THE EFFECT OF SALINITY ON GERMINATION, EMERGENCE, SEED YIELD AND BIOMASS OF BLACK CUMIN

Salinity sensitivity of black cumin (Nigella sativa L.) was studied to determine salinity effects on germination, emergence, biological yield, seed yield and plant height. A set of experiments were conducted under completely randomized design in the germinator, greenhouse and field. Seeds of black cumin were grown in a growth chamber irrigated with normal water, electric conductivity (EC) of 0.3 dS m as the control, and treatments amended with NaCl to obtain EC from 3 to 39 dS m. Different EC treatments (3–39 dS m, 3–15 dS m and 3–9 dS m) were applied at different phenological stages of germination, emerging and seed setting, respectively. The effect of salinity on seed germination, germination rate, shoot length, root length, seedling weight, root to shoot ratio and seed vigor was significant at p<0.01. The highest germination rate (94.8%) was observed at the salinity of 3 dS m and no germination was observed at the salinity of 36 dS m. Increase of salinity from 0.3 (control) up to 15 dS m significantly (p<0.01) influenced the rate and percentage of emergence. The highest germination percentage (52.5%) and emergence rate (9.2 seedlings per day) were achieved in the control treatment. Seed yield, biomass and plant height were affected significantly (p<0.05) by different salinity treatments. The essential oil percentage was not significantly affected by salinity stress. With an increase in the salinity level from 0.3 to 9 dS m, the average seed yield and biological yield were decreased from 105.5 to 40.2 g m and from 550.2 to 268.6 g m respectively.


Introduction
Plants are constantly challenged by various abiotic stresses such as salinity, drought, temperature extremes, heavy metal toxicity, high-light intensity, nutrient deficiency, UV-B radiation, ozone, etc. Salinity causes substantial losses in the yield and crop quality as well as adaptation (Hasanuzzaman et al., 2012).Water, salinity and nutrient are crop growth-limiting factors but weeds, pests and diseases can decrease the potential of crop yield and they are considered as crop growth reducing factors (Dogliotti et al., 2004;Mehta et al., 2012).Salinity is one of chronic and acute plant stress factors in arid and semiarid regions.The severity of salinity problem is related to environmental constraints.It decreases average yields of major crops by more than 70% and causes a rapid change in the social and economic environment, and together with the deterioration of the natural resource base threatens sustainability of farm systems in these regions.A new strategy for the sustainable production is to use marginal lands and saline water sources safely to supplement all post-sowing irrigations and to lead to a substantial increase in production and water resources conservation by declining groundwater and river flow consumption in agriculture systems (Bone et al., 2012).Reducing the salt content of soil and the number of other suitable plants that can tolerate salt is proposed as a solution to the exploitation of these lands (Lokhande and Suprasanna, 2012).Today, planting salt tolerant species, particularly N2-fixing species, is the most useful approach to rehabilitating salt-affected degraded lands (Soliman et al., 2012;Radić et al., 2007).Nigella sativa belongs to the buttercup family or Ranunculaceae, which is a large family.Globally, it consists of around 1,800 species in about 50 genera.Nigella has 8 herbaceous annual or perennial species in Iran (Mozaffarian, 1992).The genus Nigella represents some 14 species of dicotyledonous flowering plants of Mediterranean and West Asian origin, including some species of commercial importance, for example spices, aromatic, medicinal, and ornamental plants in the world (Landa et al., 2006).The main extracted unsaturated fatty acid of Nigella seed is linoleic acid (52.6%), followed by oleic acid (23.5%), while the main saturated fatty acid is palmitic acid (16%).Triacylglycerols and neutral lipids are found to be the most abounded components recorded to 78.4 and 93.2%.The seed oils, therefore, have the potential for use as domestic and industrial oils and contain considerable amounts of protein (20%) and a high amount of lipid (37%).The seeds are shown to be rich sources of potassium, calcium and sodium and other elements (Ali et al., 2012).Nigella seed extract is recognized for traditional healing and as food additive in many cultures with no reported harmful effect (Hamid, 2012).An investigation was aimed at evaluating the impacts of salinity stress on developmental stages, biological yield and seed yield of Nigella sativa.

Material and Methods
Nigella sativa seeds were collected from Semirom region in Isfahan province, Iran.Germination tests were carried out in the laboratory under a completely randomized design with four replications.Salinity treatments were prepared with EC 0.3 dS m -1 (control) and with 3 dS m -1 intervals of using 3 ml of NaCl until high concentrations of salt prevent seeds from germinating.Four samples for each treatment of 100 seeds were placed on a filter paper in Petri dish No. 10, and the seed was treated with Vitavax fungicide.The germinator was adjusted with alternating temperatures of 15/20°C darkness/light, 8/16 hrs at 75% relative humidity.First, they were irrigated with the saline water and then with distilled water.Seedlings were counted after 5 to 10 days from the emergence of the majority of seedlings.Days of germination were calculated based on the emergence of root when its root length was about 2-3 mm (Lin and Xing, 2007).The rate of germination was calculated using the formula (RG)=N 1 /D 1 +N i /D i , where N is a daily increase in seedling number.
Shoot length, root length and seedling weight were measured and seedling vigor was calculated using seedling length × seedling weight (López-Castañeda et al., 1996).The raw numbers (percentages) were analyzed after angular transformation was applied to them.A set of emergence experiments was conducted in 30 cm row spacing under a completely randomized design with four replications and irrigated with salinity water including EC 0.3, 3, 6, 9, 12 and 15 dS m -1 at the farm.The number of emergence seeds was counted per day, which determined the final emergence percentage.Salinity treatments were applied after thinning in the 6-8 leaf stages to reach an equal density in all plots.Weed control was done manually and no herbicides and fertilizer treatments were applied during the growing season.The irrigation was carried out by measuring soil moisture with TDR instrument.Wet and dry biological yield, seed yield per unit area, and plant height were measured after harvesting.
To establish the extraction process of essential oil of Nigella seed, 50 g of seeds after grinding were used for each measurement by applying Clevenger apparatus.Gas chromatography (GC) was used to identify the essential oil compounds.
Statistical analysis of data was performed with the SAS and MSTAT-C softwares.Duncan's multiple range test was used for multiple comparison procedures.

Results and Discussion
Based on the results of this study, salinity has a significant (p<1%) influence on germination, emergence rate, shoot length, root length, seedling weight, root to shoot ratio and seedling vigor (Table 1).The highest germination (94.8%) was observed in the salinity of 3 dS m -1 and the lowest germination (0.0%) in the salinity treatment of 36 dS m -1 , respectively.There was no significant difference (p<0.05) for the average seed germination between the control and the salinity up to 15 dS m -1 (Table 2).Emergence rate was different from 17.9 seeds per day for the of 6 dS m -1 to 0.0 seeds for the salinity of 33 and 36 dS m -1 .The maximum seedling length of 2 cm and the maximum weight of seedling shoot of 0.68 mg were recorded for the salinity of 9 dS m -1 .Moreover, the maximum root length was 3.6 cm for the salinity of 3 dS m -1 .The highest seed vigor was 0.6 for the salinity of 9 dS m -1 .The lowest rates for all the measured characters were observed for the salinity of 27 dS m -1 .Root/shoot ratio for seedling length was decreased from 2.3 to 1.2 by increasing the salt concentration from the control to 24 dS m.However, the other study reported a decrease in root length and shoot length of N. sativa seedling by increasing salinity to 150 ml mol at a constant temperature of 25°C, with a germination rate of 95 to 82% in less than a week (Hajar et al., 1996).
The effect of salinity on seedling emergence and seedling survival of Nigella sativa was studied in the field.According to the results, the salinity treatment significantly decreased (p<0.01) the seedling emergence percentage (52.5%)and emergence rate (9.2 seedling/day) from the control up to 15 ds m -1 where no seedling emergence was observed.High NaCl concentrations caused a significant (p<0.01)reduction in biological yield and seed yield (Table 3).Results indicated that the increased salinity from 0 to 9 dS m -1 caused a significant (p<0.05)reduction from 54.8 to 42.1 cm in plant height, from 105.5 to 40.2 g m -2 in seed yield and from 550.2 to 268.6 g m -2 in biological yield (Table 4).These changes were associated with an increase in the relative water content and the Na+ concentrations (Nia et al., 2012).Saline soil causes physiological and metabolic disturbances in seed germination, survival percentage, morphological characteristics of plants, affecting development, growth, yield, and quality of plants (Al-Jassir, 1992;Rameeh et al., 2012).

Table 1 .
Analysis of variance (ANOVA) of seed germination, seed characters, germination and seedling growth in salinity treatments.

Table 2 .
Means of black seed germination traits in different salinity treatments.

Table 3 .
Analysis of variance for the agronomic traits of Nigella sativa grown in different salinity treatments.
* and ** represent a significant difference at p<0.05 and p<0.01, respectively.

Table 4 .
Comparison of the effects of different salinity levels on agronomic characters of Nigella sativa.

Table 5 .
Chemical composition of Nigella sativa essential oil in regard to different soil salinities.Salinity sensitivity of black cumin varied in different growth stages from germination to seed setting.The changes of chemical composition of Nigella sativa essential oil were not influenced by different soil salinities.It can be concluded that with an increase in salinity levels there was a significant reduction in biomass and seed yield in black seeds without any particular trends of changes in essential oil.