Growth and water status of cowpea under salt stress and exogenous melatonin applicationABSTRACT
Cowpea is a species considered sensitive to salt stress, with losses in growth and yield from the irrigation water electrical conductivity of 3.3 dS m⁻¹. Melatonin is a promising tool with an attenuating effect on abiotic stresses. Thus, this study aimed to evaluate the water status and growth of ‘BRS Tumucumaque’ cowpea as a function of irrigation water salinity and exogenous melatonin application. The experiment was conducted in a greenhouse, in a randomized block design, in a 3 × 3 factorial scheme, with three replicates and two plants in each experimental unit. The first factor consisted of three salinity levels in the irrigation water (0.5, 3.0, and 5.0 dS m⁻¹), and the second factor of three melatonin concentrations (0, 0.5, and 1 mM). At 41 days after sowing, plant height, stem diameter, number of leaves and leaflets, root length, leaf area, dry mass of leaves, petiole, stem and root, relative water content, electrolyte leakage, leaf mass per unit area and succulence were analyzed. Increasing salinity concentrations reduced most growth variables and increased electrolyte leakage. Exogenous application of melatonin did not have a significant effect on the attenuation of salt stress in cowpea.
Key words:
Vigna unguiculata (L.) Walp.; salinity; biostimulant; water relations; biomass production
HIGHLIGHTS:
Salinity significantly reduced the growth and accumulation of biomass of cowpea cv. BRS Tumucumaque.
The 0.5 mM melatonin concentration increased relative water content in cowpea irrigated with saline water.
Exogenous application of melatonin did not mitigate the deleterious effects of salinity on cowpea.
RESUMO
O feijão-caupi é uma espécie considerada sensível ao estresse salino, com perdas no crescimento e produtividade a partir da condutividade elétrica da água de irrigação de 3,3 dS m-1. O uso de melatonina tem se mostrado uma ferramenta promissora com efeito atenuador de estresses abióticos. Assim, o objetivo do estudo foi avaliar o crescimento e o status hídrico do feijão-caupi ‘BRS Tumucumaque’ em função da salinidade da água de irrigação e aplicação exógena de melatonina. O experimento foi conduzido em casa de vegetação, em delineamento em blocos casualizados, em esquema fatorial 3 × 3, com três repetições e duas plantas em cada unidade experimental. O primeiro fator foi constituído por três níveis de salinidade na água de irrigação (0,5; 3,0 e 5,0 dS m⁻¹); e o segundo fator, por três concentrações de melatonina (0, 0,5 e 1 mM). Aos 41 dias após a semeadura, foram analisadas a altura da planta, diâmetro do caule, número de folhas e de folíolos, comprimento radicular, área foliar e massa seca das folhas, pecíolo, caule e raiz, conteúdo relativo de água, extravasamento de eletrólitos, massa foliar por unidade de área e suculência. O aumento das concentrações de salinidade reduziu a maioria das variáveis de crescimento e aumentou o extravasamento de eletrólitos. A aplicação exógena de melatonina não teve efeito significativo na atenuação do estresse salino no feijão-caupi.
Palavras-chave:
Vigna unguiculata (L.) Walp.; salinidade; bioestimulante; relações hídricas; produção de biomassa
Introduction
Salinity in the soil compromises the availability of nutrients and reduces water infiltration, retention, and drainage, in addition to decreasing the soil’s organic matter content and microbial activity (Saber et al., 2024). In plants, salt stress negatively affects development and yield by causing ionic toxicity, nutritional imbalance, membrane lipid peroxidation, metabolic disturbances, and damage to the photosynthetic apparatus, which reduces photosynthesis and can lead to photoinhibition (Tabassum et al., 2024). In this context, it is essential to adopt sustainable strategies that promote the development of plants under adverse growing conditions.
Cowpea [Vigna unguiculata (L.) Walp.] is a crop of great global importance, serving as a staple food for millions of people (Nounagnon et al., 2024). Although classified as moderately tolerant to salinity, with a threshold of 3.3 dS m⁻¹ above which yield reductions may occur, cowpea still experiences morphological and physiological impairments due to salinity stress (Ayers & Westcot, 1999). According to Abiala & Sahoo (2022), salinity affects cowpea at almost all stages of development, from seed germination to final yield, causing reductions in seedling growth, pod formation, and total biomass.
A promising alternative is the use of biostimulants, which favor plant growth and increase plant resistance to stress (Silva et al., 2024). Melatonin, a natural biostimulant, has been used to mitigate salt stress in plants by promoting improvements in ionic homeostasis, enhancing photosynthesis, and reducing oxidative stress through the regulation of the expression of stress-related genes (Abd El-Ghany & Attia, 2020; Ahmad et al., 2023). Studies indicate that exogenous application of melatonin increases endogenous levels of this substance (Ding et al., 2018) and that, in both situations, the adverse effects of abiotic stresses are significantly mitigated (Ribeiro et al., 2024; Oliveira et al., 2025). This protective effect is largely attributed to melatonin’s regulation of antioxidant defense systems, enhancement of ionic homeostasis, osmotic adjustment, and the modulation of stress-related gene expression (Li et al., 2019). Specifically, melatonin boosts the activity of antioxidant enzymes such as superoxide dismutase and catalase, helps maintain Na⁺/K⁺ balance, and promotes the synthesis of compatible solutes, all of which contribute to mitigating salt stress in plants (Chaurasia et al., 2023).
In this context, it is essential to highlight the relevance of using sustainable technologies that promote plant growth and contribute to mitigating the effects of stress caused by adverse conditions. Thus, it is hypothesized that exogenous melatonin application improves growth and water relations of cowpea under saline conditions by enhancing osmotic adjustment and optimizing water use efficiency. Thus, this study aimed to evaluate the water status and growth of ‘BRS Tumucumaque’ cowpea as a function of irrigation water salinity and exogenous melatonin application.
Material and Methods
Cowpea plants, cultivar BRS Tumucumaque, were grown in a greenhouse from October to November 2023. The experiment was carried out in a greenhouse belonging to the Department of Agronomic and Forestry Sciences of the Universidade Federal Rural do Semi-Árido (UFERSA), located in Mossoró, RN, Brazil (5º 11’ 31” S, 37º 20’ 40” W, mean altitude of 18 m above sea level). According to Köppen’s classification, the region’s climate is of the BSh type (hot and dry) (Alvares et al., 2013), with an average annual rainfall of 673.9 mm. The average annual temperature is 27.4 ºC, and the average relative air humidity is 68.9% (Climate-Data, 2021). Daily data on air temperature and relative air humidity were recorded during the experiment using a digital thermo-hygrometer (Figure 1).
The experiment was conducted in a randomized block design, in the factorial scheme 3 × 3, with three replicates, totaling 27 experimental units (two plants in each experimental unit). The first factor evaluated three salinity levels in the irrigation water [0.5 (without stress), 3.0 (moderate stress) and 5.0 dS m⁻¹ (severe stress)], while the second considered three melatonin concentrations [0, 0.5, and 1 mM] (Ribeiro et al., 2024).
Each experimental unit consisted of two plants each one grown in a pot with a capacity of 2.6 dm³, filled with sieved soil and organic substrate in the proportion of 3:1 (v/v). The texture of the soil used was classified as loamy sand, with physical properties including 53% coarse sand, 29% fine sand, 13% silt, and 5% clay. The soil had a pH of 7.15, an electrical conductivity (EC) of 0.07 dS m⁻¹, and a cation exchange capacity (CEC) of 10.23 cmolc dm⁻³. The base saturation was 100%, and the aluminum saturation was 0%. Fertility values included 112.9 mg dm⁻³ of phosphorus, 1132.3 mg dm⁻³ of potassium, 214.6 mg dm⁻³ of sodium, 4.10 cmolc dm⁻³ of calcium, 2.30 cmolc dm⁻³ of magnesium, and 0.00 cmolc dm⁻³ of aluminum. The soil also had a sum of bases of 10.23 cmolc dm⁻³, an effective CEC of 10.23 cmolc dm⁻³, and an exchangeable sodium percentage of 1%. The area’s soil is classified as Ultisol (Soil Survey Staff, 2022).
Six cowpea seeds were sown directly in each pot. Seven days after sowing (DAS), thinning was performed, leaving one plant per pot. The salinity levels were prepared by adding sodium chloride (NaCl) to 60 dm³ of water to obtain saline solutions, except for the level of 0.5 dS m⁻¹, which was obtained using only supply water (Table 1). Until 15 DAS, plants were irrigated daily with non-saline water. After this period, saline treatments were initiated and maintained until the end of the experiment (41 DAS). Irrigation was conducted daily using the weighing lysimetry method, measuring the volume of evaporated or transpired water over 24 hours to maintain soil moisture at 80% of field capacity (Girardi et al., 2016).
Melatonin concentrations were prepared by dissolving the hormone in distilled water. The solutions were applied via foliar spray starting at 16 DAS and repeated weekly, totaling four applications (16, 22, 29, and 34 DAS). To ensure uniform coverage, all leaves were sprayed. Tween 80 adhesive (0.05% v/v) was added to the solutions to improve leaf adhesion.
At 41 DAS, the following growth variables were evaluated: plant height, stem diameter, number of leaves and leaflets, root length, leaf area and dry mass of leaves, petiole, stem and root. Plant height was measured with a ruler graduated in centimeters (cm); stem diameter was obtained with a digital caliper (accuracy of 0.01 mm) (model 500-752-20, Mitutoyo, Suzano, Brazil); the number of leaves and leaflets was counted manually; root length was measured with a ruler graduated in cm; leaf area was calculated from the scanning of all plant leaves, using ImageJ software to obtain the area of each leaf; and the dry mass of the plant parts (leaves, petiole, stem and root) was determined by weighing on a semi-analytical scale (precision of 0.01 g), after drying in a forced air circulation oven at 65 ºC for 72 hours, until reaching constant mass, where the results were expressed in g per plant.
With the values of leaf area and dry mass, the variables of specific leaf area (SLA), leaf area ratio (LAR), and leaf weight ratio (LWR) were determined, according to Benincasa (2003). The specific leaf area was calculated by the ratio between leaf area and leaf dry mass, expressed in cm² g⁻¹. The leaf area ratio was calculated by the ratio between leaf area and shoot dry mass, expressed in cm² g⁻¹. The leaf mass ratio was obtained by the ratio between leaf dry mass and total dry mass, expressed in g g⁻¹. In addition, the relative water content (RWC) (Irigoyen et al., 1992), electrolyte leakage (EL) (Lutts et al., 1996), leaf mass per unit area (LMA) and succulence (SUC) were evaluated, according to Mantovani (1999).
The data obtained were subjected to the Shapiro-Wilk normality test and Levene’s test for homogeneity of variances. Next, analysis of variance (F-test) was performed at p ≤ 0.05. When the results were significant, the means of the treatments were compared by Tukey’s test at p ≤ 0.05. Confbands were fitted for the variables evaluated over time (0, 7, 14 and 19 DAS), with 95% confidence intervals. In addition, principal component analysis (PCA) and Pearson’s correlation analysis were performed to verify the relationship between the variables analyzed. Pearson’s correlation coefficients were classified as follows: very weak (0 - 0.19); weak (0.20 - 0.39); moderate (0.40 - 0.79); strong (0.80 - 0.89) and very strong (0.90 - 1.00). The R statistical program analyzed the variables using the ‘FactoMineR’ and ‘factoextra’ packages (R Core Team, 2022).
Results and Discussion
Irrigation water salinity had a significant effect on number of leaflets, number of leaves, plant height, stem diameter, root length, leaf area, leaf area ratio, leaf weight ratio, leaf dry mass, stem dry mass, root dry mass, relative water content and leaf mass per unit area, specific leaf area, petiole dry mass, electrolyte leakage and succulence, indicating the negative influence on growth, biomass production and water status of the plants (Table 2). Melatonin concentrations showed significance only for the number of leaflets, stem diameter, root length, stem dry mass, petiole dry mass, and leaf mass per unit area (Table 2). However, a significant interaction was observed between the factors (salinity and melatonin) for stem dry mass, root dry mass, relative water content, leaf mass per unit area, and succulence (Table 2).
Salinity significantly influenced plant height and stem diameter. At the salinity level of 0.5 dS m⁻¹, plant height increased by 19.50, 27.46 and 31.04% at 7, 14 and 19 days after applying the treatments (DAAT), respectively (Figure 2A). On the other hand, at the salinity levels of 3.0 and 5.0 dS m⁻¹, plant height was reduced by 18.80 and 18.05%, respectively, when compared to the level of 0.5 dS m⁻¹ at 19 DAAT. Similar behavior was observed for stem diameter at the 0.5 dS m⁻¹ level, which showed increases of 20.25, 34.27 and 37.14% at 7, 14 and 19 DAAT, respectively (Figure 2C). However, there was slight variation over the days at the salinity levels of 3.0 and 5.0 dS m⁻¹ but a significant reduction in stem diameter was recorded at about 0.5 dS m⁻¹. On the other hand, the exogenous application of melatonin, regardless of the concentration used, did not promote significant changes in plant height (Figure 2B) or stem diameter (Figure 2D). These results indicate that, under the conditions evaluated, melatonin was ineffective in mitigating salinity’s adverse effects on these growth variables.
Plant height and stem diameter in response to saline water irrigation (A and C) and exogenous application of melatonin (B and D) in cowpea plants cv. BRS Tumucumaque, at different days after the start of treatments
The increase in salinity negatively affected the number of leaflets and leaves (Figure 3). At 19 days after the application of the treatments, the number of leaflets showed increases of 50.40 and 26.32% at the salinity level of 0.5 dS m⁻¹, compared to the levels of 3.0 and 5.0 dS m⁻¹, respectively (Figure 3A). Similarly, at the 0.5 dS m⁻¹ level, the number of leaves increased by 38.13 and 21.77% when compared to the 3.0 and 5.0 dS m⁻¹ levels, respectively (Figure 3C). The number of leaves reduced from 6.11 to 3.78 at the salinity levels of 5.0 and 0.5 dS m⁻¹ at 19 DAAT. On the other hand, melatonin concentrations did not promote significant changes in the number of leaflets (Figure 3B) or the number of leaves (Figure 3D). These results suggest that, under the conditions evaluated, melatonin was ineffective in mitigating salinity’s adverse effects on these variables.
Number of leaflets and number of leaves in response to saline water irrigation (A and C) and exogenous application of melatonin (B and D) in cowpea plants cv. BRS Tumucumaque, at different days after the start of treatments
Salinity impairs growth variables due to decreased nutrient availability and translocation to plant growth areas (Fu & Yang, 2023). This compromises plant height, stem diameter, number of leaves and biomass production during the crop cycle, as observed in Figure 4.
Cowpea plants cv. BRS Tumucumaque subjected to salinity levels in the irrigation water and melatonin concentrations
The increase in salinity resulted in significant reductions in plant height, stem diameter, number of leaves, and number of leaflets (Figure 5). At the level of 5.0 dS m⁻¹, the reductions in these variables were 27.32, 41.74, 45.18, and 56.60%, respectively, compared to the level of 0.5 dS m⁻¹ (Figures 5A, B, C, and D). No significant differences were observed between the salinity levels of 3.0 and 5.0 dS m⁻¹ for plant height, stem diameter and number of leaves. The observed reduction in growth traits can be attributed to salt stress-induced stomatal closure, a strategy plants adopt to minimize water loss. However, this mechanism reduces the input of CO₂, compromising the absorption of nutrients by leaf cells and resulting in a lower photosynthetic rate. Therefore, the growth and development of plants during the vegetative cycle are impaired (Turan et al., 2022). It is noteworthy that melatonin application did not significantly mitigate the negative effects of salinity on these growth variables. However, the application of 1.0 mM melatonin reduced stem diameter and number of leaflets compared to the control, indicating a possible inhibitory effect of melatonin on these traits under low salinity conditions (Figures 5B and C). This lack of response may be related to the high sensitivity of these traits to osmotic and ionic stress under saline conditions (Tabassum et al., 2024).
Plant height (A), stem diameter (B), number of leaflets (C), and number of leaves (D) in cowpea cv. BRS Tumucumaque subjected to salinity levels in the irrigation water and application of melatonin concentrations
Exogenous application of 1.0 mM melatonin reduced root length, while salinity also negatively affected this variable (Figure 6). As the salinity levels increased, a progressive reduction in root length was observed, with mean values of 17.09, 13.93 and 11.02 cm for the levels of 0.5, 3.0, and 5.0 dS m⁻¹, respectively (Figure 6). This reduction can be attributed to roots being highly sensitive to environmental stimuli, adjusting the direction and pattern of growth in response to adverse conditions (Lamers et al., 2020). In addition, changes in root growth are directly related to the severity of salt stress (Zou et al., 2022). Under high salinity conditions, it is common to observe a marked reduction in primary and lateral root length and the number of lateral roots as part of the adaptive response to salt stress (Yan et al., 2021).
Root length in cowpea plants cv. BRS Tumucumaque subjected to salinity levels in the irrigation water and melatonin concentrations
The dry mass of leaves, petioles, stems, and roots showed reductions of 67.25, 70.73, 68.37 and 83.11%, respectively, with the increase in salinity, especially at the level of 5.0 dS m⁻¹, compared to the level of 0.5 dS m⁻¹ (Figure 7). In addition, the application of 1.0 mM melatonin significantly reduced petiole dry mass (Figure 7B). However, the application of melatonin at a concentration of 0.5 mM promoted improvements in the dry mass of the stem and roots, with increments of 15.75 and 32.22%, respectively, at the salinity level of 0.5 dS m⁻¹ (Figures 7C and D). According to Kouam et al. (2021), dry mass loss is a typical response to salinity in cowpea, as root cells have difficulty absorbing water under salt stress due to the decreased osmotic potential of the surrounding soil. Consequently, there is impairment of metabolic activities, impairing growth and photosynthesis and, finally, resulting in a reduction in total dry mass (Sawariya et al., 2023).
Leaf dry mass (A), petiole dry mass (B), stem dry mass (C), and root dry mass (D) in cowpea plants cv. BRS Tumucumaque subjected to salinity levels in the irrigation water and melatonin concentrations
The leaf area of cowpea plants decreased with the increase in salinity, showing reductions of 30.39 and 47.50% for the salinity levels of 3.0 and 5.0 dS m⁻¹, respectively, compared to the level of 0.5 dS m⁻¹ (Figure 8A). On the other hand, the specific leaf area, leaf area ratio and leaf mass ratio increased with salinity intensity, with increments of 37.81, 42.88 and 8.33%, respectively, at the level of 5.0 dS m⁻¹ about 0.5 dS m⁻¹ (Figures 8B, C and D). Leaf area reduction is a typical response to salt stress, as Na⁺ and/or Cl⁻ accumulation in tissues interferes with plant metabolic processes, including photosynthesis (Balasubramaniam et al., 2023). This effect results in a lower production of photoassimilates, which compromises leaf growth and, consequently, total leaf area (Le et al., 2021).
Leaf area (A), specific leaf area (B), leaf area ratio (C), and leaf mass ratio (D) in cowpea cv. BRS Tumucumaque subjected to salinity levels in the irrigation water and melatonin concentrations
However, the increase in specific leaf area, leaf area ratio, and leaf mass ratio reflects the stress faced by the plant. Low values of specific leaf area are associated with salinity tolerance, as they indicate the accumulation of high levels of dry mass and secondary metabolites, giving the plant a greater capacity to withstand prolonged adverse conditions (Tabassum et al., 2017). The increase in leaf area ratio and leaf mass ratio under salt stress conditions is attributed to reduced leaf area, which minimizes water loss through transpiration, and to the accumulation of sodium and chloride ions in leaves, which can affect cellular homeostasis and leaf expansion as an adaptive response to stress (Amin et al., 2021). In addition, this increase may be related to the increase in mesophilic layers, favoring the thickening of the leaves (Jam et al., 2022).
The relative water content was significantly improved with exogenous melatonin application, especially at salinity levels of 3.0 and 5.0 dS m⁻¹, with increments of 24.44 and 37.57%, respectively, for the 0.5 mM concentration of melatonin compared to treatments without melatonin (Figure 9A). RWC is a crucial variable for assessing the plant’s ability to cope with stress conditions, reflecting its water status (El-Beltagi et al., 2023). The increase in RWC under salt stress conditions can be explained by the role of melatonin in ionic homeostasis (Li et al., 2019). Exogenous application of melatonin contributes to the regulation of plant water balance by enhancing the activity of plasma membrane H⁺-ATPases and Na⁺/H⁺ antiporters, which facilitate Na⁺ extrusion and K⁺ retention in root cells (Wang et al., 2013). This process helps maintain cellular osmotic balance, reduces ionic toxicity, and optimizes water uptake, improving plant tolerance to salinity.
Relative water content (A), electrolyte leakage (B), leaf mass per unit area (C), and succulence (D) in cowpea plants cv. BRS Tumucumaque subjected to salinity levels in the irrigation water and melatonin concentrations
Electrolyte leakage was intensified with the increase in salinity levels, with mean values of 26.43, 52.96, and 68.40% of damage to cell membranes at the levels of 0.5, 3.0, and 5.0 dS m⁻¹, respectively (Figure 9B). This increase is due to the toxicity caused by salinity, which compromises the integrity of cell membranes, favoring electrolyte leakage (Ekinci et al., 2021; Turan et al., 2022). The leaf mass per unit area was also affected by salinity, but the adverse effects were attenuated by concentrations of 0.5 and 1.0 mM of melatonin. These concentrations of melatonin promoted increments of 43.24 and 37.50% at the 5.0 and 3.0 dS m⁻¹ salinity levels, compared to the treatment without melatonin (Figure 9C). This increase can be attributed to melatonin’s protective role. Melatonin promotes salt tolerance by enhancing antioxidant enzyme activity, reducing oxidative stress, stabilizing cell membranes, and regulating ion homeostasis by modulating Na⁺/K⁺ balance (Chaurasia et al., 2023). These effects help mitigate salt-induced damage and increase plant biomass compared to control plants. In addition, the increase in leaf mass per unit area in response to salt stress may be related to the increase in leaf thickness and/or density, a typical adaptation of plants under adverse environmental conditions (Sancho-Knapik et al., 2021).
In treatments without the application of melatonin, the succulence was reduced with the increase in salinity, showing decreases of 31.26 and 41.09% at the levels of 3.0 and 5.0 dS m⁻¹, respectively, compared to the salinity level of 0.5 dS m⁻¹ (Figure 9D). However, at the salinity level of 5.0 dS m⁻¹ and for the concentration of 1.0 mM, an increase of 22.46% in succulence was observed compared to the treatment without melatonin. Succulence is a variable that reflects the storage of water in living cells and is a strategy for plants to accumulate water in tissues and dilute salts to tolerable concentrations (Chen & Wang, 2024). The observed increments in succulence under high salinity conditions can be attributed to the exogenous application of melatonin, which promotes ionic balance by regulating intracellular K⁺ and Ca²⁺ levels and improving the K⁺/Na⁺ ratio, contributing to plant tolerance to salt stress (Dadasoglu et al., 2022).
The sum of the principal components (PC1 and PC2) explained 87.7% of the total variance (Figure 10). PC1 contributed 77.4% of the total variation and exhibited positive correlations with the variables PH, SD, NL, NLF, RL, LDM, SDM, PDM, RDM and LA at the salinity level of 0.5 dS m-1 regardless of melatonin concentrations. In addition, the variables LAR, SLA, LMA, EL and RWC showed behaviors opposite to those of the growth variables, indicating that the increase in these variables negatively affects plant growth, especially with the increase in the intensity of salt stress. This behavior suggests that, under salinity conditions, plant adaptation involves changes in morphological and physiological characteristics that can compromise plant growth and development.
Principal component analysis (PCA) of the growth variables in cowpea plants cv. BRS Tumucumaque as a function of salinity levels in the irrigation water and application of melatonin concentrations
According to Pearson correlation analysis (Figure 11), electrolyte leakage showed strong negative correlations with the variables PH (-0.87), SD (-0.82), NL (-0.87), NLF (-0.88), LA (-0.82), SDM (-0.84) and very strong negative correlations with LDM, RDM and PDM, with values of -0.93, -0.90 and -0.90, respectively (Figure 11). This suggests that the increase in cell damage, reflected by the leakage of electrolytes, is inversely related to plant growth, especially in the dry mass of the different plant parts. In addition, the variables SLA, LAR, LWR and RWC also showed negative correlations, ranging from -0.39 to -0.95, indicating that the increase in variables such as leaf area ratio and succulence may be associated with an overall reduction in growth. On the other hand, the number of leaves showed very strong positive correlations with the variables PH (0.91), SD (0.95), RL (0.92), LA (0.95), LDM (0.97), SDM (0.92), RDM (0.96) and PDM (0.94). This behavior is explainable, because the increase in the number of leaves results in a more significant photosynthetic potential, which favors the production of photoassimilates and, consequently, the increase in the dry biomass of the plant. These results reinforce the importance of leaf number as a key indicator of plant photosynthetic capacity and its direct relationship with growth and dry matter accumulation.
Pearson’s correlation analysis between the growth variables and water relations in cowpea plants cv. BRS Tumucumaque, as a function of salinity levels in the irrigation water and application of melatonin concentrations
Conclusions
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Exogenous application of melatonin does not mitigate the damage caused by salt stress in cowpea cv. BRS Tumucumaque.
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The increase in salinity had a negative effect on the growth and water status of cowpea plants.
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Relative water content was improved at moderate and severe salinity when plants were treated with a concentration of 0.5 mM melatonin.
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1 Research developed at Universidade Federal Rural do Semi-Árido, Mossoró, RN, Brazil
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Supplementary documents
There are no supplementary sources.
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Financing statement
This study was funded by the Coordination for the Improvement of Higher Education Personnel - Brazil (CAPES) - Financing Code 001, and National Council for Scientific and Technological Development - Brazil (CNPq).
There are no supplementary sources.
Shaded areas represent the 95% confidence intervals
Shaded areas represent the 95% confidence intervals
Means followed by the same letters above the columns do not differ for salt stress, and means followed by the same letters in the legend do not differ from each other for melatonin according to the Tukey’s test (p ≤ 0.05); CV - Coefficient of variation; Vertical bars represent one standard error of the mean (n = 3)
Means followed by the same letters above the columns do not differ for salt stress, and means followed by the same letters in the legend do not differ from each other for melatonin according to the Tukey’s test (p ≤ 0.05); CV - Coefficient of variation; Vertical bars represent one standard error of the mean (n = 3)
Means followed by the same letters above the columns do not differ for salt stress, and means followed by the same letters in the legend do not differ from each other for melatonin according to the Tukey’s test (p ≤ 0.05) (A and B); Means followed by the same lowercase letters are not significantly different for melatonin, while means followed by the same uppercase letters show no significant differences for salt stress, according to Tukey’s test (p ≤ 0.05) (C and D); CV - Coefficient of variation; Vertical bars represent one standard error of the mean (n = 3)
Means followed by the same letters above the columns do not differ for salt stress, and means followed by the same letters in the legend do not differ from each other for melatonin according to the Tukey’s test (p ≤ 0.05); CV - Coefficient of variation; Vertical bars represent one standard error of the mean (n = 3)
Means followed by the same lowercase letters are not significantly different for melatonin, while means followed by the same uppercase letters show no significant differences for salt stress, according to Tukey’s test (p ≤ 0.05) (A, C and D); Means followed by the same letters above the columns do not differ for salt stress, and means followed by the same letters in the legend do not differ from each other for melatonin according to the Tukey’s test (p ≤ 0.05) (B); CV - Coefficient of variation; Vertical bars represent one standard error of the mean (n = 3)
PH - Plant height; SD - Stem diameter; NLF - Number of leaflets; NL - Number of leaves; RL - Root length; LA - Leaf area; SLA - Specific leaf area; LAR - Leaf area ratio; LWR - Leaf weight ratio; LDM - Leaf dry mass; SDM - Stem dry mass; RDM - Root dry mass; PDM - Petiole dry mass; RWC - Relative water content; EL - Electrolyte leakage; LMA - Leaf mass per unit area; SUC - Succulence. The numbers after the letter “E” correspond to the salinity levels. The numbers after the letter “M” correspond to melatonin concentrations
