also EC50 (Table 1). While
WMSR declined with salinity for all seed priming agents and the control, the salinity thresholds for Spd and LUsw were less than those of thecontrol and the other priming agents. By comparison, WMSR for Pro
had the highest EC* and EC50, values (6.5 and 14.7 dS m−1, respectively). Although the positive effect of K2SiO3 for WMSR was not asmuch as those of Pro, K2SiO3 priming was able to increase EC* and EC50
by 10 and 4.1 %, respectively. b only increased by Pro. Our WMSR
findings are in agreement with recent studies by Bhanuprakash andYogeesha (2016), who reported that seed priming increased seed reserve utilization, seedling dry weight and the seed reserve depletion ofmountain rye and wheat.
The seed priming agents in most cases positively changed EC*, b andEC50 for emergence and the other seedlings qualities, although eachpriming agent had its unique impact on the traits. As a general trend,
the effect of seed priming was most pronounced for the EC* and EC50
indices. Values of EC* seemed to have been influenced by seed priming
more than the other parameters, with the highest increases occurring
for the vitality index (83 %) and seedling length (48 %). However, allseed priming agents had a positive effect on the seedling traits, with
K2SiO3 being the best. Paul et al. (2017) and Shi et al. (2014) concluded
that improvements of seed germination and reductions in the effects ofoxidative stress on seedlings primed with Spd and Si were due toboosting the antioxidant defense. Our findings on the valuable effects ofseed priming are consistent also with those reported by Anaya et al.
(2018) for broad bean and Patanè et al. (2009) for sweet sorghum.
When averaged over all the traits, seed priming increased theminimum, maximum and mean salinity thresholds, EC*, compared tothe control (Table 1). For the most effective priming agent (K2SiO3),
these cardinal points were 2.0, 16.2 and 5.3 dS m−1, respectively,
compared to 0.0, 12.3 and 3.4 dS m−1 for the control (Table 1). Similar
increases, although less pronounced, were observed for all otherpriming agents. For example, the EC* values averaged over all traits
increased to 4.5, 4.7, and 4.2 dS m−1 for the Pro, Spd and LUsw priming
agents, respectively. Moreover, the minimum and maximum EC50 for
the control treatment, which were 8.6 and 16.2 dS m−1, respectively,
were 8.6 and 17.7 dS m−1 for K2SiO3, the most effective pretreatment(Table 1). But all seed priming agents had a positive effect: the mean
EC50 as averaged over all traits increased from 10.8 for the control to
11.4, 12.4, 11.9, and 11.4 dS m−1 for the Pro, K2SiO3, Spd and LUsw
priming agents, respectively. Among the various traits, the mean EC*
and EC50 (again, as averaged over all seed priming agents) improved
most for the vitality index (VI), seedling length and seedling dry weight.
Interestingly, the entries in Table 1 show that seed priming in general
had little effect on the p value of the van Genuchten and Hoffman(1984) salinity response function (Eq. 2), although some exceptions areapparent (especially for Emax). The average value of p for most cases
remained very close to 3.0 as noted by van Genuchten and Gupta(1993) for many crops.

salinity stress. The principle purpose of this study was to quantitatively
analyze seedling response to the simultaneous effects of salinity andseed priming. Analyses of our data showed that the salinity response
functions of van Genuchten and Hoffman (1984) and Maas andHoffman (1977) were able to describe the response of seedlings tosalinity and seed priming with remarkable accuracy. The functions andtheir parameters provided useful insight into the overall effects ofpriming and salinity, including showing that K2SiO3 was the most effective priming agent.
While overall findings of our study confirmed the positive effects ofseed priming on seed germination and establishment under salineconditions, more investigations on plant response to salinity andpriming are needed, not only during early growth stages and using
salinized soils (in our case we used saline water from Lake Urmia), butalso with naturally salinized soils and for different environments.
Especially needed are studies investigating whether the positive effects
of seed priming on growth can be extrapolated to entire growth periods.
Results of such studies covering the complete plant life cycle would
provide much practical information for crop management in saline
environments.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence the work reported in this paper.
References
Abu El-Soud, W., Hegab, M.M., Abd Elgawad, H., Zinta, G., Asard, H., 2013. Ability ofellagic acid to alleviate osmotic stress on chickpea seedlings. Plant Physiol. Biochem.
71, 173–183.
Ali, Q., Daud, M.K., Haider, M.Z., Ali, S., Rizwan, M., Aslam, N., Noman, A., Iqbal, N.,
Shahzad, F., Deeba, F., Ali, I., Zhu, S.J., 2017. Seed priming by sodium nitroprusside
improves salt tolerance in wheat (Triticum aestivum L.) by enhancing physiologicaland biochemical parameters. Plant Physiol. Biochem. 119, 50–58.
Ahmed, M., Qadeera, U., Ahmed, Z.I., Hassan, F., 2016. Improvement of wheat (Triticum
aestivum) drought tolerance by seed priming with silicon. Arch. Agron. Soil Sci. 62(3), 299–315.
Anaya, F., Fghire, R., Wahbi, S., Loutfi, K., 2018. Influence of salicylic acid on seedgermination of Vicia Faba L. under salt stress. J. Saudi Soc. Agric. Sci. 17 (1), 1–8.
Bajwa, A.A., Farooq, M., Nawaz, A., 2018. Seed priming with sorghum extracts andbenzyl aminopurine improves the tolerance against salt stress in wheat (Triticum
aestivum L.). Physiol. Mol. Biol. Plants 24 (2), 239–249.
Bhanuprakash, K., Yogeesha, H.S., 2016. Seed priming for abiotic stress tolerance: an
overview. In: Srinivasa Rao, N.K., Shivashankara, K.S., Laxman, R.H. (Eds.), Abiotic
Stress Physiology of Horticultural Crops. Springer, pp. 103–117.
Bojović, B., Đelić, G., Topuzović, M., Stanković, M., 2010. Effects of NaCl on seed germination in some species from families Brassicaceae and Solanaceae, Kragujevac J.
Sci . 32, 83–87.
Bolster, C.H., Hornberger, G.M., 2007. On the use of linearized Langmuir equations. Soil
Sci. Soc. Am. J. 71 (6), 1796–1806.
Chen, K., Arora, R., 2011. Dynamics of the antioxidant system during seed osmopriming,
post-priming germination and seedling establishment in spinach (Spinacia oleracea).
Plant Sci. 180 (2), 212–220.
Dirksen, C., Kool, J.B., Koorevaar, P., van Genuchten, M.Th., 1993. HYSWASOR, simulation model of hysteretic water and solute transport in the root zone. In: Yaron, D.,
Dagan, G. (Eds.), Water Flow and Solute Transport in Soils. Springer, New York, pp.
99–122.
Geng, A., Wang, X., Wu, L., Wang, F., Wu, Z., Yang, H., Chen, Y., Wen, D., Liu, X., 2018.
Silicon improves growth and alleviates oxidative stress in rice seedlings (Oryza sativa
L.) by strengthening antioxidant defense and enhancing protein metabolism underarsanilic acid exposure. Ecotoxicol. Environ. Saf. 158, 266–273.
Hua-Long, L., Han-Jing, S., Jing-Guo, W., Yang, L., De-Tang, Z., Hong-Wei, Z., 2014.
Effect of seed soaking with exogenous proline on seed germination of rice under salt
stress. J. Northeast Agric. Univ. 21 (3), 1–6.
Ibrahim, E.A., 2016. Seed priming to alleviate salinity stress in germinating seeds. J. Plant
Physiol. 192, 38–46.
Jaafer, M.Z., Farooq, M., Cheema, M., Afzal, I., Basra, S.M.A., Wahid, M.A., Aziz, T.,
Shahid, M., 2012. Improving the performance of wheat by seed priming under salineconditions improving the performance of wheat by seed priming under saline conditions. J. Agron. Crop Sci. 198, 37–45.
Jiménez-Arias, D., Borges, A.A., Luis, J.C., Valdés, F., Sandalio, L.M., Pérez, J.A., 2015.
Priming effect of menadione sodium bisulphite against salinity stress in arabidopsis
involves epigenetic changes in genes controlling proline metabolism. Environ. Exp.
Bot. 120, 23–30.
Kang, S., Post, W.M., Nichols, J.A., Wang, D., West, T.O., Bandaru, V., Izaurralde, R.C.,

4. Conclusions
Our study showed that seed priming improved the salt tolerance of
wheat seedlings. This was supported by increasing values of several
traits under salinity stress. Seed priming increased the vitality index,
seedling length and seedling dry weight compared to other traits, improved the development of seedlings, and mitigated the effects of7

Agricultural Water Management 231 (2020) 106022

F. Feghhenabi, et al.
2013. Marginal lands: concept, assessment and management. J. Agric. Sci. 5 (5),129–139.
KhoshKholgh Sima, N.A., Alitabar, R., Eqbalinejad, M., Babazadeh, P., Taleh Ahmad, S.,
2013. Effect of salinity on germination and threshold salinity in barley. Iran. J. Field
Crop Res. 11 (1), 107–120.
Kopittke, P.M., Menzies, N.W., Wang, P., McKenna, B.A., Lombi, E., 2019. Soil and theintensification of agriculture for global food security. Environ. Int. 132, 105078.
Kovácik, J., Klejdus, B., Hedbavny, J., Backor, M., 2009. Salicylic acid alleviates NaClinduced changes in the metabolism of matricaria chamomilla plants. Ecotoxicology
18 (5), 544–554.
Li, Z., Peng, Y., Zhang, X.Q., Ma, X., Huang, L.K., Yan, Y.H., 2014. Exogenous spermidine
improves seed germination of white clover under water stress via involvement instarch metabolism, antioxidant defenses and relevant gene expression. Molecules 19,
18003–18024.
Maas, E.V., Hoffman, C.J., 1977. Crop salt tolerance-current assessment. J. Irrig. Drain.
Div. 103, 110–134.
Migahid, M.M., Elghobashy, R.M., Bidak, L.M., Amin, A.W., 2019. Priming of Silybum
marianum (L.) Gaertn seeds with H2O2 and magnetic field ameliorates seawater stress.
Heliyon 5 (6), e01886.
Maggio, A., De Pascale, S., Angelino, G., Ruggiero, C., Barbieri, G., 2004. Physiologicalresponse of tomato to saline irrigation in long-term salinized soils, Europ. J.
Agronomy . 21 (2), 149–159.
Munns, R., Gilliham, M., 2015. Salinity tolerance of crops – what is the cost? New Phytol.
208, 668–673.
Patanè, C., Cavallaro, V., Cosentino, S.L., 2009. Germination and radicle growth in unprimed and primed seeds of sweet sorghum as affected by reduced water potential in
NaCl at different temperatures. Ind. Crop Prod. 30, 1–8.
Paul, S., Roychoudhury, A., Banerjee, A., Chaudhuri, N., Ghosh, P., 2017. Seed pretreatment with spermidine alleviates oxidative damages to different extent in the salt
(NaCl)-stressed seedlings of three indica rice cultivars with contrasting level of salt
tolerance Saikat. Plant Gene 11, 112–123.
Razzaghi, S., Khodaverdiloo, H., Ghorbani Dashtaki, S., 2016. Effects of long-term wastewater irrigation on soil physical properties and performance of selected infiltration
models in a semi-arid region. Hydrol. Sci. J. 61 (10), 1778–1790.
Saadat, S., Homaee, M., 2015. Modeling sorghum response to irrigation water salinity at
early growth stage. Agr. Water Manag. 152, 119–124.
Sadeghi, H., Robati, Z., 2015. Response of cichorium intybus L. to eight seed priming
methods under osmotic stress conditions. Biocatal. Agric. Biotechnol. 4 (4), 443–448.
Saddiq, M.S., Iqbal, S., Afzal, I., Ibrahim, A.M.H., Bakhtavar, M.A., Hafeez, M.B.,
Maqbool, J., Maqbool, M.M., 2019. Mitigation of salinity stress in wheat (Triticum
aestivum L.) seedlings through physiological seed enhancements. J. Plant Nutr. 42(10), 1–13.

Sajirani, B.E., Shakouri, M.J., Mafakheri, S., 2011. Borage (Borago Officinalis L.) germination under saline condition. Ann. Biol. Res. 2 (6), 414–416.
Shi, Y., Zhang, Y., Yao, H., Wu, J., Sun, H., Gong, H., 2014. Silicon improves seed germination and alleviates oxidative stress of bud seedlings in tomato under water
deficit stress. Plant Physiol. Biochem. 78, 27–36.
Sivritepe, N., Sivritepe, H.O., Eris, A., 2003. The effect of NaCl priming on salt tolerance
in melon seedlings grow under saline conditions. Sci. Hortic. 97, 229–237.
Smedema, L.K., Shiati, K., 2002. Irrigation and salinity: a perspectivereview of the salinity
hazards of irrigation development in the arid zone. Irrigat. Drain. Syst. 16 (2),161–174.
Steppuhn, H., van Genuchten, M.Th., Grieve, C.M., 2005. Root-zone salinity: I. Selecting a
product – yield index and response function for crop tolerance. Crop Sci. 45,
209–220.
Subramanyam, K., Laing, G.D., Van Damme, E.J.M., 2019. Sodium selenate treatmentusing a combination of seed priming and foliar spray alleviates salinity stress in rice.
Front. Plant Sci. 10, 1–17.
Tahjib-Ul-Arif, M., Roy, P.R., Sohag, A.A.M., Afrin, S., Rady, M.M., Hossain, M.A., 2018.
Exogenous calcium supplementation improves salinity tolerance in BRRI Dhan28; asalt susceptible high-yielding Oryza sativa cultivar. J. Crop Sci. Biotech. 21 (4),383–394.
Taie, H.A.A., Abdelhamid, M.T., Dawood, M.G., Nassar, R.M.A., 2013. Pre-sowing seedtreatment with proline improves some physiological, biochemical and anatomical
attributes of faba bean plants under sea water. J. Appl. Sci. Res. 9 (4), 2853–2867.
Takemura, Y., Satoh, M., Satoh, K., Hamada, H., Sekido, Y., Kubota, S., 2010. High dose of
ascorbic acid induces cell death in mesothelioma cells. Biochem. Biophys. Res.
Commun. 394 (2), 249–253.
Torabi, F., Majd, A., Enteshari, S., 2012. Effect of exogenous silicon on germination andseedling establishment in Borago Officinalis L. J. Med. Plant Res. 6 (10), 1896–1901.
Tuna, A.L., Kaya, C., Higgs, D., Murillo-Amador, B., Aydemir, S., Girgin, A.R., 2008.
Silicon improves salinity tolerance in wheat plants. Environ. Exp. Bot. 62, 10–16.
van Genuchten, M.Th., Gupta, S.K., 1993. A reassessment of the crop response function. J.
Indian Soc. Soil Sci. 41, 730–737.
van Genuchten, M.Th., Hoffman, G.J., 1984. Management aspect for crop production. In:
Shainberg, I., Shalhevet, J. (Eds.), Soil Salinity Under Irrigation. Springer, New York,
pp. 258–271.
van Genuchten, M.Th., 1983. Analyzing Crop Salt Tolerance Data: Model Description andUser’s Manual. Research Report No. 120, U.S. Salinity Laboratory, USDA-ARS, 50
pp. Riverside, CA.
Wang, W.B., Kim, Y.H., Lee, H.S., Kim, K.Y., Deng, X.P., Kwak, S.S., 2009. Analysis ofantioxidant enzyme activity during germination of alfalfa under salt and drought
stresses. Plant Physiol. Biochem. 47 (7), 570–577.

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