Evaluation of wheat varieties to salt stress ( NaCl ) for seed germination and early seedling growth under laboratory conditions

Salinity tolerance during germination and early seedling growth was evaluated of four wheat varieties under four salinity (NaCl) levels that included Control (distilled water) 0, 9, 12 and 16 dSm. The seeds of four wheat varieties including Imdad-2005, Mahran-89, TJ-83 and TD1 were sown under various NaCl levels in Petri dishes. The trial was performed at Seed Testing Laboratory, Department of Agronomy, Sindh Agriculture University, Tandojam Pakistan, following completely randomized design with three replications. The results showed that different salt stress (NaCl) levels had significant effects on germination (%), shoot and root length (cm), shoot and root water content (%), shoot and root fresh weight (g) and shoot and root dry weight (g) of wheat varieties. Among varieties, Imdad-2005 showed tolerance against salt stress for all parameters as compared to other varieties. The Imdad-2005 produced maximum mean germination (93.7%), shoot and root length (14.8 cm and 9.3 cm), shoot and root RWC (80.1 % and 86.2%), shoot and root fresh weight (2.3 g and 1.5 g) and heaviest shoot and root dry weight (0.28 g and 0.13 g). However, for NaCl levels, maximum germination (96.2 %), shoot and root length (15.5 cm, 10.7 cm), shoot and root water content (86.4 %, 87.0%), shoot and root fresh weight (2.3 and 1.5 g) and highest shoot and root dry weight (0.28 g and 0.13 g) was noted at control, where seeds were on sown by using distilled water.


Introduction
Wheat (Triticum avestivum L.) is considered as a major cereal crop and staple food worldwide.Wheat meets the increasing food requirements of the country.Among all cereals, it occupies the significant position and adds 13.1 (%) value-addition in agriculture and 2.8 (%) in GDP.Wheat contains the fundamental nutrients which are needed in our daily diet.United States consumes wheat as stable food more than any country of world [1].Wheat is the highly nutritious.It has contained essential fibers, carbohydrates, protein and vitamins.There are many byproducts of wheat such as flour, bread, pastries, cakes and other local foods [2].Soil salinity is one the main constraints that adversely affect the growth and development of the wheat crop globally.Salinity generally occurs in areas of acute water shortage.Like other countries Pakistan is also greatly facing the issue of soil salinity [3].Yield of crop declines as the pH of the soil solution crosses 8.5 and the EC value increases upto 4 dSm -1 .Increased EC value reduces yield of cultivated crops.Inclusion of salts in water decreases its osmotic potential, which results in the reduced accessibility of water to roots [4].The micro environment of the plant plays a vital role in creation of saline soils which is characterized by low rainfall, great fluctuations in temperature and high rate of evaporation [5,6].Seed germination and seedling growth are known as critical stages to salt stress [7].That might be due to increased toxicity in ions [8,9], reported that some plants are sensitive to salinity at shoot growth stage because the tolerance to salinity in the plant is not yet fully developed.Root and shoot length is one of the dominant factors for salt stress because roots are in direct touch in soil and they uptake the water and minerals from soil and supply it to other parts of the plant.Root and shoots traits are important indicators that greatly determines the response of the plant to salt stress [10,11].Moreover, these parameters provide valuable clues selections of genotypes for future breeding programs [12,13].Assessing genotypic variation under salinity conditions is mandatory in determining the tolerance of crop plants against salt stress [14].This study aimed the assessment of the tolerance of four wheat varieties to salt stress at the germination and early seedling growth stage.

Experimental site
The trial was conducted to determine the tolerance of wheat varieties for seed germination and early seedling growth under various salinity levels during 2013-14 in the Seed Testing Laboratory, Department of Agronomy, Faculty of Crop Production, Sindh Agriculture University Tadojam, Pakistan.

Experimental details
For this study, Hoagland nutrient solution was used as growing medium.The 1/4th strength of the nutrient solution was used.The chemical combination of nutrient solution is presented in (Table 1).The four local wheat varieties were evaluated under various NaCl levels that included 0, 9, 12, and 16 dSm -1 .The seeds were sterilized for ten minutes in 5% sodium hypochlorite and were cleaned with distilled water.Fifteen seeds of each variety were planted on molded plastic sieves placed in plastic bowls at temperature 20-25ºC.The seed germination percentage was recorded after five days.The bowls were covered with porous transparent polyethylene bags to avoid excess evaporation.The bowls were placed in controlled growth chamber maintaining the temperature of 20-25ºC day and night temperature and 12 hours photoperiod irradiate 22 wn2.The photoperiod period of 12 hours was maintained.Topping of each bowl was done regularly to maintain the same level of moisture with the respective concentration of a nutrient solution.

Statistical analysis
The data was obtained and subjected to the analysis of the variance (ANOVA).The least significant difference test was applied to examine the statistical differences within treatments following the method developed by [15].After 5 days, germination percent (%) was measured according to the International Seed Testing Association (ISTA) standard method.At the end of the fifth day, the germination percentage was measured according to the following formulas; Formula.1: GP =

Results and discussion
The results demonstrated that the all parameters at germination and early seedling growth of wheat verities were significantly influenced by salt-stress.Our results agreed with [16].Who observed that increasing levels of salinity had harmful effects on all the parameters.Seed germination (%) Germination (%) suppressed under high saline conditions.The salt stress showed adverse effect on seed germination (Table 2), among different NaCl levels, the maximum germination (96.2%) was recorded under control condition (0 dS m - 1 ), followed by (91.5% and 88.2%) that were noted at 9 and 12dS/m -1 levels respectively.However, minimum germination (85.0%) was recorded at 16 dSm -1 .Our findings are further confirmed by [17] who described that salt stress causes more ionic toxicity that reduces the absorption of water in the seeds that ultimately leads to less germination (%).
[18] also found that a less germination (%) might be due to less osmotic potential to nutrients media.In case of varieties, highest germination (93.7%) was noted in variety Imdad-2005, followed by (91.2% and 89.7%) that was recorded in Mehran-89 and Tj-83 varieties.However, lowest germination (86.2%) was noted in TD-1.Interaction between varieties and NaCl levels showed that maximum germination (98.0%) was recorded in variety Imdad-2005 under control 0dS/m -1 NaCl level.Moreover, the minimum germination (80.0%) was observed in variety TD-1 at 16dS/m -1 level [19], also found different response of wheat varieties under different salinity levels.The findings of [20], endorse the results of the present investigation, who suggested that salt stress conditions showed adverse effects on germination % of wheat cultivars of wheat.Moreover [21], also demonstrated that most of the cultivars of wheat showed less germination under salt stress conditions.

Shoot length (cm)
The results related to shoot length indicated significant (P<0.05)response of wheat cultivars to salt stress.The decreased shoot length was recorded at increasing level of NaCl concentration (Table 3).The maximum shoot length (15.5 cm) was recorded under control condition 0 dS/m -1 NaCl level, followed by (14.8 cm and 13.8 cm) that were noted at 9 dS/m -1 and 12 dS/m -1 , respectively.However, minimum (10.6 cm) shoot length was obtained from 16 dS/m -1 level.These findings are supported by [22], who described that soil salinity adversely affects shoot growth of plants by altering water relations due to salt accumulation in intercellular spaces.In case of varieties, longest shoot length (14.8 cm) was recorded in variety Imdad-2005, followed by (13.9 cm and 13.4 cm) that were noted in Mehran-89 and Tj-83, respectively.Moreover, lowest shoot length (12.8 cm) was obtained from variety TD-1.The interaction between varieties and NaCl levels revealed that the maximum shoot length (16.7 cm) was noted in variety Imdad-2005 under control 0dS/m -1 level.However, minimum shoot length (9.4cm) was observed in variety TJ-83 at 16dS/m -1 NaCl level.Our result are in agreement with [23], who also found that seedling establishment at early growth stages of plants is crucial for getting maximum shoot length and consequently higher yield.The findings of [24], also support the results of current investigation who also observed reduced growth of wheat cultivars under higher level of salt concentrations.

Relative water content of root (%)
The data related to relative water content of root revealed highly significant response of wheat varieties to various salinity levels.
The interaction between varieties and NaCl levels was also significant (Table 6).The maximum relative water content (RWC) of root (86.9%) was recorded under control conditions (0 dS/m -1 ) followed by (84.3 % and 81.3%) that was noted at 9 dS/m -1 and 12 dS/m -1 , respectively.However, the minimum RWC (77.Fresh Shoot weight (g) Shoot fresh weight was affected by the different concentrations of NaCl levels (Table 7), among various NaCl levels, the maximum shoot fresh weight (3.0 g) was recorded under control condition (0 dSm -1 ) ), followed by (1.9 g and 1.7 g) shoot fresh weight that was noted under salt stress conditions of 9 dSm -1 and 12 dSm -1 , respectively.While, minimum shoot fresh weight (1.5 g) was observed under highest salinity level of 16 dSm -1 .In case of varieties, highest shoot fresh weight (2.3 g) was obtained from variety Imdad-2005, followed by (2.1 g and 1.9 g) that was noted in Mehran-89 and Tj-83, respectively.
Moreover, lowest shoot fresh weight (1.7 g) was recorded in TD-1.The results of [32], are also in agreement with the findings of current study, who reported that the shoot fresh weight was induced by salinity stress [33], also observed that the root fresh weight was not affected by salt stress however, shoot fresh weight was significantly affected by salinity.The interaction of varieties and NaCl levels showed that the maximum shoot fresh weight (3.6 g) was recorded in variety Imdad-2005 under control conditions (0dS/m -1 ).However, minimum shoot fresh weight (1.3 g) was noted in variety TD-1 at 16 dSm -1 salt condition.

Root fresh weight (g)
The results related to fresh weight of wheat varieties as influenced by various NaCl levels are given in (Table 8).The result showed that the highest root fresh weight (2.2 g) was recorded in control treatment (0 dSm -1 ), followed by root fresh weight (1.2 g and 1.1 g), observed at salt stress levels of 9 dSm -1 and 12 dSm -1 levels, respectively.While, lowest root fresh weight (1.0 g) was noted at 16 dSm -1 NaCl level [34].Among the wheat varieties, highest root fresh weight (1.5 g) was recorded in variety Imdad-2005, followed by (1.4 g and 1.3 g), observed in Mehran-89 and Tj-83 varieties.The lowest root fresh weight (1.2 g) was noted in TD-1.The interaction between varieties and NaCl levels showed that the maximum root fresh weight (2.7 g) was recorded in variety Imdad-2005 under control (0 dSm -1 ) salinity level.However, minimum root fresh weight (0.9 g) was observed in variety TD-1 at 16 dSm -1 salinity level.

Shoot dry weight (g)
The results showed that shoot dry weight decreased significantly with increasing salinity levels in all varieties.The interaction between varieties and salt stresses was also significant (p>0.5) in (Table 9).The highest shoot dry weight (0.31g) was recorded at 0 dSm -1 level, followed by (0. 25 g and 0.22 g) that were noted at 9 dS m -1 and 12 dSm -1 respectively.While, minimum shoot dry weight (0.19 g) was noted from the highest level of NaCl (16 dSm -1 ).In case of varieties, the highest shoot dry weight (0.28 g) was recorded in Imdad-2005, followed by (0. 25 g and 0.

Root dry weight (g)
Root dry weight showed a significant reduction with increasing salinity levels.In this study, NaCl levels significantly affected on root dry weight of different wheat varieties (Table 10).The maximum root dry weight (0.13 g) was recorded at 0 d Sm -1 level, followed by (0.10 g and 0.8 g), recorded at salt stress levels of 9 dSm -1 and 12 dSm -1 , respectively.While minimum root dry weight (0.
; GP = Germination percentage, NGS = Number of germinated seeds and NTS = Number of total seeds.

Formula. 2
= Relative water content, FW = Fresh weight and DR = Dry weight.