The objective of the research was to evaluate the effects of saline stress on the initial growth and physiological parameters of three varieties of cotton plants, being two cultivars of colored fiber (BRS Topázio and BRS Verde) and one of white fiber (BRS 286). The experiment was conducted under greenhouse conditions. After chemical depletion with sulfuric acid, five seeds were seeded in polyethylene pots of 20 kg, leaving only one plant per pot after thinning. The experimental design was completely randomized, with a factorial scheme of 3 × 5, with five replications, totaling 75 plots, being three cotton varieties and five saline stress treatments—1.1; 3.1; 5.1; 7.1; 9.1 dS m −1. The evaluations occurred at 15 and 30 days after the beginning of the treatments (DAT) for growth variables (plant height, stem diameter, number of leaves and leaf area) and gas exchange (stomatal conductance, net photosynthesis rate and transpiration. The variety that was most resistant to the salt stress levels studied was BRS 286, followed by BRS Topazio and BRS Verde.
Salinity caused by the excessive concentration of salts in the soil solution, or even in the waters used for irrigation, is also considered an abiotic stress limiting the growth and production of plants [
Saline stress causes several physiological changes in the plant, such as reduction of leaf water potential, stomatal closure, reduction of photosynthetic rate, decrease of aerial part, acceleration of senescence, leaf abscission, among others [
The reduction of water absorption by plants, due to excess salts in the soil solution, is one of the main factors that undermine the photosynthetic process. According to [
The cotton crop is characterized as raw material of the agrotêxtil chain, being incorporated in about 90% of the total natural fibers consumed in Brazil. It is domesticated and cultivated in places where water deficiency is not necessarily an aggravating factor [
Due to resistance to low rainfall and moderate levels of salinity, colored cotton has great importance in the semi-arid region. In addition, it is a crop used in the production of textiles due to the non-use of dyes or other chemical derivatives, thus adding more value to the finished product [
Therefore, this research had as objective to evaluate the initial growth, chlorophyll and the variables of gas exchange of different cotton cultivars, when submitted to saline stress.
The research was carried out in a greenhouse, located at the Federal University of Campina Grande-PB, campus I, under the following geographic coordinates: 7˚13'11"S and 35˚52'31"W; altitude of 550 m. The duration of the survey was two consecutive months (September and October 2016). Cotton cultivars were evaluated, being one of white fiber (BRS 286) and two of colored fiber (BRS topaz and BRS Verde).
Before sowing, the seeds were chemically demarcated using sulfuric acid in the proportion of 7 kg of seeds per liter of acid. After delignification, these seeds were washed with 5% sodium hydroxide (NaOH) and water for the removal of linter and sulfuric acid residues. This process is necessary to prevent proliferation of fungi or other agents that may cause seed damage and subsequent germination.
For the distribution of the vessels in the experimental area, a completely randomized design was used, with a factorial scheme 3 × 5, with 5 replications, totaling 75 experimental plots. This factorial scheme is defined by three cotton cultivars (BRS Topázio, BRS Verde and BRS 286) and five different levels of electrical conductivity of water―1.1; 3.1; 5.1; 7.1; 9.1 dS m−1.
Vessels with capacity of two liters were used, containing three holes in the base to allow drainage, and filled with 300 g of gravel to cover, subsequently, filled with 3.5 kg of soil, classified as Argiloso Franco Latosol.
Only foundation fertilization was carried out, incorporating in each vessel amounts of 0.77 g of urea, 5.83 g of single superphosphate and 0.90 g of potassium chloride, according to [
The water in use was stored in reservoirs of 100 L. The different levels of salinity in water (CEa) were obtained from the dissolution of sodium chloride in rainwater and water supply. These concentrations of NaCl, to be diluted to determine the desired CEa, were found based on the equation of [
Conc . NaCl = 585 × ( C E d − C E u ) × V t 1000 (1)
where: Conc.NaCl―Concentration of sodium chloride (g);
CEd―desired electrical conductivity (dS m−1);
CEu―electrical conductivity of used water (dS m−1);
Vt―Total reservoir volume (L).
Five cotton seeds were sown per experimental plot, filled with soil at a depth of 5 cm. The emergence started 4 days after sowing (DAS), thinning at 10 DAS, leaving only one plant per pot. Soil scarification of the soil occurred before each irrigation and mentoring of some plants, in order to avoid tipping. In addition, there were applications of insecticides and fungicides when necessary.
Up to 10 DAS, irrigation was performed with moisture close to the field capacity, using only water supply. From then on, the irrigation occurred from two days in two days, always at 7 o’clock, applying in each vessel the appropriate treatment.
The evaluations occurred at 15 and 30 days after application of the treatments (DAT). The growth of the cotton cultivars was evaluated through the determination of plant height (AP), stem diameter (DC), number of leaves (NF) and leaf area (FA). The leaf area was determined by the equation proposed by [
Y = 0.4322 X 2.3002 (2)
where: Y = Leaf area, cm2; X = Length of main vein of the leaf, cm.
The gas exchange variables of the plants, involving the stomatal conductance (gs) (mol m−2・s−1), net photosynthesis rate (A) (μmol m−2・s−1) and transpiration (E) (mmol m−2・s−1) were measured using the IRGA equipment, brand ADC, model LCpro-SD. These evaluations were carried out between 8 and 10 am, at 15 and 30 DAT. A source of artificial light was coupled to the apparatus in order to obtain a flux density of photosynthetic photons of 1200 μmol m−2・s−1.
At the end of the experiment, 45 DAS, the plants were removed from the vases, separating leaves, stem and root. After weighing the fresh mass of these materials, they were placed in a forced circulation oven at 65˚C for 48 hours. After this period, there was a new weighing to obtain the dry mass of the different parts.
The results obtained from the evaluated variables were submitted to analysis of variance through the statistical software SISVAR. The means were compared by the Tukey test at 5% probability. In the cases of significance, regression analysis was performed [
As observed in
The average results for AP, DC, NF and AF, in the two evaluated periods, were adjusted to the linear regression model (
At 15 DAT, the mean data of AP, DC, NF and AF decreased between the lowest (1.1 dS m−1) and the highest (9.1 dS m−1) saline level of 28.0%, 17.1%, 30.9% and 68.7%, respectively, resulting in a reduction of 3.5%, 2.1%, 3.9% and 8.6%, respectively. At 30 DAT, the linear trend of the mean results continued to decrease, but more sharply, being 39.3% for AP; 27.3% for DC; 57.5% for NF and 73.0% for AF, with a decrease, by unit increase of CEa, sequentially, of 4.9%, 3.4%, 7.2% and 9.1%.
According to [
VariationFactor | GL | ANOVA-SALINE STRESS | |||||||
---|---|---|---|---|---|---|---|---|---|
AP-15 cm | AP-30 cm | DC-15 mm | DC-30 mm | NF-15 | NF-30 | AF-15 cm2 | AF-30 cm2 | ||
Sal. (S) | 4 | 0.0000* | 0.0000* | 0.0000* | 0.0000* | 0.0000* | 0.0000* | 0.0000* | 0.0000* |
Gen.(G) | 2 | 0.0000* | 0.0053* | 0.0661ns | 0.1308ns | 0.0000* | 0.0000* | 0.0000* | 0.0000* |
S x G | 8 | 0.0327* | 0.8229ns | 0.6981ns | 0.1478ns | 0.0017* | 0.0281* | 0.0081* | 0.0049* |
CV (%) | 9.80 | 8.06 | 7.40 | 5.10 | 11.87 | 12.70 | 20.85 | 18.39 |
ns: not significant; *p < 5% by the Tukey test.
number of leaves can show a physiological mechanism of adaptation of the plants to the saline stress, to avoid the loss of water by transpiration [
Similar results were obtained by [
According to
The BRS Verde obtained mean data significantly different from the others, in all growth variables, obtaining the lowest values. [
Regarding the variables of fresh and dry mass (
VariationFactor | GL | ANOVA-SALINE STRESS | |||||
---|---|---|---|---|---|---|---|
MFF | MSF | MFC | MSC | MFR | MSR | ||
g | |||||||
Sal. (S) | 4 | 0.0000* | 0.0000* | 0.0000* | 0.0000* | 0.0000* | 0.0000* |
Gen. (G) | 2 | 0.0000* | 0.0000* | 0.5499ns | 0.0000* | 0.0001* | 0.0009* |
S x G | 8 | 0.0000* | 0.0062* | 0.0734ns | 0.0025* | 0.0090* | 0.0043* |
CV (%) | 13.13 | 11.58 | 10.20 | 12.83 | 4.64 | 15.33 |
ns: not significant; *p < 5% by the Tukey test.
there was a significant effect of the isolated factor S for all these variables. The G factor and interaction (S x G) did not exert significance only in the fresh stem mass variable (MFC).
According to
9.1 dS m−1. This is probably due to the difficulty that plants have to absorb water in environments with low osmotic potential, which leads to less accumulation of mass.
This decrease of fresh and dry biomass of the different parts of the plant may also be related to the reduction of the leaf area, because for [
It is observed in
In relation to the gas exchange variables evaluated (
The G factor, on the other hand, only presented significance at 30 DAT, only in the mean data of stomatal conductance (gs) and transpiration (E). The
Variation Factor | GL | ANOVA-SALINE STRESS | |||||
---|---|---|---|---|---|---|---|
gs-15 | gs-30 | A-15 | A-30 | E-15 | E-30 | ||
Sal. (S) | 4 | 0.8962ns | 0.0104* | 0.0000* | 0.0000* | 0.0000* | 0.0076* |
Gen. (G) | 2 | 0.7196ns | 0.0039* | 0.3906ns | 0.3843ns | 0.1070ns | 0.0045* |
S x G | 8 | 0.1547ns | 0.3354ns | 0.1217ns | 0.5951ns | 0.7011ns | 0.7157ns |
CV (%) | 30.23 | 32.39 | 7.41 | 11.29 | 10.66 | 23.36 |
ns: not significant; *p < 5% by the Tukey test.
interaction (S × G) did not present a significant effect on the gas exchange variables studied.
At 30 DAT, the stomatal conductance (gs) of the cotton cultivars presented a linear decrease, with the increase of saline levels (
This stomatal closure, due to the application of more salinized water, may be related to the osmotic effect associated with the accumulation of salts in the soil solution, besides the reduction of the hydraulic conductivity of the root system, in accordance with the increase of the suberization and lignification of the tissues of the roots of plants submitted to salinity [
In IRGA readings at 30 DAT, the mean values obtained by the BRS Verde variety differed statistically from those found for BRS 286 and BRS Topázio, showing higher average gs results.BRS 286 and Topázio did not differ statistically among genotypes, however, BRS Topázio obtained average results of gs slightly higher than those of BRS 286 (
The variables A and E had decreasing average results, with the increase of salinity in the substrate, at 15 and 30 DAT, according to the linear regression equation (
The liquid photosynthesis rate (A) and transpiration (E) decreased by a unit increase of CEa at 15 and 30 DAT, respectively, of 4.2% and 3.9%, and 7.1% and 5.9 %. Behaviors also found by [
With the reduction of stomatal conductance, other subsequent processes may be impaired, among them, the decline of liquid photosynthesis, due to the decrease of CO2 partial pressure, in the intercellular spaces or in the substamatic
chamber [
According to [
Increasing CEa levels affected significantly the initial growth and gas exchange of cotton cultivars, both at 15 and 30 DAT.
In general, the white cotton cultivar, BRS 286, showed to be more resistant to the levels of salts analyzed, among the cultivars studied. Among the varieties of colored cotton, BRS Topázio proved to be more resistant to saline stresses, obtaining, in some cases, results similar to cultivar white fiber. BRS Verde was the most sensitive among all evaluated varieties.
The authors declare no conflicts of interest regarding the publication of this paper.
Oliveira, H., do Nascimento, R., Silva, S., Cardoso, J.A.F., Guimarães, R.F.B. and Nascimento, E.C.S. (2018) Initial Growth and Gas Exchanges of Plants of Colored Cotton Submitted to Saline Stress. Agricultural Sciences, 9, 1652-1663. https://doi.org/10.4236/as.2018.912115