The sesame crop is usually avoided in salt-affected areas because of the various effects of saline stress on plants. Besides varying between species, salinity effects are known to vary for genotypes of the same species as well as plant development stages. Thus, through the irrigation of plants with saline water, this study evaluates tolerance to saline stress of new sesame genotypes in different phenological stages. Three experiments were carried out under greenhouse conditions, using the sesame genotypes BRS Seda, LAG-927561 and LAG-26514. Water with different levels of electrical conductivity (ECw = 0.6, 1.6, 2.6, 3.6 and 4.6 dS m - 1 ) was used to irrigate plants during germination and initial growth stages, as well as the entire crop cycle. Tolerance to saline stress (3.6 dS m - 1 ) during growth and production stages was also studied. Salinity did not affect sesame germination, but seedling growth was hindered from the ECw of 1.6 dS m - 1 onwards, and plant height was the most affected growth variable. Seed production is affected by salinity, regardless of the phenological stage in which plants are exposed to salinity. The strains LAG-927561 and LAG-26514 show promising signs in studies on adaptation to saline stress.
The sesame crop (Sesamum indicum L.) has stood out among oilseed plants due to the commercial importance of its seeds, their fresh consumption, the food industry and oil production. Rich in antioxidants, sesame oil is also notable for its resistance to oxidation, which is higher than in other species [
Sesame is the earliest oilseed plant to be used by humans [
For agricultural production in arid and semi-arid areas, a relevant aspect to be considered is the salinity of soils and water resources, aspects that are common in many regions worldwide [
In general, plant capacity to adjust to saline stress varies widely as variation can occur between cultivars using the same species and between phenological stages of the same genotype [
Bahrami and Razmjoo [
It should be pointed out that, in addition of divergent, the results for the effects of salinity on sesame in the available literature are scarce and there is no information on the phenological stage in which plants are most sensitive to salt effects. In this context, this study evaluates the effects of salinity on sesame plants in different development stages in order to identify the genotypes that best adapt to this stress factor.
Three experiments were carried out under greenhouse conditions in Campina Grande, PB, Brazil (7˚15'18''S; 35˚52'28''O; altitude of 550 m). The greenhouse was covered with plastic of agricultural use and laterally protected by a fine mesh screen. According to Köppen’s classification, the climate of the region is “Csa”, with hot, dry summer and rains in the autumn and winter [
Two white-seeded sesame genotypes, the variety BRS Seda (Brazil Seeds) and the strain LAG-927561 (LAG-Advanced Sesame Strain, called Branquinha)―and a black-seeded strain LAG-26514, called Pretinha were used for the experiments.
The Sesame cultivar BRS Seda was obtained through mass selection applied in cv. Zirra FAO 51284, and the advanced strain LAG is originated from the access PI 231034-USDA. In both cases, there was a selection pressure for white seeds. The seeds of the advanced strain LAG-26514 are black in color, originating from the access PI 200109-USDA. The plants of the three genotypes are of medium height and early cycle, with seed oil content between 50% and 52%. They are recommended for cultivation in sandy soils (pH = 5,5 - 7.0), with altitude of up to 1250 m, air temperatures between 23˚C - 30˚C, and pluviosity of 300 mm, well distributed during the cultivation cycle.
The seeds were provided by the Brazilian Agricultural Research Corporation (National Center of Cotton Research), located in Campina Grande, PB. All seeds were collected in the same period, under the same cultural management practices, selected before seeding and treated with a dicarboximide fungicide (240 g per kg−1 of seeds).
Humidity in the substrate was maintained at field capacity during seeding. Three seeds were planted in each recipient at a depth of 1 cm. After seedling emergence, thinning was performed 11 days after seeding (DAS), leaving only one plant per recipient. Throughout all the experimental phase there was control of weeds and insects and diseases.
The treatments varied in each experiment and consisted of different managements of salinity water irrigation according to the phenological phases of the plants. Saline water composition was obtained using the salts NaCl, CaCl2∙2H2O and MgCl2∙6H2O, maintaining a proportion of 7:2:1 for Na:Ca:Mg. This ratio prevails in water sources used for irrigation in most small farms of Northeast Brazil [
In this experiment the treatments comprised of 5 levels of electrical conductivity for the irrigation water (ECw = 0.6, 1.6, 2.6, 3.6 and 4.6 dS m−1, at 25˚C), set in a randomized block design, with four replications and 10 evaluated plants in each plot.
Plants were cultivated in 280-mL polyethylene tubes, filled with 300 g of a commercial humus-based organic compound (70%), plant residues (20%) and cattle manure (10%). Plants were irrigated daily from 8 to 9 AM with saline water according to the ECw levels of the treatments. The volume of water applied in each irrigation event (Vi) was estimated based on the replenishment of the volume consumed in the previous day, ensuring a leaching fraction of 20% (Equation (1)), in order to maintain part of the salts from the irrigation water accumulated in the root zone. The leached volume was estimated with the aid of recipients placed below the tubes.
Vi = volume to be applied in the next irrigation event (mL); Va = volume applied in the irrigation of the previous day (mL); Vd = volume drained (mL); and Lf = leaf fraction: it was used a coefficient of approximately 20% (1 - 0.20).
This experiment lasted until 26 DAS, when a final evaluation was done. The number of seedlings that emerged in each plot was recorded daily in order to evaluate germination percentage (GP) and considered plants that emerged on the surface of the substrate. The germination speed index (GSI) was obtained by measuring the relationship between the number of seedlings that emerged in each plot and the number of days elapsed of the respective count [
Plant growth was evaluated at 11 and 26 DAS, based on the variables number of leaves, plant height and stem diameter.
The same sesame genotypes were subjected to salinity treatments (0.6, 1.6, 2.6, 3.6 and 4.6 dS m−1), but irrigation with saline water started at 29 DAS, extending until the end of the cycle in order to evaluate plant production. The experiment was set in a randomized block design, with four replicates and four plants in each plot.
Plants were cultivated in 20-L recipients with drains at the bottom to collect and monitor the volumes of drained water. The pots were filled with one layer of crushed stone (2 kg) and another of washed sand (1 kg), covering the bottom. Then, 25 kg of material from a non-saline, non-sodic soil of sandy loam texture that had been previously sieved and fertilized was added. Also, 600 g of organic matter (earthworm humus) was added in order to improve the structure and the water retention of the soil material.
Basal fertilization with NPK was performed by incorporating 100, 300 and 150 mg of N, P2O5 and K2O per kg of soil, respectively, using ammonium sulfate, single superphosphate and potassium chloride.
Irrigations with non-saline water were performed on alternate days until the application of the saline treatments, which started at 29 DAS. Then, plants were irrigated daily with saline water of ECw levels that corresponded to the treatments. Throughout the cycle, soil water content was kept above 80% of field capacity, and a leaching fraction of 20% was applied every 15 days, according to Equation (1).
Top-dressing fertilization was performed via irrigation water, using 50 kg∙ha−1 of N (3 g of ammonium sulfate per pot), divided into two applications (at 34 and 54 DAS) and 20 kg∙ha−1 of K2O (0.41 g of potassium chloride per pot) at 54 DAS. Foliar fertilization was performed at 54 DAS using a liquid nutritional formulation diluted in water at 1%, which contained the micronutrients B (0.5%), Cu (0.2%), Fe (0.10%), Mn (0.50%), Mo (0.10%) and Zn (1.0%).
Growth parameters (number of leaves, plant height and stem diameter) were measured at 29 and 84 DAS.
For the evaluation of sesame production, the number of capsules per plant (NCP) and the mass of seeds per plant (MSP) were recorded. Capsules were collected during the typical maturation phase of each genotype and the drying process was completed in the same greenhouse where plants were cultivated, avoiding losses by dehiscence. Seeds were manually removed from the capsules and weighed using precision scales. The humidity was corrected to 10% in accordance with the criteria used for sesame seed analysis.
The genotypes were classified according to salinity tolerance for each level of ECw tested. The criterion of relative yield was used, which is based on the relative reduction of seed production (g per plant) seen in the treatments (1.6, 2.6, 3.6 and 4.6 dS m−1) in relation to the production obtained using low-sa- linity water (0.6 dS m−1). To classify the genotypes, the following indices of relative reduction of production were adopted, which were adapted from the procedures described in Veatch et al. [
The third experiment also encompassed the entire cycle of the three genotypes, which were cultivated in the same type of recipient described previously. Three irrigation managements were studied. The same saline stress method was used but plant phenological stage varied, following the installation procedures described in the experiment above.
Until 10 DAS, low-salinity water (ECw = 0.6 dS m−1) was given to all plots. Irrigation managements started, also on alternate days, at varying plant phenological stages: WS―plants without saline stress, irrigated with low-salinity water (0.6 dS m−1) during the entire cycle; SS1―plants under saline stress during the vegetative stage (irrigation with water of ECw = 3.6 dS m−1 from 11 DAS to flowering); SS2―plants under saline stress in the reproductive stage (irrigation with water of ECw = 3.6 dS m−1 from flowering to the cycle end). In the other stages, good quality water was used.
Combining all the factors, there were 9 treatments (3 genotypes × 3 irrigation managements) set in a randomized block design with four replications and six evaluated plants per plot.
Growth variables (number of leaves, plant height and stem diameter) were measured at 11 and 79 DAS. The number of capsules per plant (NCP) and the mass of seeds per plant (MSP) were obtained in accordance with the procedures adopted in the previous experiment. Furthermore, in each phenological stage the salinity tolerances of the genotypes were classified based on the production loss of plants under no saline stress.
The data from the three experiments were subjected to ANOVA (F test); means of qualitative variables were compared using Tukey’s test (p < 0.05, and p < 0.01) and means of quantitative variables were subjected to polynomial regression analysis [
Based on ANOVA results, the percentage of germination of the genotypes was not affected by the factors in studies (salt concentrations and genotypes), in isolated action nor in interaction, with mean values of 97.28% for BRS Seda, 92.84% for LAG-927561 (Branquinha) and 96.54% for LAG-26514 (Pretinha) (
In the literature, the effects of salinity on sesame seedling germination are controversial: some studies indicate that this is the stage of highest tolerance, but other studies found differences in sensitivity to saline stress between genotypes [
In addition, the germination speed index (GSI) was not harmed by irrigation water salinity, with a mean value of 19.84 plants day−1 for the salinity levels. However, the three genotypes differed significantly regarding GSI, an important seed vigor index, with the highest value (23.17 plants day−1) found for BRS Seda, followed by LAG-26514 (20.31 plants day−1) and LAG-927561 (16.57 plants day−1) (
AZEVEDO et al. [
Genotypes | GP (%) | GSI |
---|---|---|
Mean | Mean | |
BRS Seda | 97.2839 a | 23.1677 a |
LAG-927561 | 92.8395 a | 16.5688 c |
LAG-26514 | 96.5432 a | 20.3088 b |
Salinity (dS m−1) | ||
0.6 | 96.2963 | 20.1407 |
1.6 | 95.4732 | 20.0944 |
2.6 | 94.2386 | 20.0463 |
3.6 | 96.7078 | 19.9703 |
4.6 | 95.0617 | 18.9240 |
CV (%) | 5.84 | 7.95 |
Means followed by the same letter in the column did not differ for Tukey’s test (p < 0.05); CV = Coefficient of variation.
sources of small farms in Brazil’s semi-arid region [
Salinity significantly influenced plant growth variables but had no effect on the genotypes, either separately or in interaction with the ECw levels. Plant height (
In general, the use of saline water caused a decrease and delay in the initial growth of sesame plants in this study, which corroborates the results observed by Azevedo et al. [
growth of sesame genotypes.
Contrary to the results of this study, in which salinity did not influence the germination and initial growth of the three genotypes, Abbasdokht et al. [
By the analysis of variance of the data of this experiment, covering the entire plant cycle, the effect of salinity depended on the genotype, because for most variables the interaction was significant for these both factors, except for the number of leaves. According to the growth functions (
A small influence of salinity on plant height (
Plant height decreased by 3.08% for BRS Seda, 3.09% for LAG-927561 and 3.91% for LAG-26514 (
Sesame stem diameter (
927561 (mean value of 10.38 mm) and LAG-26514 (8.22 mm), stem diameter was not compromised by the ECw levels of the irrigation water. For these two genotypes, plant height was affected more by saline stress, but there was no reduction in stem diameter, thus compensating for the effects on plant growth.
The number of leaves was not influenced by salinity levels in this study as a mean value of 21.56 leaves per plant (
However, there were differences in leaf emergence between genotypes, with LAG-26514 (Pretinha) being superior (mean value of 27.76 for leaves―
Sesame production components were also affected by the increase in water salinity, which varied with genotype.
The number of capsules per plant (NCP) ranged from 20.06 to 34.56 for BRS Seda, 18.76 to 36.23 for LAG-927561 and from 39.78 to 45.62 for LAG-26514; this latter was the genotype with the highest production, even in the treatment of 4.6 dS m−1, the highest salinity level (
For the highest salinity levels, abscission of flowers and capsules were observed, especially in the strain LAG-927561, but this also occurred in the other genotypes. The abscission of these reproductive structures was probably caused
by the abscisic acid, because the correlation between ABA synthesis in plants under saline stress and the fall of flowers and fruits is present in the literature [
The mass of seeds per plant (MSP―
Considering as a reference the use of 1.6 dS m−1 water for the irrigation of the three sesame genotypes, which is common in the semi-arid region in Northeast Brazil, the production would be 5.46, 5.17 and 6.40 g plant−1 for BRS Seda, LAG-927561 and LAG-26514, respectively. The highest individual production of capsules (number) and seeds (weight) of the strain LAG-26514, even with lower plant growth in height (
Although plants were cultivated in recipients that had limited soil volume (20 L), the estimated productions per unit of area when irrigating plants with 1.6 dS m−1 water would be approximately 726, 687 and 851 kg∙ha−1 for the genotypes BRS Seda, LAG-927561 and LAG-26514, respectively, considering a plant density of 133,000 plants ha−1 (spacing used by family farmers: 1.20 × 0.30 × 0.10 m). Compared with the mass of grains obtained by Aghajari et al. [
in this study is high, considering that these authors obtained 710.9 kg∙ha−1 with a local variety (spacing of 0.50 × 0.10 m?200,000 plants ha−1) when irrigated with water of 2 dS m−1.
The weight of seeds per plant was more affected by salinity than the number of capsules per plant, contrary to the results observed by Aghajari et al. [
In the classification of the genotypes with respect to salinity tolerance, according to the criterion of relative yield based on Veatch et al. [
In a study developed in Iran with two sesame cultivars, Aghajari et al. [
In this experiment, in which salinity effects were evaluated at varying plant phenological stages, the interaction between factors was significant, that is, growth and production components varied according to the stage at which sesame genotypes were subjected to saline stress. This is expected for sesame [
Genotypes | RR (%) | Reduction range | Classification | RR (%) | Reduction range | Classification |
---|---|---|---|---|---|---|
................ ECw 1.6 dS m−1............... | ............ECw 2.6 dS m−1............... | |||||
BRS Seda | 21.42 | 21 - 40 | MT | 42.85 | 41 - 60 | MS |
LAG-927561 (Branquinha) | 16.01 | < 20 | T | 32.06 | 21 - 40 | MT |
LAG-26514 (Pretinha) | 18.49 | < 20 | T | 36.99 | 21 - 40 | MT |
................ ECw 3.6 dS m−1............... | ................ ECw 4.6 dS m−1............... | |||||
BRS Seda | 64.28 | > 60 | S | 85.71 | > 60 | S |
LAG-927561 (Branquinha) | 48.05 | 41 - 60 | MS | 64.07 | > 60 | S |
LAG-26514 (Pretinha) | 55.49 | 41 - 60 | MS | 73.99 | > 60 | S |
T = tolerant; MT = moderately tolerant; MS = moderately sensitive; S = sensitive.
ment stages.
In general, plant growth for the three genotypes was more affected by salinity when plants were irrigated with saline water in the vegetative stage (SS1) compared with the flowering/fruiting stage (SS2) (
In fact, for growth variables, the number of leaves was the most affected by salinity, differing when the three genotypes were irrigated with saline water in the
vegetative stage. Thus, it is the most adequate variable to evaluate tolerance to saline stress. Considering the three genotypes, the strain LAG-927561 (Branquinha) is the most sensitive to saline stress during leaf emergence.
Plants from the strain LAG-26514 (Pretinha) tend to grow less in height and diameter compared with the other genotypes, but present a higher number of leaves, which was also observed in the previous experiment largely due to its branched growth (
Only one study was found on the application of saline stress in different stages of sesame growth [
As for production, no difference was observed between the genotypes for the number of capsules per plant and mean weight of seeds per plant, considering the data obtained in each salinity management (
Comparing these production data (varying phenological stages) with those of the second experiment, in which plants were irrigated with saline water from 29 DAS until the end of the cycle, the productions of capsules and seeds were more affected. That is, the effects of salinity were less harmful to plant production when irrigated with saline water (3.6 dS m−1) starting at 29 DAS, even with the continuation until the end of the cycle. In this condition, saline stress was imposed at the end of the vegetative stage, precisely the stage of highest sensitivity to this stress, according to the results obtained in the third experiment, resulting in less damage to plants.
Similar studies with sesame or other species involving variations in more than one plant cultivation cycle were not found in the literature. For the variation of only the phenological stages in which plants were subjected to irrigation with saline water, there are studies on rice [
differences in the tolerance to saline stress.
For sunflower, also varying the stages in which plants were irrigated with saline water, Morais et al. [
- Irrigation water salinity does not interfere with germination and emergence speed of the three sesame genotypes, but affects seedling growth regardless of genotype.
- The number of leaves is the most adequate growth variable to evaluate sesame tolerance to salinity.
- Plant growth of the genotypes BRS Seda, LAG-927561 (Branquinha) and LAG-26514 (Pretinha) was more affected when saline stress was applied in the vegetative stage, compared with the flowering/fruiting stage.
- Sesame grain production is the most inhibited production component when saline stress is applied in both vegetative and production stages. The strains LAG-927561 and LAG-26514 are promising for studies on adaptation to saline stress.
Suassuna, J.F., Fer- nandes, P.D., Brito, M.E.B., Arriel, N.H.C., de Melo, A.S. and Fernandes, J.D. (2017) Tolerance to Salinity of Sesame Genotypes in Different Phenological Stages. American Journal of Plant Sciences, 8, 1904-1920. https://doi.org/10.4236/ajps.2017.88129