Next Article in Journal
Identification and Characterization of the Glutathione Peroxidase (GPX) Gene Family in Watermelon and Its Expression under Various Abiotic Stresses
Previous Article in Journal
Management of Nitrapyrin and Pronitridine Nitrification Inhibitors with Urea Ammonium Nitrate for Winter Wheat Production
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agronomy
Volume 8
Issue 10
10.3390/agronomy8100205
agronomy-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Screening and Evaluation of Saline–Alkaline Tolerant Germplasm of Rice (Oryza sativa L.) in Soda Saline–Alkali Soil

by
Hao Wang
1,
Tetsuo Takano
2 and
Shenkui Liu
3,*
1
Alkali Soil Natural Environmental Science Center (ASNESC), Northeast Forestry University, Harbin 150040, China
2
Asian Natural Environmental Science Center, The University of Tokyo, Nishitokyo-shi, Tokyo 188-0002, Japan
3
State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University, Lin’an, Hangzhou 311300, China
*
Author to whom correspondence should be addressed.
Agronomy 2018, 8(10), 205; https://doi.org/10.3390/agronomy8100205
Submission received: 17 August 2018 / Revised: 16 September 2018 / Accepted: 21 September 2018 / Published: 25 September 2018
Browse Figures
Versions Notes

Abstract

:
The improvement and development of saline–alkali land is of great significance for promoting food production and sustainable development. It is necessary to study the mechanism of saline–alkaline tolerance and breed saline–alkaline tolerant crops to improve the utilization of saline–alkali land. For this study, we conducted a three-year pot experiment to screen the saline–alkaline tolerant germplasm of 72 rice genotypes from hundreds of elite cultivars during the whole growth period using a certain proportion of soda saline–alkali soil. The selected salt-tolerant variety was combined with a salt-sensitive variety to analyze the saline–alkaline tolerance mechanism by using the saline–alkaline soil leachate. We eliminated 36 genotypes with low seedling survival rates under salt–alkali stress, and the salt-tolerant Jiudao-66 (D68) variety had a higher survival rate than most varieties. The membership degree of Jiudao-66, according to the salt tolerance index of multiple agronomic traits, is higher than that of 34 varieties, with a higher survival rate except when compared to D36. The survival rate and these salt tolerance indexes of Jiudao-66 were significantly higher than those of Kitaake (salt-sensitive). Under the stress of leachate, the content of proline and soluble sugars in the shoots of Jiudao-66 were higher than that of Kitaake, and the total antioxidant capacity was stronger than that of Kitaake. However, the content of malondialdehyde was lower than that of Kitaake. Additionally, the Na+/K+ ratios in shoots and roots were not significantly differently between Kitaake and Jiudao-66. The results showed that Jiudao-66, as a salt-tolerant variety, is more tolerant to salt and alkali in a near-natural state due to its stronger tolerance of osmotic stress, and it can accumulate more proline and soluble sugars under stress. At the same time, Jiudao-66 also has a stronger antioxidant capacity. Its ion regulation ability has no obvious advantage.

1. Introduction

Arable land supports grain production and is a fundamental guarantee of national food security. Soil saline–alkalization is a major abiotic stressor on the world’s agriculture, causing considerable damage to crop growth and resulting in serious losses in crop production [1,2,3,4]. The salinization area of land has exceeded 800 million hectares worldwide [5]. The saline–alkali land area of China is about 100 million hectares, mainly distributed in northeast, northwest, and north China, as well as coastal areas [6]. The area of saline–alkali land in the Songnen Plain in northeast China has reached 3.73 million hectares [7]. Saline–alkaline soil can be mainly classified into two types: saline soil and alkaline soil. The main components (neutral salt containing NaCl + Na2SO4 versus alkaline salt containing NaHCO3 + NaCO3), EC (electrical conductivity) value, pH value, and other properties of these two soil types are greatly different [8]. The effects of saline soil and alkaline soil on plants are not identical. Both of them will produce ionic and osmotic stress, but alkaline soil will also form a high pH environment. High pH will affect plants and soil, so alkaline stress is more harmful to plants than salt stress [9,10]. The saline–alkali land in the Songnen Plain is made up of soda saline–alkali soil. It is one of the three typical soda saline–alkali soil distribution areas in the world [7]. Taking a large amount of saline–alkali land as a reserve arable land resource and realizing the “transformation into arable land” of the saline–alkali land by virtue of restoration and improvement is of great significance for sustainable development.
The salt and alkali tolerance mechanisms of plants mainly include ion homeostasis, osmoregulation, and antioxidant activity. Ion toxicity is the primary cause of salt damage. Osmotic stress and oxidative damage are secondary causes of salt damage. Under salt–alkali stress conditions, plants will absorb a large amount of Na+ and inhibit the absorption of other nutrients, such as K+, resulting in ion imbalance and toxicity. The response mechanism of plants to ion toxicity is Na+ exclusion and compartmentation. Plants maintain low Na+/K+ through the regulation of a series of genes. Under salt–alkali stress conditions, the external water potential is too low, which will cause osmotic stress to dehydrate the plant cells. At this time, plants can accumulate compatible solutes in the cytoplasm, reduce their water potential, and ensure that the volume and turgor pressure of the cells is in a suitable range to alleviate water loss. In addition, this also keeps the stomata open and the CO2 concentration in the leaves at a high level, which can reduce the inhibition of plant photosynthesis [11]. Substances involved in plant osmoregulation include inorganic ions (such as Na+, K+, Cl−, Ca2+, etc.) and metabolites (such as sugars, organic acids, sugar alcohols, amino acids and their derivatives, etc.) [12]. Under normal conditions, the formation and elimination of reactive oxygen species (ROS) in plants is in a state of dynamic equilibrium. Saline–alkaline stress destroys this state, causing a large amount of ROS to accumulate in the plant, damaging the biomembrane system and causing a series of injuries until wilting occurs [13]. Under stress conditions, the plants scavenge excess reactive oxygen species with the help of antioxidant enzymes and antioxidants, protecting the integrity of the biomembrane structure and normal physiological functions from oxidative damage and improving the salt–alkali tolerance of the plants.
Rice (Oryza sativa L.) is one of the most important food crops. Half of the world’s population uses rice as a staple food, and about 60% of Chinese people use rice as a staple food [14]. Previous studies on saline–alkaline tolerance in rice have been carried out for a specific period, such as the seed germination stage, seedling stage, and reproductive stage. The treatment method was to simulate saline–alkali stress in a saline–alkali solution. They treated the seeds and the hydroponic plants with a saline–alkali solution [15,16,17,18,19,20] or watered the plants in the soil with a saline–alkali solution [21,22,23].
In this study, we applied a certain proportion of saline–alkaline soil and normal soil mixture to implement a detailed screening in the field of saline–alkaline-tolerant germplasm of rice during the whole plant growth period. We selected 72 genotypes from hundreds of elite varieties. After screening, 36 varieties were eliminated. Finally, we obtained a salt-tolerant variety from the remaining 36 varieties. Then, we applied the saline–alkaline soil leachate to analyze the physiological mechanism of the salt-tolerant rice variety. Field screening was combined with physiological mechanism analysis to find the salt–alkali tolerance mechanism of rice in the near-natural state. This salt-tolerant variety is suitable for QTL (quantitative trait locus) mapping. Our findings will lay a foundation for identifying new salt-tolerant QTLs and cultivate new salt-tolerant rice varieties.

2. Materials and Methods

2.1. Screening of Saline–Alkaline-Tolerant Germplasm of Rice

2.1.1. Study Site

The study was conducted at the field experimental station of the Alkali Soil Natural Environmental Science Center (ASNESC), Northeast Forestry University, Anda, Heilongjiang Province (46°27′ N, 125°22′ E) [24] in northeast China. Anda has a temperate continental semi-arid monsoon climate. The average annual temperature is 3.3 °C, along with a frost-free period of 137 days and 2746 °C of accumulated temperature beyond 10 °C [25]. The average annual precipitation, evaporation, and sunshine hours are 438 mm, 1300 mm, and 2660 h, respectively [7,25]. Anda City is one of the most severe salinization areas, with an area of 147,600 hectares of saline–alkaline land [26]. The soil type in the area is typical soda saline–alkaline soil. The salt in the soil contains a lot of soda. The pot experiment was conducted from April to October in 2011, 2012, and 2013.

2.1.2. Rice Cultivation, Experimentation, and Data Collection

Fully developed rice seeds were sown on disks filled with nursery substrate (peat and vermiculite in a 1:1 proportion) in a greenhouse at the end of April. Three (thirty seedlings in 2011) uniform, approximately 30-day-old seedlings were transplanted into a plastic pot (30 cm diameter × 25 cm depth). Every pot was filled with a potting mixture of normal soil and saline–alkaline soil (NS:SAS volume ratios of 0, 2:1, and 1:1; Table 1) in triplicate. Fifteen days after transplantation, a complex fertilizer (N-P2O5-K2O, 15-15-15, total nutrients ≥ 45%) was applied as topdressing for tillering. Then, the same topdressing was applied at the heading stage. The saline–alkaline soil was chosen and collected at 0–30 cm depth of wild “barren” lands in the serious salinization and alkalinization regions. All the pots were placed under the rain shelter of a PC (polycarbonate) sun sheet.

2.1.3. Germplasm Survey

Seventy-two rice varieties were screened and selected half candidates of saline–alkaline tolerance, in accordance with survival rates of rice seedlings from the pot experiment in 2011 (NS:SAS = 1:0 and 2:1, in triplicate). At the mature stage in 2012 and 2013, we determined the following parameters: plant height (PHT), the number of tillers per plant (TN), effective panicle number per plant (EPN), 1000-grain weight (TGW), spikelets of the main panicle (SMP), and number of filled spikelets (NFS). For further screening, a potting mixture (1:1) was added in 2013 to the genotypes from 2011 and 2012. A typical experimental material, Nipponbare, and a salt-sensitive rice variety, Kitaake, were also tested.

2.2. Physiological Mechanism Analysis of Saline–Alkaline Tolerant Genotypes of Rice

2.2.1. Plant Material, Growth Conditions, and Stress Treatments

Two Japonica rice genotypes with different levels of saline–alkaline tolerance were used in this study: “Jiudao-66” (tolerant to SA, i.e., “D68”) and “Kitaake” (sensitive to SA). Seeds were disinfected with 3% NaClO for 30 min and rinsed with tap water six times. One day after soaking, the seeds were transferred into moist filter paper in a Petri dish and germinated for 4 days at 30 °C under bright light. The germinated seeds were then transplanted onto two multi-well plates embedded in PVC (Polyvinyl chloride) foam board floating on a plastic box containing 4 L of water for 10 days. All boxes were put in a cultivation room under the following conditions: 26–28 °C, 12 h photoperiod, 10,000 lx illuminance, and a relative humidity of approximately 70%. Then, the water was replaced with a nutrient solution containing: 1.44 mM NH4NO3, 0.32 mM NaH2PO4, 0.6 mM K2SO4, 1.0 mM CaCl2, 1.6 mM MgSO4, 0.072 mM Fe-EDTA (Ethylene Diamine Tetraacetic Acid), 0.2 mM Na2SiO3, 9.1 μM MnCl2, 0.154 μM ZnSO4, 0.156 μM CuSO4, 18.5 μM H3BO3, and 0.526 μM H2MoO4 at pH 5.5 [27]. The Jiudao-66 and Kitaake seedlings were grown in this culture solution for 15 days. The water and solution were refreshed every three days.
To analyze tolerance to saline–alkaline stress, six boxes were divided into two groups as the control and saline–alkaline treatment in triplicate. Three of the boxes were kept planted in the culture solution as control. The other three boxes were replaced with 4 L saline–alkaline soil leachate for stress treatment. The leachate was extracted from 2 L saline–alkaline soil mixed with 4 L of water (stock solution). Four liters of tap water were poured into 2 L of saline–alkaline soil, stirred well, and filtered with filter paper to remove impurities. The saline–alkaline soil used for extraction was chosen and collected at 0–10 cm depth of wild “barren” lands, so it has a higher salinity. The air-dried soil was sieved using a 5 × 5 cm screen and mixed adequately. In our experiment, we used a quarter of the stock solution for stress treatment (tap water:stock solution = 3:1, volume). The process of obtaining leachate and its essential characteristics are shown Supplementary Figure S1 and Table S1. We collected samples after 24 h of control and stress treatments for various measurements.

2.2.2. Measurement of Chlorophyll Content

Leaves (0.1 g) were sampled, cut into pieces, and extracted with aqueous ethanol (95% v/v) in both Kitaake and Jiudao-66 plants to determine chlorophyll content. The absorbance (A) of the supernatant was determined at wavelengths of 645 and 663 nm. Total chlorophyll content was calculated using the following formula: 8.02 A663 + 20.21 A645. It was expressed using the unit mg of chlorophyll g−1 fresh weight.

2.2.3. Determination of Na+ and K+ Concentration

Shoots and roots of rice seedlings were oven-dried at 70 °C (deactivation of enzymes occurred at 105 °C during the initial stage) until they reached a constant mass and a 0.2 g dry sample was weighed separately. They were crushed and digested with 5 mL nitric acid and 2 mL perhydrol using a microwave system. Ion content was determined by inductively coupled plasma mass spectrometry (ICAP6300; Thermo Scientific, Waltham, MA, USA).

2.2.4. Determination of Proline and Soluble Sugars Content

Leaves and roots (0.1 g) were sampled for determination, and the roots were rinsed clean before weighing. Proline and soluble sugar content were determined by using commercial kits (Jiancheng Bioengineering Institute, Nanjing, Jiangsu, China) according to the manufacturer’s instructions.

2.2.5. Measurements of Total Antioxidant Capacity (T-AOC) and Malondialdehyde (MDA) Content

Leaves and roots (0.1 g) were sampled for measurement and the roots were rinsed clean before weighing. T-AOC and MDA content were also measured using commercial kits (Jiancheng Bioengineering Institute, Nanjing, Jiangsu, China) according to the manufacturer’s instructions. We defined one T-AOC unit (U) as the value where 1 g of fresh plant material extract with 1 mL normal saline solution increases the absorbance (OD) value of the reaction system by 0.01 in one minute at 37 °C.

2.3. Statistical Analysis

The survival rates of seedlings from three of the same pots in 2011 were measured and averaged (means ± SD, n = 3). The parameters of growth and yield components from a pot of all plants were averaged as one repetition according to the final number of survivors in 2012 and 2013. The relative parameters (salt tolerance index or STI) were the ratios of the values under stress treatments (i.e., 2:1 and 1:1 potting mixtures) to the corresponding values of controls (i.e., 1:0 potting mixture). STI = XST/XC. We screened the remaining 36 varieties from 2011 using the membership degree (MD) of the relative parameters in 2012. The MD of a variety represents the mean value of the membership values (MV) of each single (relative) parameter such as PHT, TN, EPN, and etc. The formula MV = (X − Xmin)/(Xmax − Xmin) [28] was used to calculate the MV for a specific parameter (such as PHT) of a variety, in which X was a single parameter of the variety under stress treatment (2:1 mixture). Xmax and Xmin were the maximum and minimum values of X in 36 rice varieties, respectively. The salt tolerance indexes were analyzed by the analysis of variance using the SPSS 17.0 (Statistical Product and Service Solutions, SPSS Statistics for Windows, Version 17.0. SPSS Inc., Chicago, IL, USA) statistical software in 2013. A general linear model (GLM) and Duncan’s multiple range test (DMRT) were used for significance comparison (p < 0.05, p < 0.01). The physiological data were also analyzed through the analysis of variance using the SPSS statistical software. Significant differences were evaluated using Student’s t-test (p < 0.05). All data represents an average of three repeat measurements and the standard deviation.

3. Results

3.1. Screening of Saline–Alkaline Tolerant Germplasm of Rice

3.1.1. Initial Screening in 2011

The seedling survival rates in the 2:1 potting mixture (NS:SAS = 2:1) are shown in Table 2. We investigated the effect of saline–alkaline soil on the survival rate of rice seedlings at 30 days after transplanting. The survival rates of seedlings under saline–alkaline stress decreased to 45.6–97.8% while they were 97.8% (two varieties), 98.9% (nine varieties), and 100% (61 varieties) in normal soil (NS:SAS = 1:0). According to these results, we selected 36 varieties for further screening in 2012.

3.1.2. Screening by Whole Growth Period in 2012

To characterize 36 varieties in the whole growth period under saline–alkaline stress, six parameters of the growth and yield components were surveyed after harvest. Then the relative parameters (salt tolerance index) of PHT, TN, EPN, TGW, SMP, and NFS were calculated (NS:SAS = 2:1). The MD values of 36 varieties according to their salt tolerance index are shown in Table 3. D36 (MD = 0.90) and D68 (MD = 0.88) were two varieties with the best overall performance under saline–alkaline stress. These two varieties could be further used as salt-tolerant varieties.

3.1.3. Further Verification in 2013

We compared two rice varieties (a salt-sensitive variety called “Kitaake” and a well-known variety called “Nipponbare”) with the previously studied D36 and D68 varieties. Then, we examined the growth performance and final yield composition of the four rice varieties during their growth period. In order to verify the previous results, we also added a 1:1 potting mixture as the experimental treatment. As shown in Figure 1A, no differences in the growth of four genotypes were detected when grown in a 1:0 potting mixture (NS:SAS = 1:0). Kitaake and Nipponbare were severely stressed in the 2:1 potting mixture, which caused only some seedlings to survive. Meanwhile, D36 and D68 were slightly stressed in this potting mixture, and the seedlings all survived. Kitaake and Nipponbare were more severely stressed in the 1:1 potting mixture. The seedlings were hardly able to grow. D36 and D68 were severely stressed in this potting mixture, but some of the seedlings grew well.
The salt tolerance indexes of PHT, TN, EPN, TGW, SMP, and NFS with Kitaake and Nipponbare in the 2:1 potting mixture were significantly lower than that of D36 and D68. All seedlings of Kitaake and Nipponbare in the 1:1 potting mixture were eventually dead with no gains. The salt tolerance indexes of PHT, TN, EPN, TGW, SMP, and NFS with D36 and D68 in the 1:1 potting mixture were lower than those in the 2:1 potting mixture, but harvest could be obtained. The above results indicated that the stress effect was obvious, and the salt and alkali tolerance of D36 and D68 was significantly stronger than that of Kitaake and Nipponbare.
Among the four varieties, Nipponbare was not harvested (all the plants failed to mature) due to the photoperiod, i.e., the sunshine hours in Heilongjiang Province is of the long-day characteristic with 15 h, while Nipponbare has a shorter photoperiod. Most salt tolerance indexes of D36 were higher than those of D68 (the differences were not significant), but its maturity was late. The saline–alkaline stress also delayed the maturity period (Table S2). Therefore, D36 was not harvested in the 1:1 potting mixture. D36 also had poorer rice quality than D68 (Figure S2).
Consequently, D68 and Kitaake were selected as experimental materials for the next experiment. The name of D68 was “Jiudao-66”.

3.2. Evaluation of Salt and Alkali Tolerance and Physiological Mechanism Analysis of Jiudao-66

3.2.1. Effects of Saline–Alkaline Stress on Seedlings

To contrast the salt-tolerant rice variety Jiudao-66 and salt-sensitive rice variety Kitaake (pre-validation), 25-day-old rice seedlings of the two varieties were exposed to a quarter of saline–alkaline soil leachate (1/4 stock solution) for 24 h. After 24 h, the seedlings exposed to leachate were transferred to the previous culture solution for recovery. Then, we monitored the effects of saline–alkaline stress on the seedlings of the two genotypes. No differences between the two genotypes were observed when grown in the control solution. Saline–alkaline treatment for 24 h caused the seedlings to wilt. However, Jiudao-66 was better in this regard than Kitaake (Figure 2A). We measured the foliar chlorophyll content of plants undergoing control and saline–alkaline treatment. Exposure to leachate led to a reduction in foliar chlorophyll content in both Kitaake and Jiudao-66 seedlings, but the chlorophyll content in Jiudao-66 was significantly higher than that of Kitaake under stress, while there were no differences in the chlorophyll content in the two genotypes under control conditions (Figure 2B).

3.2.2. Effect of Saline–Alkaline Stress on Na+ and K+ Concentrations

In the stress treatments, the Na+ concentrations in the roots and shoots of Kitaake and Jiudao-66 seedlings were significantly higher than in the control treatments, while K+ concentrations decreased compared to controls (Figure 3A,B,D,E). The K+ concentrations in the roots of the two varieties decreased markedly, while it decreased less in shoots. In the shoots, Kitaake plants showed lower K+ and higher Na+ concentrations than the Jiudao-66 plants under the control treatments. The Na+/K+ ratios of Kitaake were significantly higher than those of Jiudao-66. The K+ concentrations, Na+ concentrations, and Na+/K+ ratios in shoots of Kitaake under saline–alkaline stress were not significantly different from those of Jiudao-66 (Figure 3A–C). In the roots, Kitaake plants also showed lower K+ and higher Na+ concentrations than Jiudao-66 plants under the control treatment. The Na+/K+ ratios of Kitaake were also significantly higher than those of Jiudao-66 (Figure 3D–F). The Na+ concentrations in the roots of Kitaake under the saline–alkaline stress treatment were significantly lower than those of Jiudao-66 (Figure 3E). The K+ concentrations and Na+/K+ ratios in the roots of Kitaake under saline–alkaline stress were not significantly different from those of Jiudao-66 (Figure 3D,F). In general, the Na+/K+ ratios in the shoots and roots of Kitaake and Jiudao-66 plants were not significantly different under saline–alkaline stress.

3.2.3. Effect of Saline–Alkaline Stress on Osmoregulation

The proline content in shoots of Jiudao-66 was higher than that in Kitaake under the control treatment. There were significant increases in shoot proline content of both Kitaake and Jiudao-66 seedlings under saline–alkaline stress. However, the increase in shoot proline content of Jiudao-66 plants was significantly higher than that in Kitaake plants under stress. The proline content in the roots of Jiudao-66 and Kitaake plants under control conditions were comparable. There was not much increase in the root proline content of Kitaake and Jiudao-66 seedlings under saline–alkaline stress. In addition, the root proline content between Jiudao-66 and Kitaake plants was not significant under stress (Figure 4A,B).
The two genotypes had a comparable soluble sugar content in their shoots and roots under the control conditions. The soluble sugar content was markedly increased in the shoots and roots of both Kitaake and Jiudao-66 seedlings under stress conditions. The increase in the shoot soluble sugar content of Jiudao-66 plants was greater than that in Kitaake plants under stress. However, no obvious differences in root soluble sugar content was found in Jiudao-66 and Kitaake plants under stress (Figure 4C,D).

3.2.4. Effect of Saline–Alkaline Stress on Oxidative Stress

Under abiotic stress, plants often exhibit symptoms of oxidative stress. The T-AOC and MDA content reflect the ability of the organism to cope with oxidative stress and the extent of damage under stress conditions. There were increases in shoot and root T-AOCs of both Kitaake and Jiudao-66 seedlings under saline–alkaline stress. The shoot and root T-AOCs of Jiudao-66 were significantly higher than those of Kitaake under control and saline–alkaline stress conditions (Figure 5A,B). There were increases in shoot and root MDA content of both Kitaake and Jiudao-66 seedlings under saline–alkaline stress. The shoot and root MDA content of Jiudao-66 was significantly lower than those of Kitaake under stress, while they had no significant differences under control conditions (Figure 5C,D).

4. Discussion

The soda saline–alkali soil on the Songnen Plain has a high pH value, high EC value, and high content of carbonate (bicarbonate) (Table 1). The soil texture is very fine, the structure is poor, and the permeability is very low. Agricultural production on saline–alkali land in this area is a serious obstacle to growing. Plants are often subjected to more severe stress than in other types of saline–alkali soil.
In the past, studies on salt and alkali tolerance were often carried out by means of a salt solution (e.g., neutral salt or alkaline salt) to simulate stress conditions during screening and evaluation. Researchers grew rice in a hydroponic culture solution with or without salt stress [27,29,30,31,32,33]. Previous reports have also completed phenotypic evaluation using irrigated brine or incubated rice in salt solution with perforated pots [34,35,36,37]. Takagi et al. screened 6000 ethyl methanesulfonate (EMS) mutant lines of a local elite cultivar. Young seedlings were subjected to salinity treatment in 50% GEX (Gex Co., Ltd., Osaka, Japan) artificial seawater containing 1.5% NaCl. They used a MutMap (next generation sequencing) method to accelerate breeding of a salt-tolerant rice cultivar [38]. Others findings reported implement screening and evolution during the germination period [39,40,41]. Importantly, Negrão et al. suggested that the salt and alkali tolerance of rice varied during different growth stages [42]. We used potting mixture with saline–alkali soil to screen the saline–alkaline tolerant germplasm of rice during the whole growth period. Seventy-two genotypes were screened with three kinds of treatment, including a control treatment. The results showed that there were differences in survival rate, related traits of growth, and yield among these rice varieties. Finally, we selected a salt-tolerant rice variety (Jiudao-66, i.e., D68) and a salt-sensitive rice variety (Kitaake) as a combination for consecutive experiments. During the screening experiments, we found that rice plants could survive after transplantation, and they would grow until harvest. Thus, the seedling stage is a key period for the resistance test. In agricultural production, the varieties with a strong salt and alkali tolerance at the seedling stage were selected to grow in normal soil first. Then, the appropriately aged seedlings were transplanted into saline–alkali soil with light salinity, so as to succeed in planting rice on saline–alkali land and developing backup farmland. After screening, we used the saline–alkaline soil leachate to evaluate salt and alkali tolerance and analyze the physiological mechanisms of the salt-tolerant rice variety. This has not been reported yet. The leachate contains plenty of tiny black soil colloid, so it looks black while the saline–alkaline soil is white or normal in color (Figure S1). The tiny colloid may also hinder the absorption of water and mineral elements by the roots. It can better represent saline–alkali land, and its properties are like those of saline–alkaline soil. The experimental results have a more important significance for crop production.
Rice plants generally tolerate salt through three main mechanisms: ion exclusion, osmotic tolerance, and tissue tolerance [43]. We determined the K+ content, Na+ content, proline content, soluble sugars content, T-AOC, and MDA content in shoots and roots of the plants under control and stress conditions. Ion exclusion mainly prevents excessive Na+ from accumulating in the leaves during sodium transport processes [44]. Plants with a strong tolerance to saline stress often have a high K+ and low Na+ concentration in their shoots. The Na+/K+ ratio is often considered as an indicator of plant tolerance to saline stress [45]. However, some studies have confirmed that the Na+/K+ ratio of the shoots is not related to the salt and alkali tolerance of the plants [46,47,48,49,50,51]. Li et al. considered that salt-tolerant rice plants can sequester Na+ in a vacuole, thus minimizing its toxic effect under salt stress. In the present study, a comparable Na+/K+ ratio was observed in Kitaake and Jiudao-66 under stress, suggesting that other mechanisms may be responsible for salt and alkali tolerance. However, we found that Kitaake plants had a higher Na+/K+ ratio in shoots and roots than Jiudao-66 plants under control conditions. This showed that Jiudao-66 has a stronger growth vigor, which can avoid the toxic effects of salinity [43]. Most plants accumulate some organic solutes to cope with osmotic stress. The accumulation of compatible solutes is generally considered to be a basic strategy to avoid plant salt damage. Compatible solutes accumulate as osmoprotectants in the cytosol, helping to reduce the cytoplasmic water potential [50]. Various sugars (e.g., fructose, glucose, and sucrose), polysaccharides (e.g., trehalose, raffinose, and fructans), sugar alcohols (e.g., mannitol and glycerol), amino acids, and derivatives (e.g., proline, glycine-betaine, and proline-betaine) all have this function [12,51]. In the present study, we found that Jiudao-66 plants accumulated more proline and soluble sugars in shoots than Kitaake under stress, while they have comparable amounts of proline and soluble sugars in roots under stress. The greater amount of osmoprotectants of Jiudao-66 in the shoots caused it to have more effective osmoregulation in osmotic stress and a stronger salt and alkali tolerance than Kitaake. As byproducts of photosynthesis, respiration, and photorespiration, more and more harmful reactive oxygen species (ROS) are produced under salinity stress. Excessive production of cytotoxic ROS causes oxidative damage to different cellular components, including membrane lipids, proteins, and nucleic acids [42]. To avoid excessive accumulation of ROS, ROS scavenging mechanisms, including enzymatic and non-enzymatic (antioxidants) mechanisms, are often activated in plants [32]. T-AOC reflects the total capacity to scavenge ROS, including various related enzymes (e.g., superoxide dismutases, peroxidases, etc.) and antioxidants (e.g., ascorbic acid, carotene, etc.). The level of MDA indirectly reflects the severity of oxidative damage. In the present study, Jiudao-66 had a stronger total antioxidant capacity and lower MDA content than Kitaake, under stress. Jiudao-66 could scavenge more ROS under stress conditions, which helped to improve its salt and alkali tolerance. Furthermore, Jiudao-66 had a stronger total antioxidant capacity than Kitaake under control conditions, probably due to its high antioxidant content.
In addition, some recent studies use RNA-seq and genome-wide analysis to describe the relationship of miRNAs (target mRNAs), differentially expressed genes (DEGs), transgenic overexpression, etc. with salt tolerance, abiotic stresses in rice, and other crops. Manu Kumar et al. elaborated on the relationship of OsSta2 with salt tolerance and abiotic stress in rice [52,53,54,55,56,57,58]. Salt tolerant varieties can be produced using marker-assisted selection or genetic engineering by introducing salt-tolerance genes [43]. Utilizing next generation sequencing and molecular markers, an F6:7 RIL (Recombinant Inbred Lines) population (about 130) derived from a cross of Kitaake with Jiudao-66 was used to identify quantitative trait loci for salt and alkali tolerance in rice.

5. Conclusions

In conclusion, we obtained a salt-tolerant rice variety (Jiudao-66) through screening in the field. Then, we combined this with a salt-sensitive variety (Kitaake) to analyze the salt and alkali tolerance mechanism of the rice. Jiudao-66 is more tolerant to salt and alkali because of its stronger ability to synthesize and accumulate proline and soluble sugars and its stronger antioxidant capacity. Our findings indicate that Jiudao-66 has a greater tolerance against osmotic stress and a more effective ROS detoxifying system than Kitaake under salt–alkali stress. Our findings will lay a foundation for mapping saline–alkaline tolerant QTLs.

Supplementary Materials

The following are available online at https://www.mdpi.com/2073-4395/8/10/205/s1, Figure S1: The obtainment of leachate, Figure S2: The rice quality of D36 and D68, Table S1: The leachate’s essential characteristics, Table S2: The maturity of D36 and D68 in the potting mixture.

Author Contributions

H.W. and S.L. conceived and designed the experiments. H.W. performed the experiments. H.W. analyzed the data. S.L. and T.T. contributed reagents, materials, and analysis tools. H.W. wrote the manuscript. S.L. and T.T. revised and approved the final article.

Funding

This work was supported by the Program for Changjiang Scholars, Innovative Research Team in University (PCSIRT) (IRT_17R99) and the Special Fund for Forest Scientific Research in Public Welfare (201404220).

Acknowledgments

We thank the reviewers and editors for their exceptionally helpful comments about the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Pascale, S.D.; Maggio, A.; Barbieri, G. Soil salinization affects growth, yield and mineral composition of cauliflower and broccoli. Eur. J. Agron. 2005, 23, 254–264. [Google Scholar] [CrossRef]
  2. Qadir, M.; Noble, A.D.; Schubert, S.; Thomas, R.J.; Arslan, A. Sodicity-induced land degradation and its sustainable management: Problems and prospects. Land Degrad. Dev. 2006, 17, 661–676. [Google Scholar] [CrossRef]
  3. Zhang, J.; Mu, C. Effects of saline and alkaline stresses on the germination, growth, photosynthesis, ionic balance and anti-oxidant system in an alkali-tolerant leguminous forage Lathyrus quinquenervius. Soil Sci. Plant Nutr. 2009, 55, 685–697. [Google Scholar] [CrossRef]
  4. Uddin, M.K.; Juraimi, A.S.; Ismail, M.R.; Hossain, M.A.; Othman, R.; Rahim, A.A. Effect of salinity stress on nutrient uptake and chlorophyll content of tropical turfgrass species. Aust. J. Crop Sci. 2011, 5, 620–629. [Google Scholar]
  5. Wei, L.X.; Lv, B.S.; Li, X.W.; Wang, M.M.; Ma, H.Y.; Yang, H.Y.; Yang, R.F.; Piao, Z.Z.; Wang, Z.H.; Lou, J.H.; et al. Priming of rice (Oryza sativa L.) seedlings with abscisic acid enhances seedling survival, plant growth, and grain yield in saline-alkaline paddy fields. Field Crops Res. 2017, 203, 86–93. [Google Scholar] [CrossRef]
  6. Yang, J. Development and prospect of the research on salt-affected soils in China. Acta Pedol. Sin. 2008, 45, 837–845. [Google Scholar]
  7. Feng, Y.J.; Zhang, W.; Chen, Q.; Ma, C.-H. Physico-chemical characteristics and microbial composition of saline-alkaline soils in Songnen Plain. Soils 2007, 39, 301–305. [Google Scholar]
  8. Chhabra, R. Classification of salt-affected soils. Arid Soil Res. Rehabil. 2004, 19, 61–79. [Google Scholar] [CrossRef]
  9. Bin, L.I.; Wang, Z.C.; Liang, Z.W.; Chi, C.M. Electrical conductivity and water quality evaluation of groundwater at sodic soil areas in the west of Jilin province. J. Agro-Environ. Sci. 2007, 26, 939–944. [Google Scholar]
  10. Huang, L.H.; Liang, Z.W. Ionic absorption characteristics of Leymus chinensis seeded in various pH soils. Chin. J. Grassl. 2008, 30, 35–39. [Google Scholar]
  11. Türkan, I.; Demiral, T. Recent developments in understanding salinity tolerance. Environ. Exp. Bot. 2009, 67, 2–9. [Google Scholar] [CrossRef]
  12. Flowers, T.J.; Colmer, T.D. Salinity tolerance in halophytes. New Phytol. 2008, 179, 945–963. [Google Scholar] [CrossRef] [PubMed]
  13. Chen, Y.; Shao, G.; Chang, R. The effect of salt stress on superoxide dismutase in various organelles from cotyledon of soybean seedling. Acta Agron. Sin. 1997, 23, 214–219. [Google Scholar]
  14. Zhu, D.F.; Cheng, S.H.; Zhang, Y.P.; Lin, X.Q.; Chen, H.Z. Analysis of status and constraints of rice production in the world. Sci. Agric. Sin. 2010, 73, 167–173. [Google Scholar]
  15. Koyama, M.L.; Yeo, A.R. Quantitative trait loci for component physiological traits determining salt tolerance in rice. Plant Physiol. 2001, 125, 406–422. [Google Scholar] [CrossRef] [PubMed]
  16. Lin, H.X.; Zhu, M.Z.; Yano, M.; Gao, J.P.; Liang, Z.W.; Su, W.A.; Hu, X.H.; Ren, Z.H.; Chao, D.Y. QTLs for Na+ and K+ uptake of the shoots and roots controlling rice salt tolerance. Theor. Appl. Genet. 2004, 108, 253–260. [Google Scholar] [CrossRef] [PubMed]
  17. Islam, M.R.; Salam, M.A.; Hassan, L.; Collard, B.C.Y.; Singh, R.K.; Gregorio, G.B. QTL mapping for salinity tolerance at seedling stage in rice. J. Sci. Food Agric. 2011, 23, 137–146. [Google Scholar] [CrossRef]
  18. Javed, M.A.; Huyop, F.Z.; Wagiran, A.; Salleh, F.M. Identification of QTLs for morph-physiological traits related to salinity tolerance at seedling stage in indica rice. Procedia Environ. Sci. 2011, 8, 389–395. [Google Scholar] [CrossRef]
  19. Wang, Z.; Chen, Z.; Cheng, J.; Lai, Y.; Wang, J.; Bao, Y.; Huang, J.; Zhang, H. QTL analysis of Na+ and K+ concentrations in roots and shoots under different levels of NaCl stress in rice (Oryza sativa L.). PLoS ONE 2012, 7, e51202. [Google Scholar] [CrossRef] [PubMed]
  20. Zheng, H.; Zhao, H.; Liu, H.; Wang, J.; Zou, D. Qtl analysis of Na+ and K+ concentrations in shoots and roots under NaCl stress based on linkage and association analysis in japonica rice. Euphytica 2015, 201, 109–121. [Google Scholar] [CrossRef]
  21. Ammar, M.H.M.; Pandit, A.; Singh, R.K.; Sameena, S.; Chauhan, M.S.; Singh, A.K.; Sharma, P.C.; Gaikwad, K.; Sharma, T.R.; Mohapatra, T.; et al. Mapping of QTLs controlling Na+, K+ and Cl− ion concentrations in salt tolerant indica rice variety CSR27. J. Plant Biochem. Biotechnol. 2009, 18, 139–150. [Google Scholar] [CrossRef]
  22. Pandit, A.; Rai, V.; Bal, S.; Sinha, S.; Kumar, V.; Chauhan, M.; Gautam, R.K.; Singh, R.; Sharma, P.C.; Singh, A.K. Combining QTL mapping and transcriptome profiling of bulked RILs for identification of functional polymorphism for salt tolerance genes in rice (Oryza sativa L.). Mol. Genet. Genom. 2010, 284, 121–136. [Google Scholar] [CrossRef] [PubMed]
  23. Sushma, T.; Krishnamurthy, S.L.; Vinod, K.; Balwant, S.; Rao, A.R.; Amitha, M.S.; Vandna, R.; Singh, A.K.; Singh, N.K. Mapping QTLs for salt tolerance in rice (Oryza sativa L.) by bulked segregant analysis of recombinant inbred lines using 50K SNP chip. PLoS ONE 2016, 11, e0153610. [Google Scholar]
  24. Qiao, K.; Takano, T.; Liu, S. Discovery of two novel highly tolerant NaHCO3 trebouxiophytes: Identification and characterization of microalgae from extreme saline-alkali soil. Algal Res. 2015, 9, 245–253. [Google Scholar] [CrossRef]
  25. Yu, Y.; Guan, L. Improving maize output through climate resources utilization. J. Anhui Agric. Sci. 2007, 35, 381–382. [Google Scholar]
  26. Li, Q.; Li, X.; Li, X.; Wang, Z.; Song, C.; Zhang, G. Sodium bicarbonate soil management and utilization in songnen plain. Resour. Sci. 2003, 25, 15–20. [Google Scholar]
  27. Wang, H.; Ahan, J.; Wu, Z.; Shi, D.; Liu, B.; Yang, C. Alteration of nitrogen metabolism in rice variety ‘nipponbare’ induced by alkali stress. Plant Soil 2012, 355, 131–147. [Google Scholar] [CrossRef]
  28. Lv, B.S.; Ma, H.Y.; Li, X.W.; Wei, L.X.; Lv, H.Y.; Yang, H.Y.; Jiang, C.J.; Liang, Z.W. Proline accumulation is not correlated with saline-alkaline stress tolerance in rice seedlings. Agron. J. 2015, 107, 51–60. [Google Scholar] [CrossRef]
  29. Ren, Z.H.; Gao, J.P.; Li, L.G.; Cai, X.L.; Huang, W.; Chao, D.Y.; Zhu, M.Z.; Wang, Z.Y.; Luan, S.; Lin, H.X. A rice quantitative trait locus for salt tolerance encodes a sodium transprter. Nat. Genet. 2005, 37, 1141–1146. [Google Scholar] [CrossRef] [PubMed]
  30. Li, Q.; Yang, A.; Zhang, W.H. Efficient acquisition of iron confers greater tolerance to saline-alkaline stress in rice (Oryza sativa L.). J. Exp. Bot. 2016, 67, 6431–6444. [Google Scholar] [CrossRef] [PubMed]
  31. Li, N.; Sun, J.; Wang, J.; Liu, H.; Zheng, H.; Yang, L.; Liang, Y.; Li, X.; Zou, D. QTL analysis for alkaline tolerance of rice and verification of a major QTL. Plant Breed. 2017, 136, 881–891. [Google Scholar] [CrossRef]
  32. Li, Q.; Yang, A.; Zhang, W.H. Comparative studies on tolerance of rice genotypes differing in their tolerance to moderate salt stress. BMC Plant Boil. 2017, 17, 141. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  33. Zhang, H.; Liu, X.L.; Zhang, R.X.; Yuan, H.Y.; Wang, M.M.; Yang, H.Y.; Ma, H.Y.; Liu, D.; Jiang, C.J.; Liang, Z.W. Root damage under alkaline stress is associated with reactive oxygen species accumulation in rice (Oryza sativa L.). Front. Plant Sci. 2017, 8, 1580. [Google Scholar] [CrossRef] [PubMed]
  34. Hossain, H.; Rahman, M.A.; Alam, M.S.; Singh, R.K. Mapping of quantitative trait loci associated with reproductive-stage salt tolerance in rice. J. Agron. Crop Sci. 2015, 201, 17–31. [Google Scholar] [CrossRef]
  35. Li, X.; Ma, L.; Bu, N.; Li, Y.; Zhang, L. Endophytic infection modifies organic acid and mineral element accumulation by rice under Na2CO3 stress. Plant Soil 2017, 420, 1–11. [Google Scholar] [CrossRef]
  36. Nguyen, H.M.; Sako, K.; Matsui, A.; Suzuki, Y.; Mostofa, M.G.; Ha, C.V.; Tanaka, M.; Tran, L.P.; Habu, Y.; Seki, M. Ethanol enhances high-salinity stress tolerance by detoxifying reactive oxygen species in Arabidopsis thaliana and rice. Front. Plant Sci. 2017, 8, 1001. [Google Scholar] [CrossRef] [PubMed]
  37. Liang, Y.P.; Jian, S.; Suo, Y.N.; Liu, H.L.; Wang, J.G.; Zheng, H.L.; Sun, X.X.; Zou, D.T. QTL mapping and QTL × environment interaction analysis of salt and alkali tolerance-related traits in rice (Oryza sativa L.). Sci. Agric. Sin. 2017, 50, 1747–1762. [Google Scholar]
  38. Takagi, H.; Tamiru, M.; Abe, A.; Yoshida, K.; Uemura, A.; Yaegashi, H.; Obara, T.; Oikawa, K.; Utsushi, H.; Kanzaki, E. Mutmap accelerates breeding of a salt-tolerant rice cultivar. Nat. Biotechnol. 2015, 33, 445–449. [Google Scholar] [CrossRef] [PubMed]
  39. Mardani, Z.; Rabiei, B.; Sabouri, H.; Sabouri, A. Identification of molecular markers linked to salt-tolerant genes at germination stage of rice. Plant Breed. 2014, 133, 196–202. [Google Scholar] [CrossRef]
  40. Sakina, A.; Ahmed, I.; Shahzad, A.; Iqbal, M.; Asif, M. Genetic variation for salinity tolerance in Pakistani rice (Oryza sativa L.) germplasm. J. Agron. Crop Sci. 2016, 202, 25–36. [Google Scholar] [CrossRef]
  41. Shi, Y.; Gao, L.; Wu, Z.; Zhang, X.; Wang, M.; Zhang, C.; Zhang, F.; Zhou, Y.; Li, Z. Genome-wide association study of salt tolerance at the seed germination stage in rice. BMC Plant Boil. 2017, 17, 92. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  42. Negrão, S.; Courtois, B.; Ahmadi, N.; Abreu, I.; Saibo, N.; Oliveira, M.M. Recent updates on salinity stress in rice: From physiological to molecular responses. Crit. Rev. Plant Sci. 2011, 30, 329–377. [Google Scholar] [CrossRef]
  43. Reddy, I.N.B.L.; Kim, B.K.; Yoon, I.S.; Kim, K.H.; Kwon, T.R. Salt tolerance in rice: Focus on mechanisms and approaches. Rice Sci. 2017, 24, 123–144. [Google Scholar] [CrossRef]
  44. Roy, S.J.; Negrão, S.; Tester, M. Salt resistant crop plants. Curr. Opin. Biotechnol. 2014, 26, 115–124. [Google Scholar] [CrossRef] [PubMed]
  45. Zhu, J.K. Regulation of ion homeostasis under salt stress. Curr. Opin. Plant Boil. 2003, 6, 441–445. [Google Scholar] [CrossRef]
  46. Genc, Y.; Mcdonald, G.K.; Tester, M. Reassessment of tissue Na(+) concentration as a criterion for salinity tolerance in bread wheat. Plant Cell Environ. 2007, 30, 1486–1498. [Google Scholar] [CrossRef] [PubMed]
  47. Babgohari, M.Z.; Niazi, A.; Moghadam, A.A.; Deihimi, T.; Ebrahimie, E. Genome-wide analysis of key salinity-tolerance transporter (HKT1; 5) in wheat and wild wheat relatives (A and D genomes). In Vitro Cell. Dev. Boil. Plant 2013, 49, 97–106. [Google Scholar] [CrossRef]
  48. Almeida, P.; Feron, R.; Boer, G.J.D.; Boer, A.H.D. Role of Na+, K+, Cl−, proline and sucrose concentrations in determining salinity tolerance and their correlation with the expression of multiple genes in tomato. AoB Plants 2014, 6, A354–A355. [Google Scholar] [CrossRef] [PubMed]
  49. Pires, I.S.; Negrão, S.; Oliveira, M.M.; Purugganan, M.D. Comprehensive phenotypic analysis of rice (Oryza sativa) response to salinity stress. Physiol. Plant 2015, 155, 43–54. [Google Scholar] [CrossRef] [PubMed]
  50. Bohnert, H.J.; Shen, B. Transformation and compatible solutes. Sci. Hortic. 1998, 78, 237–260. [Google Scholar] [CrossRef]
  51. Bohnert, H.J.; Nelson, D.E.; Jensen, R.G. Adaptations to environmental stresses. Plant Cell 1995, 7, 1099–1111. [Google Scholar] [CrossRef] [PubMed]
  52. Kumar, M.; Choi, J.; An, G.; Kim, S.R. Ectopic expression of OsSta2 enhances salt stress tolerance in rice. Front. Plant Sci. 2017, 8, 316. [Google Scholar] [CrossRef] [PubMed]
  53. Fu, R.; Zhang, M.; Zhao, Y.; He, X.; Ding, C.; Wang, S.; Feng, Y.; Song, X.; Li, P.; Wang, B. Identification of salt tolerance-related microRNAs and their targets in maize (Zea mays L.) using high-throughput sequencing and degradome analysis. Front. Plant Sci. 2017, 8, 864. [Google Scholar] [CrossRef] [PubMed]
  54. Xie, R.; Zhang, J.; Ma, Y.; Pan, X.; Dong, C.; Pang, S.; He, S.; Deng, L.; Yi, S.; Zheng, Y. Combined analysis of mRNA and miRNA identifies dehydration and salinity responsive key molecular players in citrus roots. Sci. Rep. 2017, 7, 42094. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  55. Kumar, M. Crop plants and abiotic stresses. Biomol. Res. Ther. 2013, 3, e125. [Google Scholar] [CrossRef]
  56. Kumar, M.; Gho, Y.S.; Jung, K.H.; Kim, S.R. Genome-wide identification and analysis of genes, conserved between japonica and indica rice cultivars, that respond to low-temperature stress at the vegetative growth stage. Front. Plant Sci. 2017, 8, 1120. [Google Scholar] [CrossRef] [PubMed]
  57. Wang, J.; Zhu, J.; Zhang, Y.; Fan, F.; Li, W.; Wang, F.; Zhong, W.; Wang, C.; Yang, J. Comparative transcriptome analysis reveals molecular response to salinity stress of salt-tolerant and sensitive genotypes of indica rice at seedling stage. Sci. Rep. 2018, 8, 2085. [Google Scholar] [CrossRef] [PubMed]
  58. Goswami, K.; Tripathi, A.; Sanan-Mishra, N. Comparative miRomics of salt-tolerant and salt-sensitive rice. J. Integr. Bioinform. 2017, 14, 1–15. [Google Scholar] [CrossRef] [PubMed]
Agronomy 08 00205 g001 550
Figure 1. Pot experiment in 2013. (A) Four rice variety plants’ performance in three kinds of potting mixture after 50 days from transplantation. The relative parameters (salt tolerance index) of growth and yield components of the four rice varieties in the (B) 2:1 potting mixture (C) 1:1 mixture. PHT represents plant height (cm), TN represents the number of tillers per plant, EPN represents the effective panicle number per plant, TGW represents the 1000-grain weight (g), SMP represents the spikelets of the main panicle, and NFS represents the number of filled spikelets. Values are means ± SD, n = 3. Different capital letters (A, B) and lowercase letters (a, b) on columns indicate significant differences at p < 0.01 and p < 0.05 based on Duncan’s test.
Figure 1. Pot experiment in 2013. (A) Four rice variety plants’ performance in three kinds of potting mixture after 50 days from transplantation. The relative parameters (salt tolerance index) of growth and yield components of the four rice varieties in the (B) 2:1 potting mixture (C) 1:1 mixture. PHT represents plant height (cm), TN represents the number of tillers per plant, EPN represents the effective panicle number per plant, TGW represents the 1000-grain weight (g), SMP represents the spikelets of the main panicle, and NFS represents the number of filled spikelets. Values are means ± SD, n = 3. Different capital letters (A, B) and lowercase letters (a, b) on columns indicate significant differences at p < 0.01 and p < 0.05 based on Duncan’s test.
Agronomy 08 00205 g001
Agronomy 08 00205 g002 550
Figure 2. Effects of saline–alkaline stress on Kitaake and Jiudao-66 seedlings. (A) Seedling performance. (B) Foliar chlorophyll concentration. Twenty-five-day-old rice seedlings grown in normal culture solution were transferred to a quarter of saline–alkaline soil leachate for 24 h and exposed to normal culture solution for a recovery period of five days. Bar = 10 cm. Foliar chlorophyll content was measured at the end of the stress treatment. Values are expressed as means ± SD, n = 3. Different letters (a, b) indicate significant differences between Kitaake and Jiudao-66 under the same treatment, as determined by a Student’s t-test (p < 0.05).
Figure 2. Effects of saline–alkaline stress on Kitaake and Jiudao-66 seedlings. (A) Seedling performance. (B) Foliar chlorophyll concentration. Twenty-five-day-old rice seedlings grown in normal culture solution were transferred to a quarter of saline–alkaline soil leachate for 24 h and exposed to normal culture solution for a recovery period of five days. Bar = 10 cm. Foliar chlorophyll content was measured at the end of the stress treatment. Values are expressed as means ± SD, n = 3. Different letters (a, b) indicate significant differences between Kitaake and Jiudao-66 under the same treatment, as determined by a Student’s t-test (p < 0.05).
Agronomy 08 00205 g002
Agronomy 08 00205 g003 550
Figure 3. (A,D) Effects of saline–alkaline stress on K+ concentration, (B,E) Na+ concentration, and (C,F) Na+/K+ ratio of shoots and roots in Kitaake and Jiudao-66 seedlings grown in normal and saline–alkaline stress conditions. Treatments and statistical analyses were as described in Figure 2. Different letters (a, b) indicate significant differences at p < 0.05.
Figure 3. (A,D) Effects of saline–alkaline stress on K+ concentration, (B,E) Na+ concentration, and (C,F) Na+/K+ ratio of shoots and roots in Kitaake and Jiudao-66 seedlings grown in normal and saline–alkaline stress conditions. Treatments and statistical analyses were as described in Figure 2. Different letters (a, b) indicate significant differences at p < 0.05.
Agronomy 08 00205 g003
Agronomy 08 00205 g004 550
Figure 4. (A,B) Proline and (C,D) soluble sugar content of shoots and roots of Kitaake and Jiudao-66 seedlings grown in normal and saline–alkaline stress conditions. Treatments and statistical analyses were as described in Figure 2. Different letters (a, b) indicate significant differences at p < 0.05.
Figure 4. (A,B) Proline and (C,D) soluble sugar content of shoots and roots of Kitaake and Jiudao-66 seedlings grown in normal and saline–alkaline stress conditions. Treatments and statistical analyses were as described in Figure 2. Different letters (a, b) indicate significant differences at p < 0.05.
Agronomy 08 00205 g004
Agronomy 08 00205 g005 550
Figure 5. (A,B) Total antioxidant capacity (T-AOC) and (C,D) malondialdehyde (MDA) content of shoots and roots of Kitaake and Jiudao-66 seedlings grown in normal and saline–alkaline stress conditions. Treatments and statistical analyses were as described in Figure 2. Different letters (a, b) indicate significant differences at p < 0.05.
Figure 5. (A,B) Total antioxidant capacity (T-AOC) and (C,D) malondialdehyde (MDA) content of shoots and roots of Kitaake and Jiudao-66 seedlings grown in normal and saline–alkaline stress conditions. Treatments and statistical analyses were as described in Figure 2. Different letters (a, b) indicate significant differences at p < 0.05.
Agronomy 08 00205 g005
Table
Table 1. Physical, chemical, and fertility characteristics of the three mixture types used in this experiment.
Table 1. Physical, chemical, and fertility characteristics of the three mixture types used in this experiment.
MixturesEC 1:5
μS·cm−1		TDS
ppm		pHOrganic
Matter %		Available
N mg·kg−1		Available P mg·kg−1Available K mg·kg−1CO32−
mg·kg−1		HCO3−
mg·kg−1		Na+
mg·kg−1		Cl−
mg·kg−1
Normal Soil (NS)22096.08.02.245.535.4164.0——195.041.057.0
2/3 NS1000445.08.81.566.532.2218.0192.0512.0181.0114.0
1/2 NS1498672.09.01.567.225.7229.0120.0976.0280.0497.0
Saline–Alkaline Soil (SAS)25401150.09.81.058.112.9272.0840.02562.0700.0398.0
Normal Soil (NS): NS:SAS = 1:0; 2/3 NS: NS:SAS = 2:1; 1/2 NS: NS:SAS = 1:1. Saline–Alkaline Soil (SAS): NS:SAS = 0:1. The saline–alkaline soil was collected at 0–30 cm depth of wild “barren” lands. Electrical conductivity (EC), total dissolved solids (TDS), and pH were determined under soil:water = 1:5; Organic matter, available N, K, and various ions were determined by industry standards “NY/T 1121.6-2006”, “LY/T 1229-1999”, “NY/T 889-2004”, and “LY/T 1251-1999”, respectively. Available P was determined with the Olsen-P method.
Table
Table 2. Survival rates of 72 rice variety seedlings in 2:1 potting mixture (NS:SAS = 2:1).
Table 2. Survival rates of 72 rice variety seedlings in 2:1 potting mixture (NS:SAS = 2:1).
Variety No.Survival
Rate %		Variety No.Survival
Rate %		Variety No.Survival
Rate %		Variety No.Survival
Rate %
D1097.78 ± 1.92D2888.89 ± 6.94D2577.78 ± 6.94D3158.89 ± 1.92
D7096.67 ± 3.33D4388.89 ± 3.85D2076.67 ± 3.33D4058.89 ± 1.92
D3696.67 ± 3.33D6388.89 ± 5.09D4576.67 ± 0.00D5258.89 ± 3.85
D3095.56 ± 5.09D387.78 ± 5.09D6076.67 ± 6.67D2456.67 ± 3.33
D5795.56 ± 3.85D1987.78 ± 1.92D6175.56 ± 1.92D1156.67 ± 3.33
D6895.56 ± 3.85D4687.78 ± 5.09D6275.56 ± 1.92D1456.67 ± 3.33
D194.44 ± 1.92D586.67 ± 3.33D1573.33 ± 6.67D5454.44 ± 5.09
D4794.44 ± 5.09D1786.67 ± 3.33D3373.33 ± 3.33D2253.33 ± 3.33
D7193.33 ± 3.33D2186.67 ± 6.67D4173.33 ± 3.33D5353.33 ± 0.00
D893.33 ± 5.77D3486.67 ± 0.00D2672.22 ± 5.09D3952.22 ± 5.09
D4993.33 ± 6.67D4286.67 ± 5.77D4472.22 ± 1.92D3751.11 ± 1.92
D6493.33 ± 5.77D6685.56 ± 1.92D1865.56 ± 5.09D450.00 ± 3.33
D2392.22 ± 5.09D5185.56 ± 5.09D4865.56 ± 5.09D650.00 ± 3.33
D3592.22 ± 3.85D6984.44 ± 1.92D3265.56 ± 1.92D1350.00 ± 0.00
D291.11±5.09D6784.44 ± 6.94D2964.44 ± 1.92D3848.89 ± 3.85
D2790.00±3.33D782.22 ± 5.09D5664.44 ± 1.92D6548.89 ± 1.92
D5090.00±0.00D1281.11 ± 5.09D5962.22 ± 5.09D5546.67 ± 3.33
D7290.00±3.33D5881.11 ± 5.09D961.11 ± 3.85D1645.56 ± 3.85
The data were collected after 30 days of transplanting. Values are means ± SD, n = 3.
Table
Table 3. Salt tolerance index of 36 rice varieties with respect to membership degree in the 2:1 potting mixture (NS:SAS = 2:1).
Table 3. Salt tolerance index of 36 rice varieties with respect to membership degree in the 2:1 potting mixture (NS:SAS = 2:1).
Variety No.MDVariety No.MDVariety No.MDVariety No.MD
D360.90D570.73D30.68D660.56
D680.88D10.73D630.68D50.53
D340.83D470.71D170.67D420.51
D300.81D430.71D230.67D510.50
D500.81D710.70D350.65D120.47
D270.79D490.70D20.64D690.47
D80.78D640.69D460.64D580.45
D100.76D720.68D210.62D670.45
D700.74D280.68D190.60D70.32
MD: membership degree.

Share and Cite

MDPI and ACS Style

Wang, H.; Takano, T.; Liu, S. Screening and Evaluation of Saline–Alkaline Tolerant Germplasm of Rice (Oryza sativa L.) in Soda Saline–Alkali Soil. Agronomy 2018, 8, 205. https://doi.org/10.3390/agronomy8100205

AMA Style

Wang H, Takano T, Liu S. Screening and Evaluation of Saline–Alkaline Tolerant Germplasm of Rice (Oryza sativa L.) in Soda Saline–Alkali Soil. Agronomy. 2018; 8(10):205. https://doi.org/10.3390/agronomy8100205

Chicago/Turabian Style

Wang, Hao, Tetsuo Takano, and Shenkui Liu. 2018. "Screening and Evaluation of Saline–Alkaline Tolerant Germplasm of Rice (Oryza sativa L.) in Soda Saline–Alkali Soil" Agronomy 8, no. 10: 205. https://doi.org/10.3390/agronomy8100205

APA Style

Wang, H., Takano, T., & Liu, S. (2018). Screening and Evaluation of Saline–Alkaline Tolerant Germplasm of Rice (Oryza sativa L.) in Soda Saline–Alkali Soil. Agronomy, 8(10), 205. https://doi.org/10.3390/agronomy8100205

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop