Salt Stress on Cotton Plant | Encyclopedia MDPI

Salt Stress on Cotton Plant: History

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Subjects: Agricultural Economics & Policy

Contributor:

Aqsa Ijaz

Sana Muhy-Ud-Din Khan

Sajjad Haidar

Hafiz Mumtaz Hassan

Muhammad Kashif Riaz Khan

Cotton plants are affected in multiple ways by salt stress, including diminished growth, limited leaf area expansion, and impaired nutrient uptake. The accumulation of cytoplasmic Na⁺ and Cl^- ions, which can lead to cell death, is also a consequence of salt stress. Plant salt stress is a phenomenon that occurs when soil solution contains an excessive amount of salts, leading to the inhibition of plant growth or even death.

salt tolerance
cotton
marker-assisted selection
genotyping by sequencing

1. Introduction

Plant biofibers are extremely valuable in terms of economics and trade. The most important fiber-producing crops are cotton (Gossypium hirsutum L.), jute (Corchorus capsularis L.), kenaf (Hibiscus cannabinus L.), flax (Linum usitatissimum L.), and hemp (Cannabis sativa L.) [1,2]. The fibers produced from these plants are of excellent quality and have a high economic value globally [3,4]. Cotton, the most significant crop, serves as the foundation of the textile sector [5,6]. Both cotton fiber and seed have commercial applications [7]. Cotton byproducts are used for a variety of purposes, including as oil, feed, food products, biofuels, and textile materials [8,9].

Climate change has resulted in increased soil salinity [10]. The rise in sea level due to climate change has increased salinity in soil by up to 33 percent from the last 25 years [11,12,13]. Global warming is increasing, resulting in glaciers and ice sheets melting, and the thermal expansion of sea water leads to a rise in sea levels. The obvious outcomes of a rising level are flooding and increased salinity. The latter is seen in increasing salinity in ground as well as surface water via mixing saltwater with fresh water. Salinity is more common in arid regions than in semi-arid regions [14,15]. Heavy/low rainfall and repeated drought conditions have been common because of shifts in weather. Both excessive and insufficient rainfall can influence soil salinity. Abundant rainfall can lower the concentration of salts in the soil by diluting them, resulting in decreased salinity. This is because the rainwater rinses away some of the salt in the soil, creating a less concentrated solution. Conversely, insufficient rainfall can cause an increase in salinity. This is because the salt in the soil is not washed away, resulting in the accumulation of salt over time. Typically, soil salinity is more likely to rise in arid regions with limited rainfall or in locations where the water table is high, enabling saltwater to seep into the soil. The water moves upward and increases salt in the root zone areas of coastal and shallow water table regions. Moreover, soil salinity is affected by periodic episodes of temperature as well as rainfall [16].

Salt stress is the second most prevalent abiotic stress after drought, impairing plant growth and reducing agricultural production worldwide [17,18]. Plant salt stress is a phenomenon that occurs when soil solution contains an excessive amount of salts, leading to the inhibition of plant growth or even death. On a global level, excess salt is the most significant factor that inhibits plant growth. This condition can hinder the absorption of vital nutrients and water required for plant growth, resulting in stunted growth and lower yields [19,20,21]. It can also inflict harm on plant roots, leaves, and other organs, decrease photosynthesis, and disturb the plant’s metabolism [22,23,24].

The world is facing a concerning issue of declining arable land, which has led to heightened competition for grain and fiber crops [7,25]. However, the presence of salts in these soils poses challenges to cotton growth and development, as it disrupts crucial physiological and biochemical processes [26,27]. Moreover, the early developmental stages of cotton are particularly vulnerable to salt stress, which has a significant impact on eventual crop output [28].

Due to poor management practices and lack of regulation, salt stress is getting worse every year. Saline irrigation increases the amount of sodium chloride in the soil, which can lead to soil degradation [28]. Cotton plants are affected in multiple ways by salt stress, including diminished growth, limited leaf area expansion, and impaired nutrient uptake. The accumulation of cytoplasmic Na⁺ and Cl^- ions, which can lead to cell death, is also a consequence of salt stress [13]. Furthermore, it can decrease the activity of metabolic enzymes, contributing to the deterioration of fiber quality [29].

2. Impacts and Responses of Salt Stress on Cotton Plant

A potential avenue for improving cotton performance in saline environments could involve gaining an understanding of how cotton responds to salt, its resistance mechanisms, and effective management approaches. This knowledge could inform the development of strategies to enhance cotton growth and yield in such environments [34].

Salt stress decreases biomass production, stem thickness, reduction in leaf area, root and shoot weight, and yield of seed [35]. Cotton yield decreases at a salinity level of 7.7 dS m⁻¹, and a 50% reduction in output was noted at 17.0 dS m⁻¹ [36]. Under salt stress, fiber strength, length, and micronaire values decrease in both Gossypium hirsutum and Gossypium barbadense, but ginning out-turn increases. However, this increase is accompanied by a decrease in fiber strength, length, and micronaire values in both Gossypium hirsutum and Gossypium barbadense [35]. In addition, salt stress also decreases the photosynthetic activity and percentage of carotenoid contents, ultimately resulting in poor plant growth. Compared to later stages, salt stress is more detrimental to the germination, emergence, and seedling phases [30]. Salt stress can lead to delayed flowering, a decrease in the number of flowers per plant, an increase in fruit shedding, and a reduction in boll weight. Under salt stress, the concentration of Na⁺ and Cl⁺ increases by decreasing the K⁺, Ca²⁺, and Mg²⁺ concentration in cotton leaves. Increasing certain ions can decrease other ions due to competition for uptake by the plant. When a plant is exposed to high concentrations of some ions, such as sodium and chloride ions, they compete with other ions, such as potassium and magnesium, for uptake by the plant. This can result in decreased uptake of the other ions, leading to a decrease in their concentrations in the plant. This competition between ions for uptake is known as ionic competition and can have a significant effect on the overall ion concentrations in the plant [37].

Na⁺ exclusion has commonly been attributed to salt tolerance in cotton. Cotton is affected by high salinity, resulting in reduced uptake of potassium (K) and nitrogen (N), whereas low salt levels have minimal impact on their absorption [35]. Reduction of metabolic enzyme activity, such as alkaline invertase, sucrose phosphate synthase, and acidic invertase results in low fiber quality under salt stress. For example, Peng and others in 2016 discovered that in two different cotton cultivars, high soil salinity hindered cellulose synthesis, decreased the rate of sucrose conversion, and affected the functions of sucrose-metabolizing enzymes [38].

2.1. Impact of Salt Stress on Cotton Growth

To address the salt stress issue, it is important to comprehend how salt affects cotton at various growth stages.

2.1.1. Root and Shoot

Salt stress is more common in cotton at germination, emergence, and young seedling stages [35]. However, salt stress is more sensitive in seedlings at germination stage than in seedlings at the juvenile stage [34]. A significant reduction in cotton production occurs when there is a decrease in the plant population due to poor germination [39]. The growth of roots is impeded by salt stress as it decreases the number of secondary roots and diminishes the length of roots [40]. Primary root length is reduced with high salt concentration, while secondary root length is similarly slowed by modest salt stress [41]. Root growth is variably reduced according to soil type as salt stress increases. The effects are more obvious in clay and loam soils than in sandy soils [42]. High salt stress has a detrimental impact on vegetative development. Salt stress lowers the ratio of shoots to roots, indicating that shoot growth is more susceptible to salt stress as compared to root growth [34]. Studies conducted at different stages of cotton growth have found that the six-leaf stage is particularly susceptible to the negative impacts of salt stress [43].

2.1.2. Boll Development and Yield

As salt stress increases, cotton yields decrease drastically, which is evidenced by a decrease in the number of bolls and their weight. Furthermore, a reduction in the number of fruit-bearing positions, a delay in blooming, an increase in flowers shedding, and a decrease in the number of bolls per plant due to salt stress all contribute to a reduction in mature bolls [34]. Detrimental impacts of high salt stress on vegetative development eventually delay flowering and might also cause a delay in flower blooming. Irrigating cotton with highly saline water during the budding stage can result in a yield reduction of approximately 90 percent [34].

2.1.3. Fiber Quality

Fiber quality traits are genetically controlled but are influenced by the environment [44,45]. Fiber length, strength, and maturity are all reduced under salt stress, whereas fiber fineness increases. It has been reported that when the Na⁺ ion percentage is increased, it negatively affects the fiber length, strength, and micronaire values [37,46]. In salt-sensitive cultivars, cellulose content and sucrose transformation rate both dropped considerably with an increase in NaCl level, resulting in fiber quality degradation. Sucrose is accessible in a saline environment, but due to reduced activity of metabolic enzymes such as sucrose phosphate synthase, acidic invertase, and alkaline invertase, it is not effectively transformed into cellulose [38]. Table 1 represents the findings of salt stress effects during various growth stages in cotton.

Table 1. Impact of salt stress on different developmental stages of cotton.

Species	Variety	Experimental Condition	Stress Applied	Stress Duration	Salt Stress Effect on Cotton	References
Gossypium hirsutum L.	Xinluzao13 and Klebsiella oxytoca Rs-5	Pot	5 g NaCl	4 weeks	Reduced germination rate	[47]
Gossypium barbadense L.	Giza 90	Pot	Diluted sea water	10 days	Reduced growth	[48]
Gossypium hirsutum L.	GXM9	Petri dishes	150 Mm NaCl	6 days	Reduced germination	[49]
Gossypium hirsutum L.	9807 and Z010	Hydroponic culture	150 Mm NaCl	14 days	Reduction in growth	[50]
Gossypium hirsutum L.	Guoxin No.9	Hydroponic culture	150 Mm NaCl	12 days	Decreased plant height	[51]
Gossypium hirsutum L.	−	Pot	150 Mm NaCl	40 days	Growth Reduction	[52]
Gossypium hirsutum L.	BRS Topázio, BRS Safira, BRS Rubi	Pot	90 Mm NaCl	Vegetative and Flowering stage	Reduction in fiber quality and yield	[53]
Gossypium hirsutum L.	Nongfeng 133	Barrel Planting	7.3 g kg⁻¹ salt stress	6 months	Reduced boll number and size	[49]
Gossypium barbadense L.	Giza 45	Mini-rhizotron System	150 Mm NaCl	Two Weeks	Reduced root length	[54]
Gossypium hirsutum L.	Nongfeng 133	Field	Brakish water irrigation	Throughout study	Reduced yield	[55]
Gossypium hirsutum L.	IR-NIBGE-13 and BS-2018	Pot	200 Mm NaCl	One week	Reduced plant biomass	[5]
Gossypium hirsutum L.	Xinluzao 52	Field	NaCl and CaCl₂ (8.04 dS m⁻¹)	30 days	Reduction in biomass	[56]
Gossipyum barbadense L.	−	Pot	Diluted sea water (EC = 52 dS m⁻¹)	Throughout study	Decreased boll weight	[57]
Gossypium hirsutum L.	C-6524	Petri dishes	100 Mm NaCl and 100 Mm Mg₂So₄	5 days	Low germination	[58]
Gossypium hirsutum L.	Zhongmian 41	Hydroponic system	150 mM NaCl	20 days	Reduced plant growth	[59]
Gossypium hirsutum L.	CCRI 35, Z 51504 and CCRI 49	Pot	150 mM NaCl	9 days	Reduced shoot dry weight	[60]
Gossypium hirsutum L.	Simian 3	Pot	150 mM NaCl	30 days	Reduced plant biomass	[61]
Gossypium hirsutum L.	CCRI-79 and Simian 3	Field	11.46 dS m⁻¹ Soil salinity	Throughout study	Reduced fiber quality	[38]
Gossypium hirsutum L.	Lu-mian-yan No. 24 and Xin-lu-zao No. 45	Pot	0.4% NaCl	Throughout study	Decreased biomass	[62]
Gossypium hirsutum L.	Zhong 07 and Zhong G5	Hydroponic system	200 mM NaCl	48 h	Stem binding	[62]
Gossypium hirsutum L.	Xinluzhong-37	Pot	150 mM NaCl	35 days	Reduced growth	[63]
Gossypium hirsutum L.	−	Pot	400 mM NaCl	12 h	Inhibited growth	[64]
Gossypium hirsutum L.	−	Field	Salt affected soil < 7.7 dS m⁻¹.	Throughout study	Poor seedling emergence and fiber yellowness	[65]
Gossypium hirsutum L.	NIAB 777	Pot	NaCl (17 dS m⁻¹)	40 days	Decreased plant height	[66]
Gossypium hirsutum L.	−	Paper germination test	250 mM NaCl	12 days	Poor germination rate, reduced seedling growth	[67]

2.2. Response of Cotton Plant to Salt Stress

Under conditions of salt stress, soluble salts accumulate in the root zone of cotton, leading to the development of osmotic and ionic stress, as well as disturbances in mineral balance [68], which result in a severe decrease in crop quality and production [69]. Because of osmotic, ionic, and oxidative stressors, salt stress severely affects cotton growth, development and production. As a result, identifying and developing cotton cultivars that can withstand salt stress is a major challenge for sustainable agriculture [70].

Cotton’s most effective response to salt stress either excludes excess sodium or compartmentalization. There is significant potential to create salt-tolerant cotton cultivars by boosting enzymatic and nonenzymatic antioxidant gene expression. Additionally, priming seeds is an efficient method for enhancing cotton germination in saline soils [34].

Seed priming is an economical method of hydrating seeds and promoting rapid, uniform germination. This technique results in reduced imbibition time, increased metabolic activity, and osmotic adjustment. It also triggers molecular changes such as DNA synthesis, protein production, and the accumulation of antioxidants. There are various types of priming methods, including hydropriming (presoaking in water with or without drying), osmopriming (soaking in osmotic solutions such as sugar or mannitol followed by air drying), and hormopriming (soaking in hormone solutions such as auxin or gibberellic acid). These methods have been reviewed in multiple studies [71].

Zhang and fellows in 2021 divulged that melatonin priming can enhance the salt tolerance of Gossypium hirsutum L. (cotton) seedlings under salt stress conditions. According to the study, seedlings that were cultivated from seeds primed with 25 mM melatonin displayed greater root and shoot biomass and increased ion accumulation in comparison to the control group. These results suggest that melatonin priming has a beneficial effect on salt stress tolerance. The study also concluded that melatonin-primed seedlings performed better under saline conditions compared to nonprimed seedlings, indicating the potential for melatonin priming to enhance salt tolerance in cotton plants [69].

Shaheen and colleagues (2015) found that seed priming with KNO₃ (1.5%) was found to reduce salt stress in cotton seedlings, improving dry matter and nutrient uptake, as well as shoot and root lengths, biomass, and cation (Ca²⁺, Na⁺, and K⁺) accumulation [72]. Wang and others (2021) also demonstrated that Mepiquat chloride-priming positively improve cotton seed germination and seedling establishment when exposed to salt stresses [73]. According to the report by Ahmadvand and fellows (2012), the priming of cotton seeds with KNO₃ resulted in improved germination and seedling growth even when subjected to salt stress [74].

Utilizing marker-assisted selection (MAS) and exploiting the inter- and intravariation in cotton germplasm can be effective in generating salt-resistant variants. Additionally, a transgenic approach could serve as a crucial tool for cultivating cotton in saline conditions. Transgenic approaches involve transferring specific genes from one organism to another in order to achieve desired characteristics. Transgenic methods are quicker than traditional breeding techniques and can enable crossing of genera boundaries. Through the transfer of salt-responsive genes from other sources, transgenic approaches have been utilized to create salt-resistant plants. This technology has already demonstrated successful implementation in cotton [34].

Research studies have shown that the introduction of TsVP, a gene for H⁺-PPase from Thellungiella halophilla, into transgenic cotton plants can enhance their root and shoot growth, as well as their photosynthetic activity under high salt stress conditions [75]. This is likely the result of TsVP aiding the storage of Na⁺ and Cl⁻ in the vacuoles, which leads to a decrease in membrane ion leakage and malondialdehyde levels [75]. Expressing the TsVP gene from Thellungiella halophila can enhance cotton emergence, survival, and fiber quality under high saline conditions, while expression of the AVP1 gene from Arabidopsis thaliana improves growth and fiber yield in salt-stressed transgenic cotton. Co expression of AtNHX1 and TsVP genes in cotton also boosts emergence rate and yield under high saline environments [76]. In the future, researchers may utilize a combination of conventional techniques and state-of-the-art molecular technologies to breed salt-tolerant plant varieties [34].

There is substantial inter- and intraspecific variation in cotton salt tolerance, which is critical for selection and breeding regarding salt stress [43]. In the context of saline stress, the process of ion exclusion, specifically the exclusion of Na⁺/Clˉ, is accountable for the uptake and storage of detrimental ions within the tissues of cotton [68]. Several studies have shown that increased levels of K⁺/Na⁺ and Ca²⁺/Na⁺ in cotton tissues are associated with greater tolerance to saline stress. For instance, Kumar and colleagues in 2020 observed varying levels of inorganic sodium (Na⁺) accumulation in different cotton genotypes. The salt tolerant genotypes displayed higher potassium (K⁺)/sodium (Na⁺) ratios than their salt-sensitive counterparts [70]. Zafar and others during 2020 and 2021 discovered that tolerant cotton genotypes were able to maintain a stable potassium-to-sodium ratio in comparison to salt-sensitive cotton genotypes [27]. In 2003, Ahmad and colleagues conducted a study to investigate the effect of the calcium-to-sodium ratio for salt tolerance in plants. They reported that salt tolerant genotypes exhibited higher calcium-to-sodium ratios in their leaves than salt sensitive ones under saline conditions. The outcomes of the study indicate that calcium may have a pivotal function in the maintenance of proper membrane function and the regulation of its permeability, leading to normal growth in salt tolerant varieties in contrast to salt sensitive ones [77].

Consequently, this parameter can serve as a selection criterion for screening salt tolerant varieties. Genotypes demonstrating elevated antioxidant activity under saline conditions can be considered more tolerant to salt stress [78]. Genetic analysis of growth, fiber characteristics and yield under salt stress have shown to be genetically regulated via different quantitative trait loci (QTLs). Larger genetic additive variance of these traits can be utilized in cotton breeding programs for salt tolerance [79].

This entry is adapted from the peer-reviewed paper 10.3390/genes14051103

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