The experiment was carried out from August to September 2014 in a protected environment (green house), at the Center of Science and Agrifood Technology (CCTA) of the Federal University of Campina Grande (UFCG) located in the municipality of Pombal-PB, Brazil (6º47’20’’ S; 37º48’01’’ W; 194 m).

The experiment was set in a completely randomized design, in a 2 × 5 factorial scheme, which corresponded to two eggplant cultivars (C₁ - ‘Comprida Roxa’ and C₂ - ‘Preta Comprida/Enbu’) and five levels of irrigation water salinity (0.6, 1.2, 1.8, 2.4 and 3.0 dS m^-1), with four replicates and five plants per replicate.

Eggplant plants were cultivated on trays with 30 cells, with the capacity for 0.1 dm³ of substrate, until 30 days after sowing (DAS). The substrate used for the production of seedlings was composed of soil (Entisol fluvisol) and commercial substrate, mixed at the proportion of 1:1, and its chemical characterization is presented in Table 1.

For sowing, five tray cells were used in each treatment, so that each cell received two seeds, in a total of 10 seeds per treatment. At the end of plant emergence, thinning was performed, leaving only the most vigorous plant per cell. The seeds of both cultivars were obtained at a commercial house, with 99% of purity and 95% of germination.

Irrigation was daily performed in order to maintain the soil close to its maximum holding capacity, based on the drainage lysimetry method, and the applied water depth was summed to a leaching fraction of 20%. The applied volume (V_a) per container was obtained by the difference between the previously applied volume (V_prev) and the drained volume (d), divided by the number of containers (n), as indicated in Equation 1.

The preparation of irrigation waters corresponding to the respective salinity levels was based on the relationship between EC_w and the concentration of salts (10 * meq L^-1 = 1 dS m^-1 of EC_w), according to Rhoades et al. (1992), valid for EC_w of 0.1 to 5.0 dS m^-1, which encompasses the tested levels. Freshwater from the local supply system (EC_w = 0.3 dS m^-1), whose chemical characteristics are shown in Table 2, was used in the preparation of the other irrigation waters, after mixing with NaCl, according to necessity. The desired level of electrical conductivity was measured using a portable microprocessor-based conductivity meter, with automatic temperature adjustment.

After preparation, the waters corresponding to each salinity level were stored in 30-L plastic containers, which were covered to avoid evaporation, entry of rainwater and contamination with materials that could compromise quality.

During the experiment, plants were monitored with respect to emergence through the daily count of emerged plantlets, that is, with the cotyledons above the soil level, generating a cumulative

Emergence speed (ES) data were best fitted to a linear model and increased as the levels of irrigation water salinity increased; at the highest level (3.0 dS m^-1), there was an increment of 42% in the ES of eggplant plants (Figure 1A). As to emergence percentage (EP), a linear reduction was observed as salinity increased, which was equal to 52.4% (58.3%) when plants were irrigated with EC_w of 3.0 dS m^-1, in comparison to the control (0.5 dS m^-1) (Figure 1B).

Considering that the germination process depends on the absorption of water and energy, through heat, the reduction in the osmotic potential due to the increase in NaCl contents in the soil decreases soil water potential, reducing the energy of the water in the soil and causing the plant to perform osmotic adjustment (Sá et al., 2013). In addition, the increase in the concentration of NaCl ions causes toxicity to plants and may cause damages to the radicle, thus limiting the seed imbibition process and the absorption of water by the plantlet (Munns and Tester, 2008; Voigt et al., 2009; Taiz and Zaiger, 2013). Similar results were observed in other vegetables such as melon (Secco et al., 2010), broccoli (Lopes et al., 2014), beet (Oliveira et al., 2015a) and cabbage (Oliveira et al., 2015b).

For the variables plant height (PH), stem diameter (SD) and number of leaves (NL), there were progressive reductions in the data, which were best fitted to a linear model, with decreases of 76% (1.87 cm) in PH (Figure 1A), 14.1% (1.06 mm) in SD (Figure 2C) and 69.1% (2.17) in NL (Figure 1D) for plants under EC_w of 3.0 dS.m^-1, in comparison to the control (0.6 dS m^-1). The inhibition of growth caused by salinity is due to the osmotic effect, because it promotes physiological drought. Likewise, there may be a toxic effect, resulting from the concentration of ions in the protoplasm. Hence, the reduction in the water potential of the tissues caused by the excess of salts in the soil solution leads to restrictions in elongation and cell division rates, thus reducing plant growth (Munns and Tester, 2008; Queiroz et al., 2013; Taiz and Zaiger, 2013; Sá et al., 2013; Oliveira et al., 2015a).

The factor cultivars influenced the variables shoot dry matter (SDM), root dry matter (RDM) and total dry matter (TDM). For these variables, in the comparison between cultivars, it was observed that the cultivar ‘Preta Comprida/Enbu’ stood out with accumulations of 0.0086, 0.0028 and 0.0114 g for SDM, RDM and RDM, respectively (Figure 3B, D and F). Additionally, for the factor Salinity, according to the regression equations, the linear model indicated decreases in dry matter production with the increment in irrigation water EC, which were equal to 29.7% (0.0074 g) in SDM (Figure 3A), 129.4% (0.0017 g) in RDM (Figure 3C) and 48.3% (0.0091 g) in TDM (Figure 3E), in plants under EC_w of 3.0 dS m^-1, in relation to the control.

Considering that saline water irrigation increases the index of salinization of the soils and the abundant presence of toxic ions in these soils, due to the accumulation of salts, especially Na⁺ salts, there might occur nutritional imbalance, modification in the osmotic potential of the plant and physiological alterations that interfere with the accumulation of photoassimilates and, consequently, with the accumulation of dry matter (Munns and Tester, 2008; Esteves and Suzuki, 2008; Garcia et al., 2012; Sá et al., 2013; Silva et al., 2013; Lima et al., 2015). Similar results have been reported in the literature. Lima et al. (2015), studying the tolerance of the eggplant hybrid ‘Ciça’ to irrigation water salinity, observed that the crop was sensitive to salinity. These authors reached such a conclusion after observing that crop development was already negatively affected at salinity levels above 0.6 dS m^-1. On the other hand, in a study with the same hybrid, Silva et al. (2013) observed significant reduction in dry matter production of eggplant only at salinity levels above 3.3 dS m^-1.

As to the root/shoot ratio (R/S), according to the regression equation, the data were best fitted to a decreasing linear model, and the highest level of irrigation water salinity (3.0 dS m^-1) led to a reduction of 78.3% (0.23) in R/S, compared with the control (Figure 4). For Sá et al. (2013), this response is related to the greater reduction in root growth, compared with the shoots, aiming to reduce the absorption of salts from the environment, especially in environments with higher salinity levels. This fact was confirmed in the present study, considering the drastic reductions observed in RDM accumulation (Figure 3B). Similar results were observed by Oliveira et al. (2015b), evaluating phytomass accumulation of cabbage plants under saline stress.

Regarding the salinity tolerance index (STI), there were reductions in the tolerance of the cultivars as irrigation water salinity increased, reaching approximately 48.1% in plants irrigated with EC_w of 3.0 dS m^-1, in relation to the control (Figure 5A). For the factor Cultivars, it can be noticed that the cultivar ‘Comprida Roxa’ obtained the highest indices of tolerance, equal to 83.99 and 6.87% higher than that of ‘Preta Comprida/Enbu’ (Figure 5B). Although higher phytomass accumulations were observed in the cultivar 'Preta Comprida/Enbu',these plants greater losses in phytomass accumulation as water salinity progressively increased. These reductions were higher than those observed in the cultivar 'Comprida Roxa', which presents itself as more tolerant to salinity.