1. bookVolumen 32 (2020): Heft 2 (December 2020)
Zeitschriftendaten
License
Format
Zeitschrift
eISSN
2083-5965
Erstveröffentlichung
01 Jan 1989
Erscheinungsweise
2 Hefte pro Jahr
Sprachen
Englisch
access type Uneingeschränkter Zugang

Functional traits of okra cultivars (Chinese green and Chinese red) under salt stress

Online veröffentlicht: 07 Sep 2020
Volumen & Heft: Volumen 32 (2020) - Heft 2 (December 2020)
Seitenbereich: 159 - 170
Eingereicht: 07 Feb 2020
Akzeptiert: 31 Jul 2020
Zeitschriftendaten
License
Format
Zeitschrift
eISSN
2083-5965
Erstveröffentlichung
01 Jan 1989
Erscheinungsweise
2 Hefte pro Jahr
Sprachen
Englisch
Abstract

Two okra cultivars (Chinese green and Chinese red) were subjected to salt stress for 12 weeks. Salt stress treatments T1 (20.8 mM), T2 (103.3 mM), T3 (180.0 mM) and T4 (257.0 mM) were applied with equal proportions of NaCl and CaCl2 in Hoagland nutrient solution. Salt stress significantly affects photosynthesis, transpiration, stomatal conductance, water use efficiency, water potential, plant height, root length, fresh weight and dry weight of both okra cultivars in every salt stress treatment. At T2, T3 and T4, Chinese red plants maintained their physiological and growth traits up to Weeks 9, 6 and 3, respectively; beyond these salt-stress durations, growth reductions were found. Similarly, Chinese green plants maintained their growth up to Weeks 9, 5 and 3, respectively, at T2, T3 and T4 treatments. In comparison, Chinese red showed more tolerance than Chinese green. According to the results, the third and ninth weeks are the tolerance threshold limits for both cultivars to sustain their physiological traits and growth under T4 and T2 salinity treatments. Similarly, Chinese red has the threshold limit to bear T3 treatment up to the eighth week and Chinese green, up to the fifth week. Thus, this study provides a new method to determine the threshold value of crops with respect to duration under salt stress. This finding would be useful in the field of water saving and utilisation of saline water resources.

INTRODUCTION

Salt stress is one of the major environmental factors responsible for huge losses in the productivity of agricultural lands all over the world (Qiu et al., 2017). Salinity affects almost 70 million hectares of agricultural fields, and this area is expected to increase due to global changes and different irrigation activities (Zamani et al., 2017). The world's total cultivated land is classified into sodic (~38%) and saline land (24.3%), which are increasing day by day due to water scarcity (Qados, 2011). Consequently, agricultural production could be reduced by up to 32% by 2025, compared to the current year (i.e. 2020), due to water scarcity, salinity and loss of fertility. Approximately 33% of the world agricultural land is saline (Azeem et al., 2017b). The impact of salinity has been very high in the northern and coastal parts of China. Accordingly, one-third of the irrigated cropland of China faces salinity problem (Hou et al., 2007). Water scarcity and shortage of agricultural land give motivation to utilise saline water resources for production of different crops.

Salt stress affects plant growth in three different ways: (i) increase in osmotic potential of the soil solution, (ii) ionic imbalance and (iii) ionic toxicity (Munns et al., 2012). Reduction in crop production is directly related to the amount of salts present in the soluble solution (Tavakkoli et al., 2011). Salt stress can influence plant growth through physiological and morphological processes, including photosynthesis, stomatal conductance, transpiration, plant water status and growth (Wang et al., 2012; Maqbool et al., 2016; Zamani et al., 2017). The presence of salts in the nutrient solution or soil decreases water availability for the plant (Dang et al., 2008) due to a rise in the osmotic potential (Taïbi et al., 2016). In some cases, the stomata close to maintain the leaf's water status by reducing transpiration. This mechanism leads to reduced CO2 assimilation rate (Parida and Das, 2004), which affects the photosynthesis process and rate of plant growth (Azeem et al., 2017b). Some plants tolerate salt stress, but a further increase in salt stress exceeding the critical threshold value causes decreases in plant growth and other physiological attributes (Maas and Hoffman, 1977).

Previous studies have reported the tolerance ability of several crops using different methods, such as growing halophyte crops under saline water (Belkheiri and Mulas, 2013). Other reports have removed salts from the root zone with the help of scraping, flushing and leaching (Jouyban, 2012). Some papers have evaluated the response of crops and vegetables to different concentrations of saline water and reported a higher production under slight and moderate concentrations of salts (Riccardi et al., 2014; Elshaikh et al., 2018). Furthermore, a number of researchers have reduced the effects of saline irrigation by applying the method of re-watering or by using diluted water after 1 week to a maximum of 3 weeks without considering the duration of the effects on plants (Azeem et al., 2017a, 2017b; Javed et al., 2017, 2018). However, no reports are related to the plant survival ability or threshold values with respect to salt duration.

Okra (Abelmoschus esculentus L.) is an important vegetable crop, widely grown in the tropics, subtropics and Mediterranean regions (Saleem et al., 2011). Okra contains nutrients that are important to human health, including vitamins, potassium, calcium, carbohydrates and unsaturated fatty acids such as linolenic and oleic acids (Asare et al., 2016). It is classified as a moderately salt-tolerant vegetable crop (Maas and Hoffman, 1977), although it has been found that salt stress reduces okra yield (Shahid et al., 2011). Furthermore, many research works have been conducted on seed germination, as well as the morphological and physiological traits, of different okra cultivars under short durations of salt stress (Azeem et al., 2017a, 2017b). However, scarce information is available in literature on how far different physiological attributes in okra are regulated by long durations of salt stress. Thus, the aim of this study was (i) to evaluate the physiological trait response of two okra cultivars under different salt stress levels, (ii) to figure out the best threshold values and (iii) to estimate the relationship between duration of salt stress and plant survival.

MATERIALS AND METHODS
Plant material and culture conditions

This experiment was conducted in a greenhouse at Jiangsu University, Zhenjiang, Jiangsu, China (32.20ºN, 119.45ºE) from April to June 2017. Okra (Abelmoschus esculentus L.) was studied in a greenhouse maintained at a temperature of 28/22 ± 5ºC day/night, 60% relative humidity and 16 h photoperiod throughout the experimental period. Seeds of two okra cultivars, namely Chinese green (var. Blondy) and red (var. Red Velvet) were bought from the open market and were germinated in seedling trays containing a vermiculite, perlite and peat moss mixture with the ratio 1:1:1 (v/v/v). Germination trays were placed in an incubator with the controlled temperature of 25 ± 5ºC during day and night. Relative humidity was 60%, and artificial light was installed on the roof of the incubator, operating 12 h over the day time. During the germination stage, the seeds were watered daily with full strength of Hoagland solution (Hoagland and Arnon, 1950). After 2 weeks, when the seedlings had grown enough, we transferred them into plastic pots having four drain holes at the bottom with 9 cm inner diameter and 12 cm height containing vermiculite as a growing medium. These plants in pots were placed under a small tub, where they received 1 L of nutrient solution of every treatment. On every alternating day, we drained all the remaining nutrient treatment solution in the tub to avoid salt accumulation and added new solution of every treatment. Four treatments of saline irrigation were made, adding 1:1 ratio of NaCl and CaCl2 into full-strength Hoagland solution to get the following treatments: T1 (20.8 mM), T2 (103.3 mM), T3 (180.0 mM) and T4 (257.0 mM) (Table 1).

Different treatment levels

TreatmentConcentration (mM)Amount of NaCl in 1 L Hoagland culture medium (g · L−1)Amount of CaCl2 in 1 L Hoagland culture medium (g · L−1)
T120.800
T2103.333
T3180.066
T4257.099

The experiment was arranged in a complete randomised block design with four replicates of each treatment for every week, with 384 pots (4 × 2 × 4 × 12). One week after transplanting, every plant was treated with the corresponding saline water treatment; plants were exposed to saline irrigation for 12 weeks. After the end of every week, the plants in each treatment were randomly selected to measure the gas exchange and growth parameters with four replicates. After measuring these parameters, the plants were harvested by removing all vermiculate particles very carefully with the help of water to avoid root and shoot damage. Subsequently, the root length was measured with a measuring scale; then, the fresh weight of the plant was measured using a weighing balance. These plants were oven-dried at ≤80°C for 48 h (Azeem et al., 2020) to measure the dry weight.

Measurements and estimations
Gas exchange parameters

Gas exchange parameters, including photosynthesis (PN), stomatal conductance (Gs) and transpiration (E), were recorded using a portable LI-6400XT photosynthesis measurement system (LI-COR Biosciences, Lincoln, NE, USA). A fully extended leaf from the top of the plant was selected for measurement. Measurements were performed under full sunshine conditions from 10 am to 11 am.

Water use efficiency (WUE) was calculated according to the following equation: WUE=PN/E{\rm{WUE}} = {{\rm{P}}_{\rm{N}}}/{\rm{E}} where PN is the photosynthesis and E is the transpiration.

Water potential

The sampled leaf used to measure photosynthesis was used to determine the water potential (Wp) also on a weekly basis. Measurements were performed under full sunshine conditions from 10 am to 11 am. The leaf's water potential was measured with a dew point microvoltmeter (Psypro; Wescor, Logan, UT, USA) in a C-52-SF universal sample room (Wescor).

Growth parameters

Plants’ shoot and root lengths were measured with a millimetric ruler after every week. The stem diameter was measured with Vernier callipers.

Statistical analysis

The statistical analysis of the data collected for the growth and gas exchange parameters was performed in different steps. Assumptions of parametric statistics were tested to verify normality and homogeneity of variance using the Shapiro–Wilk normality test and the Levene test before further analysis. Two-way analysis of variance (ANOVA) was performed between salinity levels and salt duration, and the means of the results were compared by using the Tukey test at 95% probability levels. Then, three-way ANOVA was used to compute the differences in the measured response variables among cultivars, salinity levels, salt durations (weeks) and their interaction effects. Partial correlation was used to determine the relationship among salinity, salt duration and physiological traits. All statistical analyses were performed using SPSS 22, and graphs were drawn on OriginPro 9.0.

RESULTS AND DISCUSSION
Physiological traits

All physiological parameters of both cultivars (Chinese green and Chinese red) were significantly different among cultivars, salinity levels, salt durations and their interactions (Table 2). We found that PN of both Chinese green and Chinese red decreased significantly in every salinity level; the reduction was increasingly evident in every level of salinity with increase in the duration of salinity (Figure 1). At T2, the PN of both cultivars was non-significant at Weeks 1–4 than in Weeks 5–8. With the T3 treatment, both cultivars showed different results according to their tolerance ability; Chinese green maintained non-significant PN from Week 1 to Week 5 than in Weeks 6–8, and the remaining 4 weeks also yielded non-significant results. The same trend was shown by Chinese red for the first 5 weeks, but at Weeks 6–12, the PN was maintained, showing more tolerance than Chinese green (Figure 1). Both cultivars tolerated T4 salinity till the third week; after that, the plants were under severe stress and could not maintain reasonable PN value. The interaction effect of salt durations and cultivars was non-significant because the plants’ maintenance of PN continued for 3–4 weeks (Table 2 and Figure 1).

Variance analysis of physiological traits of two Okra cultivars under salt stress treatments

Main variablesCultSLevSDurCult × SLevCult × SDurSLev × SDurCult × SLev × SDur
PN33.72**7382.7**72.59**63.58**1.49NS118.81**2.17**
Gs14.60**2249.22**20.03**6.81**2.35**12.75**2.92**
E92.59**77.75**19.10**13.08**3.51**7.42**4.51**
WUE54.83**646.96**15.71**2.45NS2.98**21.35**3.32**
Wp46.30**1332.00**71.77**18.81**1.52NS12.43**1.24NS

Significant difference at p < 0.01.

NS represents non-significant difference.

Cult, cultivars; SLev, salinity levels; SDur, salt duration; PN, photosynthesis; Gs, stomatal conductance; E, transpiration; WUE, water use efficiency; Wp, water potential.

Figure 1

Effects of salinity treatments on the photosynthesis (A,B), stomatal conductance (C,D) and transpiration (E,F) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests.

Stomatal conductance (Gs) of both cultivars was significantly different among salinity levels, cultivars, salt durations and their interactions (Table 2). The trend of Gs for both cultivars was the same as for PN. The Gs was reduced more with increase of salinity level and salt duration (Figure 1). Chinese green, at T2, maintained the Gs from Week 1 to Week 6, which then decreased from Week 7 to Week 12. At T3, the Gs level was maintained between Week 1 and Week 3, then decreasing at the fourth week compared with the first week. At T4, after Week 2, the Gs level decreased greatly, showing that the plants were under severe salt stress and found it difficult to survive. For this variable, the Chinese red cultivar showed a different response from that of Chinese green due to its tolerance ability. The Gs was reduced at T2 salinity, but differences were non-significant throughout the whole salt stress period under T2. A non-significant reduction in Gs was observed at T3 salinity, during the period between Week 1 and Week 8, but after this period, a significant reduction was detected. After Week 3, the Gs under T4 decreased drastically, showing a severe salt stress effect on the plants (Figure 1).

Significant differences in the transpiration (E) of both cultivars were detected among salinity treatments, salt durations, cultivars and their interactions (Table 2). The value of E of both cultivars under different salinity levels decreased with longer salt stress durations (Figure 1). These decreasing E values indicated that at the beginning of salt stress, the plants tried to withstand that stress and maintained a constant rate, but when the salt stress duration became longer, the plant's tolerance ability was affected and the E value increased (Figure 1). Chinese green showed increasing E after Weeks 8, 5 and 4 at salinity levels T2, T3 and T4, respectively. Chinese red reflected increases in E after Weeks 10, 6 and 3 at salinity levels T2, T3 and T4, respectively. At the same stage, the value of E increased in both cultivars after Week 8 in every salinity level, suggesting that both cultivars were under high salt stress, losing their ability to use the water for their development, with consequent water losses due to continuous transpiration.

Significant differences in water use efficiency (WUE) were detected between cultivars, salt durations, salinity treatments and their interactions (Table 2). Nevertheless, salinity treatments and cultivar interactions were non-significant. The WUE was calculated with the help of PN and E; so, according to these parameter results, the WUE was also affected with respect to salt durations and salinity levels. At T2, T3 and T4, Chinese green WUE increased at Weeks 7, 5 and 4; subsequently, the WUE was decreasing because at that stage, the value of E was increasing. The WUE of Chinese red also decreased with longer duration of salt stress, but Chinese red showed more tolerance compared with Chinese green. At T4, T3 and T2 salinity levels, the WUE of Chinese red decreased at Weeks 9, 5 and 4. When the WUE started to decrease, the results were similar and non-significant for both cultivars; such condition reflected the clear tendency of being under a severe stress (Figure 2).

Figure 2

Effects of the salinity treatments on the WUE (G,H) and water potential (I,J) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests. WUE represents water use efficiency.

The water potential (Wp) was significantly different between cultivars, salinity treatments, salt durations and their interactions (Table 2). The Wp of both cultivars between salt stress durations and salinity levels was significantly decreased (Figure 2). At T2, T3 and T4, the Wp values were non-significantly increased in Weeks 8, 6 and 2, respectively. After this period, the results were also non-significant in the remaining weeks, indicating that at the first stage, the plants bear these stresses and maintain good water status in the plant leaf, which helps the plant to develop in growth (Figure 2). Thereafter, the plants lose their withstanding ability and continue to lose water in the form of E, and only salts are present in the plant leaf tissue, which shows decreasing water potential. Similar results were shown by Chinese red and Chinese green under these salinity levels, but Chinese red tried to bear these salinity treatments 1 week longer in every treatment level compared with Chinese green.

Growth traits

The main effects of cultivars, salinity treatments, salt durations and their interactions were significant in terms of most of the growth parameters (Table 3). Plant height (PH) increased smoothly under the control condition for both cultivars (Tables 5 and 6). Salinity levels and salt durations affected growth differently in both cultivars. At T2, the PH of Chinese green increased significantly from Week 1 to Week 8, and after 8 weeks, the PH was non-significant. Chinese green showed the same trend: at T3 and T4, the PH increased significantly from Week 1 to Weeks 5 and 3, respectively, and, thereafter, stayed non-significant for the remaining duration of salt stress. At T2, the PH increased significantly every week, indicating that Chinese red can bear the salt stress level even with significant reduction in growth, as compared to the control (T1). At T3 and T4, the PH was increased significantly from Week 1 to Weeks 5 and 4, respectively. Subsequently, there was a non-significant increase in the PH for the remainder of the salt stress duration (Table 6).

Variance analysis of growth traits of two okra cultivars under salt stress

Main variablesCultSLevSDurCult × SLevCult × SDurSLev × SDurCult × SLev × SDur
PH87.227**16630.85**4912.286**8.318**18.801**1008.619**18.078**
RL94.138**6422.472**1603.98**258.563**10.662**300.922**13.369**
SD1.822NS3940.037**655.581**64.922**0.294NS206.851**2.058**
FW34.992**4948.99**662.663**40.121**4.575**208.645**7.73**
DW13.041**1916.822**249.977**5.433**1.289NS75.574**0.874NS

Significant difference at p < 0.01.

NS represents non-significant difference.

Cult, cultivars; SLev, salinity levels; SDur, salt duration; PH, plant height; RL, root length; SD, stem diameter; FW, fresh weight; DW, dry weight.

Correlation between different parameters of two okra cultivars

SDRLFWDWPNGsEWUEWpSDurSLev
Green
PH0.952**0.969**0.950**0.934**0.693**0.549**0.350**0.544**0.392**0.593**–0.578**
SD0.978**0.982**0.956**0.768**0.667**0.368**0.605**0.496**0.497**–0.640**
RL0.976**0.957**0.726**0.589**0.350**0.580**0.425**0.571**–0.601**
FW0.986**0.808**0.683**0.394**0.646**0.508**0.481**–0.663**
DW0.803**0.675**0.398**0.637**0.509**0.472**–0.660**
PN0.932**0.1540.907**0.839**0.017–0.840**
Gs0.1540.818**0.891**–0.115–0.845**
E–0.170*0.0240.393**–0.296**
WUE0.800**–0.115–0.758**
Wp–0.324**–0.859**
SDur0.000
Red
PH0.957**0.946**0.961**0.951**0.665**0.460**0.428**0.505**0.302**0.642**–0.572**
SD0.947**0.967**0.967**0.679**0.523**0.450**0.521**0.410**0.544**–0.623**
RL0.940**0.943**0.666**0.440**0.510**0.509**0.343**0.604**–0.644**
FW0.992**0.796**0.621**0.413**0.635**0.483**0.479**–0.680**
DW0.797**0.620**0.418**0.642**0.496**0.469**–0.694**
PN0.894**0.212*0.912**0.811**0.000–0.857**
Gs0.187*0.813**0.893**–0.221**–0.853**
E–0.1300.0740.465**–0.387**
WUE0.789**–0.141–0.766**
Wp–0.381**–0.817**
SDur0.000

Correlation is significant at the 0.05 level (two-tailed).

Correlation is significant at the 0.01 level (two-tailed).

SLev, salinity levels; SDur, salt duration; PH, plant height; SD, stem diameter; RL, root length; FW, fresh weight; DW, dry weight; PN, photosynthesis; Gs, stomatal conductance; E, transpiration; WUE, water use efficiency; Wp, water potential.

The stem diameters (SD) of both cultivars were significantly affected by cultivars, salinity treatments, salt durations and their interactions (Table 3). The SD values of both cultivars were decreased significantly as compared to the control (T1). The cultivars’ effect on SD was found to be non-significant, indicating that both cultivars behave the same under these salinity treatments. At T2 and T3 treatments, both cultivars showed significant increment in the SD from Week 1 to Weeks 8 and 5, respectively; thereafter, there was an increment but this was non-significant, indicating greater demonstration in plant growth. The SD for Chinese green significantly increased from Week 1 to Week 4 (Table 5) and, for Chinese red, from Week 1 to Week 3 (Table 6); subsequently, both cultivars showed non-significant increment.

Plant height, stem diameter and root length of Chinese green under different salinity treatments

SLevSalt duration (weeks)
123456789101112
Plant height, cmT114.2 a23.8 b30.4 c36.3 d43.7 e49.9 f57.3 g64.2 h76.7 i83.5 j103.0 k117.6 l
T213.1 f18.1 h21.9 c31.3 g35.6 e44.9 f48.0 f52.2 g52.4 g52.14 g52.4 g52.3 g
T312.3 a17.8 b23.8 f27.8 d32.6 e32.4 e32.6 e32.3 e32.5 e32.5 e32.4 e32.6 e
T411.9 a18.9 c26.4 b26.5 b26.5 b26.5 b26.5 b26.5 b26.3 b26.4 b26.3 b26.4 b
Stem diameter, cmT13.6 a4.1 a4.4 ab5.4 ab7.8 bc10.7 bc13.6 cd16.9 d19.7 d21.3 e22.1 e23.0 e
T22.4 b2.8 c3.8 a4.4 d5.13 e5.3 f5.9 g8.3 g8.5 g8.5 g8.51 g9.0 g
T32.2 d2.8 b3.7 b3.8 a5.6 g5.7 g5.6 g5.8 g5.6 g5.4 g5.6 g5.6 g
T41.9 e2.4 f2.8 g3.1 h3.1 h3.1 h3.1 h3.1 h3.2 h3.1 h3.08 h3.1 h
Root length, cmT19.8 a12.0 b14.1 c15.2 d17.5 e20.4 f25.9 g29.9 h33.1 i33.6 ij34.1 j35.1 k
T29.6 a9.8 bc10.8 b13.4 e14.9 d17.3 g19.3 f20.8 j20.6 j20.7 j20.8 j20.7 j
T39.7 c11.7 a12.7 d13.4 b14.2 h15.2 i15.3 i15.3 i15.3 i15.3 i15.2 i15.3 i
T49.4 d11.2 c12.1 b12.5 b12.6 b12.7 b12.6 b12.6 b12.6 b12.6 b12.6 b12.3 b

Values represent means, followed by different letters in the same treatment process indicating a significant difference at p ≤ 0.05, according to Tukey tests. T1 = 20.8 mM; T2 = 103.3 mM; T3 = 180.0 mM; and T4 = 257.0 mM.

SLev, salinity levels.

Plant height, stem diameter and root length of Chinese red under different salinity treatments

SLevSalt duration (weeks)
123456789101112
Plant height, cmT114.9 a20.2 b30.0 c40.0 d45.0 e53.3 f66.0 g71.0 h82.0 i87.6 j97.6 k110.6 l
T213.9 i16.7 k22.8 j29.2 i33.7 h38.4 g45.6 f47.5 e56.0 d57.1 c57.2 b57.2 a
T313.2 c18.3 d21.8 e25.3 f35.0 g36.4 g36.1 g36.3 g36.1 g36.2 g36.2 g36.1 g
T48.4 b17.3 c23.7 d28.6 e28.7 e28.5 e28.6 e28.3 e28.7 e28.6 e28.6 e28.4 e
Stem diameter, cmT13.6 a3.8 a4.4 a5.1 ab6.8 b9.1 bc11.6 c15.0 d17.2 de18.9 e20.6 e21.6 e
T22.6 b2.8 b3.9 c4.3 d4.9 e5.2 e5.8 f7.8 g9.1 g9.2 g9.14 g9.2 g
T32.4 c2.8 d3.5 e5.1 f7.5 g7.5 g7.1 g7.1 g7.2 g7.2 g7.2 g7.2 g
T41.7 d2.2 e2.6 f2.5 f2.2 f2.1 f2.7 f2.6 f2.6 f2.7 f2.6 f2.6 f
Root length, cmT110.2 a11.4 ab14.3 b18.4 c20.4 cd23.6 d26.1 de28.4 e30.1 ef31.2 ef32.3 f32.3 f
T29.5 b11.7 c13.2 d15.1 e17.2 f8.1 f20.4 g21.6 gh22.9 h23.6 h23.7 h23.7 h
T38.9 c10.6 d14.7 e15.4 f18.8 g18.7 g18.6 g18.6 g18.6 g18.5 g18.5 g18.6 g
T48.5 d9.1 e10.5 f11.3 k11.3 k11.3 k11.6 k11.3 k11.1 k11.3 k11.2 k11.3 k

Values represent means, followed by different letters in the same treatment process indicating a significant difference at p ≤ 0.05, according to Tukey tests. T1 = 20.8 mM; T2 = 103.3 mM; T3 = 180.0 mM; and T4 = 257.0 mM.

SLev, salinity levels.

The root is the main part for plant growth because it gets connected first with the salt water; it then transfers water to the stem of the plant. The root lengths (RLs) of both cultivars were affected significantly by salinity treatments, salt durations, cultivars and their interactions (Table 3). The RL significantly decreased in all salinity treatments of both cultivars (Tables 5 and 6). The RLs of Chinese green at T2, T3 and T4 increased significantly from Week 1 to Weeks 8, 6 and 3, respectively. The RL of Chinese red, at T2, T3 and T4, increased significantly from Week 1 to Weeks 8, 5 and 3, respectively.

The fresh weight (FW) traits differed significantly among salinity treatments, salt durations, cultivars and their interactions (Table 3). The FWs of both cultivars were decreasing every week with respect to the control (Figure 3). In the seventh week, >50% reduction was found for Chinese green with treatment levels T2 and T3 compared with the control. For individual levels, the T2 FW was increasing slowly throughout the whole salt duration period. At treatment levels T2 and T3, the FW of Chinese green increased significantly from Week 1 to Weeks 7 and 5, respectively. After that, the FW under these treatments decreased significantly until the harvest (Figure 3). Chinese red also showed reduction in FW in every treatment when plotted against salt duration as compared to the control treatment.

Figure 3

Effects of salinity treatments on the fresh weight (Q,R) and dry weight (S,T) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests.

Chinese red showed a similar trend as Chinese green with the salinity level T2. At T3 salinity level, the Chinese red FW increased significantly between the first and the fourth weeks. Thereafter, during Weeks 4–8, the increment was non-significant; in the remaining 4 weeks, constant FW was found, showing the tolerance ability of Chinese red. At T4, the FW increased tremendously from Week 1 to Week 4; then, the FW decreased throughout the remaining salt duration period, which implies that the plant was under severe salt stress, losing its original weight, with eventual lethality.

The dry weight (DW) of both cultivars was significantly changed with respect to individual factors, but their interactions were non-significant (Table 3). Both cultivars showed reduced DW at every salinity level, as compared to the control (T1). At T2, both cultivars’ DW increased significantly between these levels throughout the salt duration period. At T4 level, both cultivars’ DW decreased after 4 weeks of treatment and continued to decrease until the harvest. At T3, Chinese green DW increased from Week 1 to Week 7, and Chinese red DW increased from Week 1 to Week 11 significantly, which also indicated that Chinese green is sensitive in nature and Chinese red has the ability to bear higher stresses for long durations.

Correlations between different parameters of both okra cultivars

The partial correlation coefficients for the relationship between different parameters of both okra cultivars are shown in Table 4. In both cultivars, a significant positive correlation between gas exchange parameters and growth parameters on the one hand and a negative correlation with the salinity treatment levels on the other hand were observed. The duration of the salt stress period reflected a positive significant correlation with the growth parameters in both cultivars, but it was negatively correlated with Wp and WUE. The negative correlation between water status parameters and salt duration explains that continually receiving higher salts in the nutrient solution over a long duration causes osmotic pressure, which creates a negative impact on plant water status.

Physiological and growth traits under salt stress

Screening of crops against salt stress treatments is considered of high potential value under the water-saving irrigation perspective (Munns et al., 2012). The studied cultivars reflected a high variation in salt tolerance, according to their physiological and growth-related responses to salt stress and duration of the salt stresses.

Photosynthesis, known as one of the most complex and fundamental physiological processes, could be severely affected by salt stress in several crops (Qiu et al., 2017; Allel et al., 2018). A large variation in PN was observed in our study with respect to the salinity levels, salt durations and their interactions (Table 2). It seems that the photosynthetic apparatus of both okra cultivars could tolerate all salt stress treatments for different salt durations (Figure 1). Both cultivars tolerated salt stress at T4 for only the first 3 weeks; afterwards, a continued decrease of gas exchange activities was observed but it was also tolerated. At T2 and T3, the Chinese red cultivar tolerated salt stress from Week 1 to Week 8 or 9, respectively, and Chinese green, from Week 1 to Week 5 or 6, respectively, maintaining adequate gas exchange parameters (Figure 1). Saline irrigation may limit the PN activity by a reduction of CO2 supply, arising from a partial closure of stomata or by altering the biochemical CO2 fixation mechanism or by both procedures at once (Senguttuvel et al., 2014). The reduction in CO2 availability due to the limitation of stomatal diffusion is considered as the starting effect of salt stress on PN, which is caused either by a decline of guard cell turgidity or by abscisic acid accumulation, mediating stomatal closure (Chaves et al., 2009). We found high variability in salt tolerance of okra cultivars in terms of stomatal conductance depending on salt stress levels and their durations. Accordingly, we conclude that the change in PN appeared to be associated with stomatal conductance. The state of the stomatal aperture is a compromise between water loss and assimilation of atmospheric CO2. In this study, stomatal closure was a response to reduce water loss through transpiration, trying to maintain an adequate water status within plant cells and maintaining reasonable WUE. At T2 and T3 levels, Chinese green and Chinese red maintained WUE from Week 1 to Week 9 or 8, respectively, and Week 4 or 5, respectively. Afterwards, the value of E increased and PN decreased, which affect the WUE because WUE has a strong relationship with them (Table 4). Increase in E indicated that the plant was under severe salt stress and was not able to maintain its growth due to continuous water loss (Allel et al., 2018).

At the beginning of the salt stress period, both cultivars significantly reduced their growth rate with respect to the control (T1), but afterwards, they sustained and developed a significant growth rate (Tables 5 and 6). This showed that both cultivars have tolerance ability to bear these salt stresses for some duration (Adem et al., 2014). Chinese red was the most successful cultivar, giving significant production under T2 for 1–9 weeks and, at T3, for 1–5 weeks; after that, the increment in the growth was non-significant with respect to the previous week. On the other hand, Chinese green showed significant changes in plant growth at T2 from Week 1 to Week 8, and at T3, from Week 1 to Week 4; thereafter, the growth parameters did not show sufficient increase, and at this stage, the plants were under their threshold limit of bearing salt stresses (Javed et al., 2017). The presentation of plant growth is linked with plant water status because continuous use of saline irrigation increases the salt concentrations in the root zone, thus decreasing soil water potential (Javed et al., 2019a). Under these conditions, dehydration occurs at the cellular level, which ultimately causes osmotic stresses (Javed et al., 2019b). These osmotic stresses produce ionic imbalance by increasing the amounts of Na+ and Cl and decreasing the amounts of K+, Ca2+ and Mn2+ (Chen et al., 2016). When these toxic salts reach the leaf, turgor loss and the death of leaf cells and tissues happen (Azeem et al., 2017a).

Physiological and growth trait relationship under salt stress

A strong relationship was found between the gas exchange parameters and plant growth under salt stress conditions. The interaction effect of salinity levels and their durations significant affected PN, Gs and E in every salinity treatment, due to which plant growth was reduced, as shown in Tables 2 and 3. The reduction in gas exchange parameters was due to the increase in salt concentration in the nutrient solution, creating osmotic potential within the soil and the plant, which causes loss in the ability of the plant to get water as it normally does from a non-saline solution (Shahid et al., 2011). The increasing concentration of salt in the nutrient solution creates a negative effect on plant water status by reducing WUE and Wp (Xing et al., 2018), which causes higher solute concentration in the leaf cytosol (Zhang et al., 2015). Under these conditions, plants try to save water by means of stomatal closure. Then, E decreases due to stomatal closure, forcing the plant to maintain a reasonable PN only for a short time, because CO2 assimilation is disturbed because of stomatal closure (Javed et al., 2017; Qiu et al., 2017). This response was detected in both Chinese red and Chinese green at T2, T3 and T4, which maintained the gas exchange and growth parameters under these different salinity treatments from Week 1 to Weeks 9, 5 and 3. After these periods, both cultivars reflected non-significant changes in behaviour in terms of physiological and growth variables, due to which the fresh weight of both cultivars clearly decreased (Figure 3). This suggested that plants cannot withstand these stresses for longer duration because their cells are lethally damaged (Brodribb et al., 2005). It may suggest that Weeks 3 and 9 are the tolerance threshold limits for both cultivars to sustain their gas exchange activities and growth under T4 and T2 salinity treatments, respectively. Similarly, at T3, the threshold limit for bearing this salinity treatment in the case of Chinese red was Week 8 and, Chinese green, Week 5. At these threshold durations, both cultivars needed to reduce salt concentrations for their survival (Javed et al., 2018). In all previous studies, the researchers overcame the salt stress effect with different techniques and methods, such as using halophyte crops (Belkheiri and Mulas, 2013) and by removing salt in the root zone by scraping, flushing and leaching (Jouyban, 2012). Some of them gave fresh water while re-watering (Javed et al., 2018), and many used biochar in the soil to overcome salinity effects (She et al., 2018; Huang et al., 2019). According to the response of both cultivars, we suggest using dilute water for re-watering, i.e. T4 salinity treatment would receive water of T3 on the suggested threshold week; similarly, for T3 and T2 treatments.

CONCLUSIONS

Both okra cultivars were found to be salt tolerant under different salt concentrations. Physiological and growth parameters played an important role to sustain their growth under saline irrigation. At T2, T3 and T4, Chinese green maintained its physiological traits and growth increment was noted up to Weeks 9, 5 and 3, respectively. Similarly, in the case of Chinese red, under these salinity treatments, such increment was noted up to Weeks 9, 6 and 3, respectively. According to the results, it is concluded that the above-mentioned weeks could be considered as the threshold limits of both okra cultivars to bear these salinity levels with respect to salt durations. When the plants reach their threshold limits, then dilution of salts or re-watering will be needed to overcome the effect of salt stress on the plants. The finding of this study will help to save pure water and utilise saline water resources for the production of different crops.

Figure 1

Effects of salinity treatments on the photosynthesis (A,B), stomatal conductance (C,D) and transpiration (E,F) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests.
Effects of salinity treatments on the photosynthesis (A,B), stomatal conductance (C,D) and transpiration (E,F) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests.

Figure 2

Effects of the salinity treatments on the WUE (G,H) and water potential (I,J) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests. WUE represents water use efficiency.
Effects of the salinity treatments on the WUE (G,H) and water potential (I,J) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests. WUE represents water use efficiency.

Figure 3

Effects of salinity treatments on the fresh weight (Q,R) and dry weight (S,T) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests.
Effects of salinity treatments on the fresh weight (Q,R) and dry weight (S,T) of Chinese green and Chinese red, respectively; values represent means ± standard errors, followed by different letters in the same treatment process indicating a significant difference at p < 0.05, according to Tukey tests.

Plant height, stem diameter and root length of Chinese red under different salinity treatments

SLevSalt duration (weeks)
123456789101112
Plant height, cmT114.9 a20.2 b30.0 c40.0 d45.0 e53.3 f66.0 g71.0 h82.0 i87.6 j97.6 k110.6 l
T213.9 i16.7 k22.8 j29.2 i33.7 h38.4 g45.6 f47.5 e56.0 d57.1 c57.2 b57.2 a
T313.2 c18.3 d21.8 e25.3 f35.0 g36.4 g36.1 g36.3 g36.1 g36.2 g36.2 g36.1 g
T48.4 b17.3 c23.7 d28.6 e28.7 e28.5 e28.6 e28.3 e28.7 e28.6 e28.6 e28.4 e
Stem diameter, cmT13.6 a3.8 a4.4 a5.1 ab6.8 b9.1 bc11.6 c15.0 d17.2 de18.9 e20.6 e21.6 e
T22.6 b2.8 b3.9 c4.3 d4.9 e5.2 e5.8 f7.8 g9.1 g9.2 g9.14 g9.2 g
T32.4 c2.8 d3.5 e5.1 f7.5 g7.5 g7.1 g7.1 g7.2 g7.2 g7.2 g7.2 g
T41.7 d2.2 e2.6 f2.5 f2.2 f2.1 f2.7 f2.6 f2.6 f2.7 f2.6 f2.6 f
Root length, cmT110.2 a11.4 ab14.3 b18.4 c20.4 cd23.6 d26.1 de28.4 e30.1 ef31.2 ef32.3 f32.3 f
T29.5 b11.7 c13.2 d15.1 e17.2 f8.1 f20.4 g21.6 gh22.9 h23.6 h23.7 h23.7 h
T38.9 c10.6 d14.7 e15.4 f18.8 g18.7 g18.6 g18.6 g18.6 g18.5 g18.5 g18.6 g
T48.5 d9.1 e10.5 f11.3 k11.3 k11.3 k11.6 k11.3 k11.1 k11.3 k11.2 k11.3 k

Variance analysis of growth traits of two okra cultivars under salt stress

Main variablesCultSLevSDurCult × SLevCult × SDurSLev × SDurCult × SLev × SDur
PH87.227**16630.85**4912.286**8.318**18.801**1008.619**18.078**
RL94.138**6422.472**1603.98**258.563**10.662**300.922**13.369**
SD1.822NS3940.037**655.581**64.922**0.294NS206.851**2.058**
FW34.992**4948.99**662.663**40.121**4.575**208.645**7.73**
DW13.041**1916.822**249.977**5.433**1.289NS75.574**0.874NS

Correlation between different parameters of two okra cultivars

SDRLFWDWPNGsEWUEWpSDurSLev
Green
PH0.952**0.969**0.950**0.934**0.693**0.549**0.350**0.544**0.392**0.593**–0.578**
SD0.978**0.982**0.956**0.768**0.667**0.368**0.605**0.496**0.497**–0.640**
RL0.976**0.957**0.726**0.589**0.350**0.580**0.425**0.571**–0.601**
FW0.986**0.808**0.683**0.394**0.646**0.508**0.481**–0.663**
DW0.803**0.675**0.398**0.637**0.509**0.472**–0.660**
PN0.932**0.1540.907**0.839**0.017–0.840**
Gs0.1540.818**0.891**–0.115–0.845**
E–0.170*0.0240.393**–0.296**
WUE0.800**–0.115–0.758**
Wp–0.324**–0.859**
SDur0.000
Red
PH0.957**0.946**0.961**0.951**0.665**0.460**0.428**0.505**0.302**0.642**–0.572**
SD0.947**0.967**0.967**0.679**0.523**0.450**0.521**0.410**0.544**–0.623**
RL0.940**0.943**0.666**0.440**0.510**0.509**0.343**0.604**–0.644**
FW0.992**0.796**0.621**0.413**0.635**0.483**0.479**–0.680**
DW0.797**0.620**0.418**0.642**0.496**0.469**–0.694**
PN0.894**0.212*0.912**0.811**0.000–0.857**
Gs0.187*0.813**0.893**–0.221**–0.853**
E–0.1300.0740.465**–0.387**
WUE0.789**–0.141–0.766**
Wp–0.381**–0.817**
SDur0.000

Different treatment levels

TreatmentConcentration (mM)Amount of NaCl in 1 L Hoagland culture medium (g · L−1)Amount of CaCl2 in 1 L Hoagland culture medium (g · L−1)
T120.800
T2103.333
T3180.066
T4257.099

Variance analysis of physiological traits of two Okra cultivars under salt stress treatments

Main variablesCultSLevSDurCult × SLevCult × SDurSLev × SDurCult × SLev × SDur
PN33.72**7382.7**72.59**63.58**1.49NS118.81**2.17**
Gs14.60**2249.22**20.03**6.81**2.35**12.75**2.92**
E92.59**77.75**19.10**13.08**3.51**7.42**4.51**
WUE54.83**646.96**15.71**2.45NS2.98**21.35**3.32**
Wp46.30**1332.00**71.77**18.81**1.52NS12.43**1.24NS

Plant height, stem diameter and root length of Chinese green under different salinity treatments

SLevSalt duration (weeks)
123456789101112
Plant height, cmT114.2 a23.8 b30.4 c36.3 d43.7 e49.9 f57.3 g64.2 h76.7 i83.5 j103.0 k117.6 l
T213.1 f18.1 h21.9 c31.3 g35.6 e44.9 f48.0 f52.2 g52.4 g52.14 g52.4 g52.3 g
T312.3 a17.8 b23.8 f27.8 d32.6 e32.4 e32.6 e32.3 e32.5 e32.5 e32.4 e32.6 e
T411.9 a18.9 c26.4 b26.5 b26.5 b26.5 b26.5 b26.5 b26.3 b26.4 b26.3 b26.4 b
Stem diameter, cmT13.6 a4.1 a4.4 ab5.4 ab7.8 bc10.7 bc13.6 cd16.9 d19.7 d21.3 e22.1 e23.0 e
T22.4 b2.8 c3.8 a4.4 d5.13 e5.3 f5.9 g8.3 g8.5 g8.5 g8.51 g9.0 g
T32.2 d2.8 b3.7 b3.8 a5.6 g5.7 g5.6 g5.8 g5.6 g5.4 g5.6 g5.6 g
T41.9 e2.4 f2.8 g3.1 h3.1 h3.1 h3.1 h3.1 h3.2 h3.1 h3.08 h3.1 h
Root length, cmT19.8 a12.0 b14.1 c15.2 d17.5 e20.4 f25.9 g29.9 h33.1 i33.6 ij34.1 j35.1 k
T29.6 a9.8 bc10.8 b13.4 e14.9 d17.3 g19.3 f20.8 j20.6 j20.7 j20.8 j20.7 j
T39.7 c11.7 a12.7 d13.4 b14.2 h15.2 i15.3 i15.3 i15.3 i15.3 i15.2 i15.3 i
T49.4 d11.2 c12.1 b12.5 b12.6 b12.7 b12.6 b12.6 b12.6 b12.6 b12.6 b12.3 b

Adem, G. D., Roy, S. J., Zhou, M., Bowman, J. P. and Shabala, S. (2014). Evaluating contribution of ionic, osmotic and oxidative stress components towards salinity tolerance in barley. BMC Plant Biology, 14, 113.AdemG. D.RoyS. J.ZhouM.BowmanJ. P.ShabalaS.2014Evaluating contribution of ionic, osmotic and oxidative stress components towards salinity tolerance in barleyBMC Plant Biology1411310.1186/1471-2229-14-113402155024774965Search in Google Scholar

Allel, D., Ben-amar, A., and Abdelly, C. (2018). Leaf photosynthesis, chlorophyll fluorescence and ion content of barley (Hordeum vulgare) in response to salinity. Journal of Plant Nutrition, 41, 497–508.AllelD.Ben-amarA.AbdellyC.2018Leaf photosynthesis, chlorophyll fluorescence and ion content of barley (Hordeum vulgare) in response to salinityJournal of Plant Nutrition4149750810.1080/01904167.2017.1385811Search in Google Scholar

Asare, A. T., Asare-bediako, E., Agyarko, F., Taah, K., and Osei, E. O. (2016). Phenotypic traits detect genetic variability in Okra (Abelmoschus esculentus. L. Moench). African Journal of Agricultural Research, 11, 3169–3177.AsareA. T.Asare-bediakoE.AgyarkoF.TaahK.OseiE. O.2016Phenotypic traits detect genetic variability in Okra (Abelmoschus esculentus. L. Moench)African Journal of Agricultural Research113169317710.5897/AJAR2016.11160Search in Google Scholar

Azeem, A., Sun, J., Javed, Q., Jabran, K., and Du, D. (2020). The effect of submergence and eutrophication on the trait's performance of Wedelia trilobata over its congener native Wedelia chinensis. Water, 12, 934.AzeemA.SunJ.JavedQ.JabranK.DuD.2020The effect of submergence and eutrophication on the trait's performance of Wedelia trilobata over its congener native Wedelia chinensisWater1293410.3390/w12040934Search in Google Scholar

Azeem, A., Wu, Y., Javed, Q., Xing, D., Ullah, I., and Kumi, F. (2017a). Response of okra based on electrophysiological modeling under salt stress and re-watering. Bioscience Journal, 33(5), 1219–1229.AzeemA.WuY.JavedQ.XingD.UllahI.KumiF.2017aResponse of okra based on electrophysiological modeling under salt stress and re-wateringBioscience Journal3351219122910.14393/BJ-v33n5a2017-37178Search in Google Scholar

Azeem, A., Wu, Y., Xing, D., Javed, Q., and Ullah, I. (2017b). Photosynthetic response of two okra cultivars under salt stress and re-watering. Journal of Plant Interactions, 12, 67–77.AzeemA.WuY.XingD.JavedQ.UllahI.2017bPhotosynthetic response of two okra cultivars under salt stress and re-wateringJournal of Plant Interactions12677710.1080/17429145.2017.1279356Search in Google Scholar

Belkheiri, O., and Mulas, M. (2013). The effects of salt stress on growth, water relations and ion accumulation in two halophyte Atriplex species. Environmental and Experimental Botany, 86, 17–28.BelkheiriO.MulasM.2013The effects of salt stress on growth, water relations and ion accumulation in two halophyte Atriplex speciesEnvironmental and Experimental Botany86172810.1016/j.envexpbot.2011.07.001Search in Google Scholar

Brodribb, T. J., Holbrook, N. M., Zwieniecki, M. A., and Palma, B. (2005). Leaf hydraulic capacity in ferns, conifers and angiosperms: Impacts on photosynthetic maxima. New Phytologist, 165, 839–846.BrodribbT. J.HolbrookN. M.ZwienieckiM. A.PalmaB.2005Leaf hydraulic capacity in ferns, conifers and angiosperms: Impacts on photosynthetic maximaNew Phytologist16583984610.1111/j.1469-8137.2004.01259.x15720695Search in Google Scholar

Chaves, M., Flexas, J., and Pinheiro, C. (2009). Photosynthesis under drought and salt stress: Regulation mechanisms from whole plant to cell. Annals of Botany, 103, 551–560.ChavesM.FlexasJ.PinheiroC.2009Photosynthesis under drought and salt stress: Regulation mechanisms from whole plant to cellAnnals of Botany10355156010.1093/aob/mcn125270734518662937Search in Google Scholar

Chen, S., Zhang, Z., Wang, Z., Guo, X., Liu, M., Hamoud, Y. A., Zheng, J., and Qiu, R. (2016). Effects of uneven vertical distribution of soil salinity under a buried straw layer on the growth, fruit yield, and fruit quality of tomato plants. Scientia Horticulturae, 203, 131–142.ChenS.ZhangZ.WangZ.GuoX.LiuM.HamoudY. A.ZhengJ.QiuR.2016Effects of uneven vertical distribution of soil salinity under a buried straw layer on the growth, fruit yield, and fruit quality of tomato plantsScientia Horticulturae20313114210.1016/j.scienta.2016.03.024Search in Google Scholar

Dang, Y., Dalal, R., Mayer, D., Mcdonald, M., Routley, R., Schwenke, G., Buck, S., Daniells, I., Singh, D., and Manning, W. (2008). High subsoil chloride concentrations reduce soil water extraction and crop yield on Vertosols in north-eastern Australia. Australian Journal of Agricultural Research, 59, 321–330.DangY.DalalR.MayerD.McdonaldM.RoutleyR.SchwenkeG.BuckS.DaniellsI.SinghD.ManningW.2008High subsoil chloride concentrations reduce soil water extraction and crop yield on Vertosols in north-eastern AustraliaAustralian Journal of Agricultural Research5932133010.1071/AR07192Search in Google Scholar

Elshaikh, N. A., Zhipeng, L., Dongli, S., and Timm, L. C. (2018). Increasing the okra salt threshold value with biochar amendments. Journal of Plant Interactions, 13, 51–63.ElshaikhN. A.ZhipengL.DongliS.TimmL. C.2018Increasing the okra salt threshold value with biochar amendmentsJournal of Plant Interactions13516310.1080/17429145.2017.1418914Search in Google Scholar

Hoagland, D. R., and Arnon, D. I. (1950). The water-culture method for growing plants without soil. Circular. California Agricultural Experiment Station, 347, 32.HoaglandD. R.ArnonD. I.1950The water-culture method for growing plants without soilCircular. California Agricultural Experiment Station34732Search in Google Scholar

Hou, Z., Li, P., Gong, J., and Wang, Y.-N. (2007). Effect of different soil salinity levels and application rates of nitrogen on the growth of cotton under drip irrigation. Chinese Journal of Soil Science, 38, 681–686.HouZ.LiP.GongJ.WangY.-N.2007Effect of different soil salinity levels and application rates of nitrogen on the growth of cotton under drip irrigationChinese Journal of Soil Science38681686Search in Google Scholar

Huang, M., Zhang, Z., Zhai, Y., Lu, P., and Zhu, C. (2019). Effect of straw biochar on soil properties and wheat production under saline water irrigation. Agronomy, 9, 457.HuangM.ZhangZ.ZhaiY.LuP.ZhuC.2019Effect of straw biochar on soil properties and wheat production under saline water irrigationAgronomy945710.3390/agronomy9080457Search in Google Scholar

Javed, Q., Azeem, A., Sun, J., Ullah, I., Jabran, K., Anandkumar, A., Prabakaran, K., Buttar, N., and Du, D. (2019a). Impacts of salt stress on the physiology of plants and opportunity to rewater the stressed plants with diluted water: A review. Applied Ecology and Environmental Research, 17, 12583–12604.JavedQ.AzeemA.SunJ.UllahI.JabranK.AnandkumarA.PrabakaranK.ButtarN.DuD.2019aImpacts of salt stress on the physiology of plants and opportunity to rewater the stressed plants with diluted water: A reviewApplied Ecology and Environmental Research17125831260410.15666/aeer/1705_1258312604Search in Google Scholar

Javed, Q., Sun, J., Azeem, A., Ullah, I., Huang, P., Kama, R., Jabran, K., and Du, D. (2019b). The enhanced tolerance of invasive Alternanthera philoxeroides over native species under salt-stress in China. Applied Ecology and Environmental Research, 17, 14767–14785.JavedQ.SunJ.AzeemA.UllahI.HuangP.KamaR.JabranK.DuD.2019bThe enhanced tolerance of invasive Alternanthera philoxeroides over native species under salt-stress in ChinaApplied Ecology and Environmental Research17147671478510.15666/aeer/1706_1476714785Search in Google Scholar

Javed, Q., Wu, Y., Azeem, A., and Ullah, I. (2017). Evaluation of irrigation effects using diluted salted water based on electrophysiological properties of plants. Journal of Plant Interactions, 12, 219–227.JavedQ.WuY.AzeemA.UllahI.2017Evaluation of irrigation effects using diluted salted water based on electrophysiological properties of plantsJournal of Plant Interactions1221922710.1080/17429145.2017.1319501Search in Google Scholar

Javed, Q., Wu, Y., Xing, D., Ullah, I., Azeem, A., and Rasool, G. (2018). Salt-induced effects on growth and photosynthetic traits of Orychophragmus violaceus and its restoration through re-watering. Brazilian Journal of Botany, 41, 29–41.JavedQ.WuY.XingD.UllahI.AzeemA.RasoolG.2018Salt-induced effects on growth and photosynthetic traits of Orychophragmus violaceus and its restoration through re-wateringBrazilian Journal of Botany41294110.1007/s40415-017-0432-xSearch in Google Scholar

Jouyban, Z. (2012). The effects of salt stress on plant growth. Technical Journal of Engineering and Applied Sciences, 2, 7–10.JouybanZ.2012The effects of salt stress on plant growthTechnical Journal of Engineering and Applied Sciences2710Search in Google Scholar

Maas, E. V., and Hoffman, G. J. (1977). Crop salt tolerance–current assessment. Journal of the Irrigation and Drainage Division, American Society of Civil Engineers, 103, 115–134.MaasE. V.HoffmanG. J.1977Crop salt tolerance–current assessmentJournal of the Irrigation and Drainage Division, American Society of Civil Engineers10311513410.1061/JRCEA4.0001137Search in Google Scholar

Maqbool, N., Wahid, A., and Basra, S. (2016). Varied patterns of sprouting and nutrient status of sugarcane sprouts in simulated and natural saline/sodic soils across two growing seasons. International Journal of Agriculture and Biology, 18(4), 873–880.MaqboolN.WahidA.BasraS.2016Varied patterns of sprouting and nutrient status of sugarcane sprouts in simulated and natural saline/sodic soils across two growing seasonsInternational Journal of Agriculture and Biology18487388010.17957/IJAB/15.0209Search in Google Scholar

Munns, R., James, R. A., Xu, B., Athman, A., Conn, S. J., Jordans, C., Byrt, C. S., Hare, R. A., Tyerman, S. D., and Tester, M. (2012). Wheat grain yield on saline soils is improved by an ancestral Na+ transporter gene. Nature Biotechnology, 30, 360.MunnsR.JamesR. A.XuB.AthmanA.ConnS. J.JordansC.ByrtC. S.HareR. A.TyermanS. D.TesterM.2012Wheat grain yield on saline soils is improved by an ancestral Na+ transporter geneNature Biotechnology3036010.1038/nbt.212022407351Search in Google Scholar

Parida, A. K., and Das, A. B. (2004). Effects of NaCl stress on nitrogen and phosphorous metabolism in a true mangrove Bruguiera parviflora grown under hydroponic culture. Journal of Plant Physiology, 161, 921–928.ParidaA. K.DasA. B.2004Effects of NaCl stress on nitrogen and phosphorous metabolism in a true mangrove Bruguiera parviflora grown under hydroponic cultureJournal of Plant Physiology16192192810.1016/j.jplph.2003.11.00615384403Search in Google Scholar

Qados, A. M. A. (2011). Effect of salt stress on plant growth and metabolism of bean plant Vicia faba (L.). Journal of the Saudi Society of Agricultural Sciences, 10, 7–15.QadosA. M. A.2011Effect of salt stress on plant growth and metabolism of bean plant Vicia faba (L.)Journal of the Saudi Society of Agricultural Sciences1071510.1016/j.jssas.2010.06.002Search in Google Scholar

Qiu, R., Jing, Y., Liu, C., Yang, Z., and Wang, Z. (2017). Response of hot pepper yield, fruit quality, and fruit ion content to irrigation water salinity and leaching fractions. HortScience, 52, 979–985.QiuR.JingY.LiuC.YangZ.WangZ.2017Response of hot pepper yield, fruit quality, and fruit ion content to irrigation water salinity and leaching fractionsHortScience5297998510.21273/HORTSCI12054-17Search in Google Scholar

Riccardi, M., Pulvento, C., Lavini, A., D’andria, R., and Jacobsen, S. E. (2014). Growth and ionic content of quinoa under saline irrigation. Journal of Agronomy and Crop Science, 200, 246–260.RiccardiM.PulventoC.LaviniA.D’andriaR.JacobsenS. E.2014Growth and ionic content of quinoa under saline irrigationJournal of Agronomy and Crop Science20024626010.1111/jac.12061Search in Google Scholar

Saleem, A., Ashraf, M., and Akram, N. (2011). Salt (NaCl)-induced modulation in some key physio-biochemical attributes in okra (Abelmoschus esculentus L.). Journal of Agronomy and Crop Science, 197, 202–213.SaleemA.AshrafM.AkramN.2011Salt (NaCl)-induced modulation in some key physio-biochemical attributes in okra (Abelmoschus esculentus L.)Journal of Agronomy and Crop Science19720221310.1111/j.1439-037X.2010.00453.xSearch in Google Scholar

Senguttuvel, P., Vijayalakshmi, C., Thiyagarajan, K., Kannanbapu, J., Kota, S., Padmavathi, G., Geetha, S., Sritharan, N., and Viraktamath, B. (2014). Changes in photosynthesis, chlorophyll fluorescence, gas exchange parameters and osmotic potential to salt stress during early seedling stage in rice (Oryza sativa L.). SABRAO Journal of Breeding and Genetics, 46(1), 120–135.SenguttuvelP.VijayalakshmiC.ThiyagarajanK.KannanbapuJ.KotaS.PadmavathiG.GeethaS.SritharanN.ViraktamathB.2014Changes in photosynthesis, chlorophyll fluorescence, gas exchange parameters and osmotic potential to salt stress during early seedling stage in rice (Oryza sativa L.)SABRAO Journal of Breeding and Genetics461120135Search in Google Scholar

Shahid, M. A., Pervez, M. A., Balal, R. M., Ahmad, R., Ayyub, C. M., Abbas, T., and Akhtar, N. (2011). Salt stress effects on some morphological and physiological characteristics of okra (Abelmoschus esculentus L.). Soil and Environment, 30(1), 66–73.ShahidM. A.PervezM. A.BalalR. M.AhmadR.AyyubC. M.AbbasT.AkhtarN.2011Salt stress effects on some morphological and physiological characteristics of okra (Abelmoschus esculentus L.)Soil and Environment3016673Search in Google Scholar

She, D., Sun, X., Gamareldawla, A. H., Nazar, E. A., Hu, W., and Edith, K. (2018). Benefits of soil biochar amendments to tomato growth under saline water irrigation. Scientific Reports, 8, 1–10.SheD.SunX.GamareldawlaA. H.NazarE. A.HuW.EdithK.2018Benefits of soil biochar amendments to tomato growth under saline water irrigationScientific Reports811010.1038/s41598-018-33040-7617047230283026Search in Google Scholar

Taïbi, K., Taïbi, F., Abderrahim, L. A., Ennajah, A., Belkhodja, M., and Mulet, J. M. (2016). Effect of salt stress on growth, chlorophyll content, lipid peroxidation and antioxidant defence systems in Phaseolus vulgaris L. South African Journal of Botany, 105, 306–312.TaïbiK.TaïbiF.AbderrahimL. A.EnnajahA.BelkhodjaM.MuletJ. M.2016Effect of salt stress on growth, chlorophyll content, lipid peroxidation and antioxidant defence systems in Phaseolus vulgaris L.South African Journal of Botany10530631210.1016/j.sajb.2016.03.011Search in Google Scholar

Tavakkoli, E., Fatehi, F., Coventry, S., Rengasamy, P., and Mcdonald, G. K. (2011). Additive effects of Na+ and Cl ions on barley growth under salinity stress. Journal of Experimental Botany, 62, 2189–2203.TavakkoliE.FatehiF.CoventryS.RengasamyP.McdonaldG. K.2011Additive effects of Na+ and Cl ions on barley growth under salinity stressJournal of Experimental Botany622189220310.1093/jxb/erq422306069821273334Search in Google Scholar

Wang, W., Yan, X., Jiang, Y., Qu, B., and Xu, Y. (2012). Effects of salt stress on water content and photosynthetic characteristics in Iris lactea var. chinensis seedlings. Middle-East Journal of Scientific Research, 12, 70–74.WangW.YanX.JiangY.QuB.XuY.2012Effects of salt stress on water content and photosynthetic characteristics in Iris lactea var. chinensis seedlingsMiddle-East Journal of Scientific Research127074Search in Google Scholar

Xing, D., Xu, X., Wu, Y., Liu, Y., Wu, Y., Ni, J., and Azeem, A. (2018). Leaf tensity: A method for rapid determination of water requirement information in Brassica napus L. Journal of Plant Interactions, 13, 380–387.XingD.XuX.WuY.LiuY.WuY.NiJ.AzeemA.2018Leaf tensity: A method for rapid determination of water requirement information in Brassica napus L.Journal of Plant Interactions1338038710.1080/17429145.2018.1478006Search in Google Scholar

Zamani, G. R., Shaabani, J., and Izanloo, A. (2017). Silicon effects on the growth and yield of chickpea under salinity stress. International Journal of Agriculture and Biology, 19, 1475–1482.ZamaniG. R.ShaabaniJ.IzanlooA.2017Silicon effects on the growth and yield of chickpea under salinity stressInternational Journal of Agriculture and Biology1914751482Search in Google Scholar

Zhang, M., Wu, Y., Xing, D., Zhao, K., and Yu, R. (2015). Rapid measurement of drought resistance in plants based on electrophysiological properties. Transactions of the ASABE, 58, 1441–1446.ZhangM.WuY.XingD.ZhaoK.YuR.2015Rapid measurement of drought resistance in plants based on electrophysiological propertiesTransactions of the ASABE581441144610.13031/trans.58.11022Search in Google Scholar

Empfohlene Artikel von Trend MD

Planen Sie Ihre Fernkonferenz mit Scienceendo