International Journal of Farming and Allied Sciences
Available online at www.ijfas.com
©2014 IJFAS Journal-2014-3-5/502-511/ 31 May, 2014 ISSN 2322-4134 ©2014 IJFAS
Study of Some Phtsiological and Morphological Changes as a Measure of Salt Tolerance in
Different Wheat Genotypes
Kamil M. AL- Jobori
1and Saif edin A. Salim
21. Institute of Genetic Engineering and Biotechnology for Post Graduate Studies-University of Baghdad, Iraq 2. Desert Studies Center- AL-Anbar Univ, Iraq
Corresponding author: Kamil M. AL- Jobori
ABSTRACT: The purpose of this study is to evaluate salt tolerance status of three wheat (Triticum aestivum L.) mutant, M/53, M/4, and M/8, and their origin Saberbeg. Seeds were planted in 12cm diameter pots filled with 7 Kg of coarse washed sand, under field condition with rainfall shelter. Saline water of 0.67( control), 6, 10, and 14 dsm-1 were prepared from diluting natural drainage water(65.5 dsm-
1 ) and used for irrigation. Leaf water potential (LΨw ) , leaf osmotic potential (LΨs) and leaf turgor potential (LΨp) were measured with thermocouple psychrometer. Evapotranspiration (ET) was calculated through growth season, grain yield/ pot, and its component were determined at harvesting.
Mutant M/53 showed more 100 grain weight than its origin and other mutants . Leaf surface area (LSA), weight of roots, straw and yield component were reduced by increasing salinity, this responsible for the reducing in grain yield/pot. Mutant M/53 showed more negative leaf water and osmotic potential, and accumulated more K+ in their roots and leaves. Also showed high (ET) than its origin and other mutants.
Evapotranspiration (ET) tended to decrease as salinity increased, and the same trend showed with (LSA) by decrease in their values as the osmotic potential decrease. The result of this study showed that mutant M/53 more tolerance to saline condition than its origin Saberbeg and other mutants (M/4, and M/8). In conclusion, the results suggested to possible adoption of such physiological and morphological changes(ET, LAS, leaf water and osmotic potentials and K+ accumulation in addition to yield response) as measure of salt tolerance in screening wheat genotypes.
Keywords: Wheat , salinity, tolerance, Plant ecophysiology, Water relations INTRODUCTION
Salinity of soil is contemplated as a major problem which negatively affects a multitude of metabolic processes of plants resulting in reduced growth and yield of most crops (Ahmad, 2011). About one-fifth of irrigated world agricultural lands are adversely affected by salinity, leading to induction of a wide range of perturbations at cellular and whole-plant levels (Belkheiri and Mulas, 2011). Salt stress may provoke (i) osmotic or water-deficit effect which cause reduction of water and nutrient uptake and (ii) ion-excess effect resulting from altered K+/Na+ ratios and/or accumulation of toxic levels of Na+ and Cl¯. Salt stress-induced oxidative stress results from excess reactive oxygen species (ROS) formation (Munns and Tester, 2008) which damages membrane lipids, proteins and nucleic acids (Mittler, 2002).A number of studies on different plant species have shown that K+ uptake is hindered by saline stress which results in decreased K+/Na+ ratio (Lenis, 2011; Kanwal, 2013) which is harmful for plants, because K+ is very important for the maintenance of ionic homeostasis in the cytosol (Szczerba, 2009), and turgor,
503 osmotic adjustment and stomatal regulation (Najafian, 2009; Kusvuran, 2012). The maintenance of high ratio of K+/Na+ in plant tissues can be used as an effective selection criterion for salt tolerance in plants (Reynolds, 2005).
Increasing CL- and Na+ in irrigated water and soil caused decrease in plant absorption of Ca+, Mg+, K+, P+, Fe+, Mn+, Cu+ and Zn+ ions (Uqaili et al, 2002) and reduced yield and its components (Al-Mshhadany, 1985; Farag , 2002) . Salinity has inhibitory effects on wheat phenological aspects such as leaf number, leaf rate expansion , root/shoot ratio , and total dry matter yield (El-Hendawy, 2005; Asgari , 2012). Leaf Na+ and Cl- concentrations of all genotypes increased significantly with increasing soil salinity (Asgari, 2012). Increase of salinity levels decreased seed yield, 1000 –seed weight and K+ concentration, Based on Na+/K+ ratio(Keshavarz, 2013). Studies on the effects of salt stress on different wheat genotypes have shown that sodium and potassium content and their ratio and shoot dry matter are appropriate traits for screening wheat genotypes for salt tolerance (Goodarzi and Pakniat, 2008). It is also reported that genotype ranking in terms of shoot dry weight lead to the same result as grain yield ranking (El-Hendawy, 2011; Sharbatkhari, 2013). Water relation characteristics including osmotic potential, water potential and turgor potential are markedly affected due to saline stress. Reduced solute potential due to saline conditions significantly affects water uptake ability of plants (Munns, 2002) thereby causing water potential more negative which results in reduced growth of most plants (Cha-um, 2010; Eisa, 2012).
Water potential of plants growing under salt stress becomes more negative with an increase in salinity of the rooting medium (Khan, 2001; ) which causes detrimental effects on plant growth. Osmotic stress has the major contribution in salt-induced growth reduction at initial phase of salinity(Siddiqi and Ashraf ,2008). The reduction in osmotic potential in salt stressed plants mainly occurs due to the accumulation of inorganic ions (Na+, Cl- and K+) (Hasegewa, 2000). Osmotic adjustment in all plant tissues contribute to uptake of water uptake and hence maintenance of cell turgor, thereby allowing physiological processes such as stomatal regulation, photosynthesis, and cell expansion (Serraj and Sinclair, 2002). Although a number of physiological and biochemical selection criteria have been recommended for screening germplasm of different crops, water relations are considered very important in view of their direct role in sustaining plant growth under saline stress (Ashraf ,2004). Osmotic potential (Ψs)and turgor potential (Ψp)decreased in tomato and wheat as salinity levels increased . Plant yield for certain were well correlated with leaf water potential (Ψw)and Osmotic potential (Ψs) dedicating that theses measurements may provide a good characterization of salt stress (El-Sharawy, 1997;) Soil salinity is considered an important limiting factor that restricts cultivation of wheat in the middle and southern of Iraq. The best solution to overcome the salinity problem is by improving salt tolerant crops and by devising a screening capable procedure. These include restriction and accumulation of ions, osmoregulation, leaf water content, leaf water potential (LΨw)
, osmotic potential (LΨs), and turgor potential (LΨp), yield and yield components and other parameters ( Al-Mshhadany, 1985; Yildiztugay, 2014 ). In view of this, the present study was conducted to evaluate salt tolerance status of three wheat genotypes and its origin Saberbeg. And to assess whether growth changes, yield and its components and water relation parameters could be used as prospective selection criteria for screening available wheat germplasm for salt tolerance.
MATERIALS AND METHODS
The experiment was conducted in field with rainfall shelter. Seeds of four wheat genotypes (Triticum aestivumL.) (Saberbeg and its mutants M/8, M/53, and M/4) (obtained from plant breeding section, Ministry of Science and Technology) were germinated and vernalized before transplanting to satisfy the cold requirement of these cultivar. Seeds were placed on blotter paper in covered Petri dishes and incubated in dark at 10C for 3 weeks. The seedlings were subsequently transplanted in 12cm plastic pots filled with 7 kg of coarse washed quartz sand. The hydraulic conductivity and field capacity of sand used in this experiment was 0.9575 cm/min and 16.84%, respectively. Saline solutions of 6, 10, 14 dsm-1 were prepared from diluting the natural drainage water of high salinity level established 65.5 dsm-1 and used for irrigation ,plus control (tap water of 0.67 dsm-1). (Table.1) Treatment were arranged in complete block design (RCBD) with three replications. All plants were watered with full-strength nutrient solution, The concentration of the major elements in the nutrient solution were as described by Hoagland and Snyder(1933). Micronutrients were provide according to the recommendation of Johnson, (1957).
The solution contained, in mM/liter: Ca(NO3)2,4H2O,5.0;KNO3,5.0;MgSO4.7H2O,2.0; KH2PO4,1.0; and in mg / liter, 1.77CL as KCL,0.27 B as H3BO3 , 0.27 Mn as MnSO4.H2O, 0.13 Zn as ZnSO4.7H2O,0.03 Cu as CuSO4.5H2O, and 0.01 Mo as (NH4)6Mo7O24.4H2O.The stock iron solution contained 0.6 % FeSO4.7H2O and 0.4 % tartaric acid. One milliliter of the stock iron solution was added to a liter of the nutrient solution to supply 1.21
504 mg / liter Fe. The pots were rearranged randomly every two weeks to minimize possible error by position effects in the shelter.
Measurement of ion uptake
The roots and two leaves below the flag leaf were sampled at heading stage, they were dried at 65-700C and grounded to small pieces. The roots were obtained by using flooding method(AL-Mshhadany,1985).Half gram of the dried leaves and roots was weighted directly in to small beaker. Ten ml of the mixture of digestion acid (4:1 nitric-perchloric acid) was added to each beaker and allowed to predigest over night. The digested material was heated to 125 oC until the volume was reduced to 2ml. The volume was completed to12.5 ml with concentrated HCl, then to 50ml with distilled water (John and Soltanpour, 1980). The ions (Na, K, Ca, Mg, and P) in the leaves and roots in the digests were read on inductively coupled plasma spectrometry (ICP).
Table1.Chemical analysis of drainage and tap water used for irrigation Chemical analysis pH EC
dsm-1
Ca Mg K Na SO4 CL
Meq/L
Tap water 7.26 0.67 2.75 1.70 0.03 1.60 1.20 2.16 Drainage water 7.75 65.5 108.2 318.5 4.2 420.5 44.4 795.2 Measurement of water status:
Leaf water potential (LΨw)
A fully expanded youngest leaf was excised from each plant at 08:00, and the leaf water potential measurements were made by using thermocouple psychrometer (model HR-33-T Logan).
Osmotic potential LΨs
The same leaf as used for water potential measurement was also used for osmotic potential determination.
The leaf material was frozen in 2.0 cm polypropylene tubes for two weeks at -70co and after which time it was thawed, and the sap was extracted by pressing it with a glass rod. The sap so extracted was used directly for osmotic potential determination in an osmometer.
Turgor pressure LΨp
It was calculated as the difference between water potential and osmotic potential values (Nobel, 1991).
Ψp = Ψw – Ψs
Evapotranspiration (ET) : The irrigation water applied was calculated according to eq. (1).
The amount of evapotranspiration was calculated using the water balance method (James, 1988) (eq. 2):
where WPC and W are pot capacity weight (kg) and pot weight (W) just before irrigation, respectively; ET is the amount of evapotranspiration in a pot (L pot-1),
W1 and W2 are the pot weights (kg) just before nth and (n + 1)th irrigation, respectively, I and P are amounts of applied water and rainfall (kg) respectively, and is water bulk density (1 kg L-1). Since the leaching fraction was taken as zero, the amount of drainage was not included in eq. 1.
Agronomic measurements
Leaf area (LA) was determined nondestructively by measuring the length and greatest width of each leaf blade (assuming length×width×0.75)
505 (El-Hendawy, 2009). Straw and roots weight , grain yield and weight of 100 seeds were determined after harvesting.
Metrological data
Air temperature, relative humidity, and global irradiance in the shelter during the experiment are shown in table Table .2 Air temperature (AT), relative humidity (RH) and maximum global radiation (R1) during the study period
Months AT co
RH% RI
MJ m-2 day-1 Max. Min.
Nov. 25.9 13.7 64.8 256.62 Dec. 21.2 7.0 62.1 190.80 Jen. 18.1 6.2 69.2 234.61 Feb. 21.4 7.8 40.4 294.60 Mar. 25.2 0.8 42.2 400.71 Apr. 33.1 6.3 40.3 537.73 May. 40.5 19.9 29.6 571.24
Statistical analysis
Data were analyzed using MSTAT statistical package. Mean comparisons were performed using least significant difference (LSD) test (P< 0.01 and 0.05).
RESULTS AND DISCUSSION
Highly significant differences among salinity concentrations and genotypes (P<0.001 or P<0.01) in ions uptake, water status and agronomic parameters were observed in this study.
Ions Uptake
The sodium , potassium , calcium, magnesium and phosphorus ions content in the leaf sap and roots varied significantly among the genotypes and a significant genotype × salinity interaction showed that the genotypes acted differently in sodium and potassium absorption under salt stress (Table 3).Sodium concentration in leaf sap and root increased significantly with increase in salinity. Among genotypes maximum Na' concentration 83 Mmole kg-1was found in leaf of Saber-beg and 670 in root of M/53 , and minimum 49 Mmole.kg-1 in the leaf of M/53 and 464 Mmole kg-1in root of M/4 at lower salinity level 6 dsm-1 , whereas at higher salinity level 14 dsm-1 , maximum Na' concentration 354 Mmole.kg-1 was found in leaf sap of M/8 and 1307 Mmole kg-1 in M/53 roots ,and minimum 133 Mmole kg-1 in leaf sap of Saber-beg and 985 Mmole kg-1 in roots of M/8 (Table 3).These finding are agreed with the results obtained by (Asgari, 2012 ;Sharbatkhari, 2013).In salt-sensitive genotypes of wheat, sodium was less effectively excluded from the transpiration stream as it entered the leaf blade, so resulting in a higher sodium accumulation (Benderradji, 2011). The sensitivity of some crops to salinity has been attributed to the inability for maintenance of Na+ and Cl-ions out of the transpiration stream (Munns, 2002). Maintenance of adequate levels of K+ is essential for plant survival in saline habitats (Khatun and Flowers, 2005). In saline conditions, high levels of external Na+ could disrupt the integrity of root membranes and alter their selectivity (Reddy, 2003). Salinity disturbed the K+concentration, but its effect was more pronounced at high salinity. Overall, addition of salts decreased the K+ concentration in leaf sap except M/53, whilst in root not affect. On an average, there was a non- significant reduction in K+ concentration of leaf sap at high salinity level. Whilst addition of salts increased the K+
concentration in root significantly. , maximum K+concentration was found in leaf sap and root of M/53 were 489 and 71 Mmole kg-1 , respectively ,whereas minimum 292 and 22 Mmole kg-1 in the leaf and root of M/4 , respectively at high salinity14 dsm-1 (Table 3). mutant M/53 accumulated more K+ in their leaves as salinity increased compared with other genotypes which showed a remarkable inhibition in K accumulation in their leaves as salt concentration increased. Increase of salinity levels decreased K+ concentration (Keshavarz, 2013) .The leaf potassium content has been suggested as a weak index of salt tolerance compared to sodium content under field conditions (El-Hendawy, 2009). In similarity with Na+, mean concentration of Ca also increased significantly with an increase in salinity. Among genotypes, at 6 dsm-1 maximum Ca concentration 178 and 404 Mmole kg-1was found in leaf sap and root of Saber-beg, and minimum in leaf sap of M/4 and the root of M/53 were 109 and 313
506 Mmole kg-1 , respectively, whilst at 14 dsm-1 , M/4 accumulated the maximum Ca in the leaf sap and the root of Saber-beg were 275 and 568 Mmole kg-1
Table .3 elements content in leaves and root of four wheat genotypes Genot types
(G)
EC dsm-
1
Leaf ion content Mmole.kg-1 Root ion content Mmole.kg-1
K Na Ca Mg P K Na Ca Mg P
Saber-beg
0.67 6 10 14 x-
537 492 423 383 459
3 83 121 133 85
120 178 153 155 152
103 96 85 91 73
47 69 85 91 73
25 35 43 44 37
437 642 895 1184
790
303 404 472 568 437
93 186 304 458 206
1 3 48 62 28.5
M/53
0.67 6 10 14 x-
307 489 407 489 423
1 29 51 260 85
96 127 106 182 128
36 51 32 53 43
36 51 32 53 43
18 46 52 71 47
244 670 976 1307
799
322 313 243 380 315
102 255 360 742 365
1.0 1.0 40.67 53.33 24.0
M/4
0.67 6 10 14 x-
312 196 176 292 244
1 7 10 285 198
103 109 143 275 167
36 75 80 64 64
36 75 80 64 64
18 29 29 22 25
242 464 452 1082
560
242 363 301 366 318
129 304 387 492 328
21.0 29.0 31.33 17.5 24.71
M/8
0.67 6 10 14 x-
72 157 188 345 190
1 84 87 354 132
17 137 166 233 177
76 48 35 37 40
76 48 35 37 40
21 26 35 29 28
524 525 1019
985 763
405 319 299 504 382
209 328 471 542 384
1.0 1.0 1.0 1.0 1.0 S
G S X G
R LSD0.05 S LSD0.05 G LSD0.05 S X
G
NS
**
* NS ---- 96.63 193.26
**
NS NS NS 130.57
---
**
NS NS NS 48.71 ---
**
**
NS NS 73.70 73.70 ---
NS
**
NS NS --- 23.73
---
**
**
NS NS 10.09 10.08 ---
**
NS NS 228.39 ---
*
* NS 94.62 94.26 ---
**
NS NS 125.85 ---
*
*
* 2.99 2.99 5.99 --- G =Genotypes; S= salinity ; R = replicate ; * , ** indicate. a significant treatment effect as p=0.05 and 0.01, respectively ; NS =
Not significant.
respectively, while Saber-beg had minimum Ca concentration in leaf sap and in the root of M/4 were 155 and 366 Mmole kg-1, respectively. Maintenance of higher Ca2+/Na+ and K+/Na+ ratios in cv. S-24, Inqlab-91 and G.A- 20 in their roots and leaves compared to the other cultivars could be related to their higher degree ofsalt tolerance(Kanwal, 2013). The highest magnesium content 96 Mmole kg-1 was observed in the leaf of Saber-beg and 387 Mmole kg-1 in roots of M/4 ,and the lowest one 48 Mmole kg-1 observed in the leaf of M/8 and 186 Mmole kg-1 in roots of Saber-beg at lower salinity level 6 dsm-1. Whilst at higher salinity level 14 dsm-1 , maximum Mg' concentration 91 Mmole kg-1 was found in leaf sap of Saber-beg and 748 Mmole kg-1 in roots of M/53 , and minimum in leaf sap of M/8 and roots of Saber-beg were 37 and 458 Mmole kg-1 , respectively. The highest P content of leaf and root belonged to genotypes M/4 were 75 and 29 Mmole kg-1 , and the lowest content were 48 and 1 Mmole kg-1 to M/8 at lower salinity level 6 dsm-1.Whereas at higher salinity level 14 dsm-1 , maximum P' content of leaf and root 91 and 62 Mmole kg-1 ,respectively, belonged to genotypes Saber-beg. In most cases, excess of salts in soil solution leads to a reduction in phosphorus concentration in the tissues of plants, but the results of some studies show that salinity may increase but that does not affect the uptake and accumulation of phosphorus (Kaya, 2001). Kochian (2000) suggests that the reduction of the availability of phosphorus in saline soils is the result of the activity of ions antagonists, which can reduce the activity of phosphate and phosphate transporters of both high and low affinity, which are necessary for the uptake of phosphorus . Reduced uptake of phosphorus can also be a consequence of the strong influence of sorption processes that control the concentration of phosphorus in the soil and low solubility of Ca-P minerals (Marschner, 1995). Asik, (2009) reported that the uptake of N, P and K of wheat plants decreased when the water salinity increased.
Agronomic Parameters
Analysis of variance indicated that leaf area surface (LAS) , straw and root weight , 100 seeds weight and seed yield per pot of all the genotypes decreased significantly with an increase in salinity(Table 4).LAS tend to decrease as salinity increased, There was a significant difference between genotypes for leaf area under stress
507 and control condition . M/53 had the highest leaf area 1.93 and 0.88 cm2 between genotypes, whilst M/8 and Saber-beg had the lowest leaf area 0.74 and 0.46 cm2 , respectively under low and high saline stress 6 and 14 dsm-1. It is presumed that high levels of Na+ in leaf blades would enhance premature senescence of old leaves and inhibit photosynthetic performance of younger leaves (Benderradji, 2011). In salt-sensitive genotypes, accumulation of salt to toxic
levels in photosynthesizing leaves causes them to fall and in tolerant ones decreases the leaf area (Munns, 2006). At salinity of 6 dsm-1 , the highest straw weight 0.99 g was observed in M/4, whereas the minimum straw weight 0.48 g was observed in M/ 8 (Table 4). But at salinity of 14 dsm-1 , maximum straw weight 0.36 g was found in M/53, whilst minimum in M/4 was 0.21 g. The straw yield was more sensitive to salinity than was the grain yield (Sadeghi and Emam,2011). This finding support that results obtained previously by(Zheng, 2009; Hussein, 2011; Ahmad, 2011) This reverse effect may be due to the retarding effect on photosynthesis (Jampeetong and Brix, 2009), protein building (Parida and Das, 2005), mineral disturbances (Grattan and Grieve, 1999), hormonal balance (Shakirova, 2003), Water adjustment (Shannon, 1997).Saber-beg. Produced maximum root weight 1.5 g.
followed by M/53 1.37 g at 6 dsm-1 salinity, while M/4 produced minimum root weight 1.17g at the same stress level. But at higher salinity level 14 dsm-1, maximum root weight 0.87 g was found in M/53 and minimum 0.50 g in Saber-beg (Table 4). high concentration of Na+ and Cl- ions in the roots medium caused roots growth cease (Al- Mshhadany, 1985; Singh, 1992). At salinity of 6 dsm-1, the best 100 grain weight1.93 g was observed in M/53, whereas the minimum 0.74 g was observed in M/8(Table 4). But at salinity of 14 dsm-1, maximum 100 grain weight 0.91 g was found in M/53, while minimum in Saber-beg was 0.46 g. Data regarding grain yield followed similar trend as was observed in case of 100 grain weight. Again M/53 produced maximum grain yield 10.51 g followed by Saber-beg 10.01 g at 6 dsm-1 salinity, whereas M/8 produced minimum 9.52 g at the same stress level. But at higher salinity level 14 dsm-1, maximum grain yield 4.72 g was found in M/53 and minimum was 3.07 g in M/4(Table 4). These increases in the yield
Table 4. Agronomic parameters and evapotranspiration(ET) of four wheat genotypes Genot types
(G)
EC dsm-1
LAS (cm2)
Straw weight (g) Wt, of 100 (grain) (g)
Root weight (g)
Grain yield (g/plant) ET (cm)
Saber-beg
0.67 2.8 2.82 2.8 4.41 16.05 2.82
6 1.56 0.52 1.56 1.5 10.01 0.52
10 0.81 0.40 0.81 0.67 7.54 0.40
14 0.46 0.33 0.46 0.5 3.45 0.30
x- 1.41 1.02 1.41 1.77 9.39 1.02
M/53
0.67 2.61 2.81 2.8 4.41 16.15 2.81
6 1.93 0.54 1.56 1.5 10.51 0.54
10 0.91 0.48 0.81 0.67 7.28 0.48
14 0.88 0.36 0.46 0.5 4.72 0.36
x- 1.54 1.05 1.41 1.77 9.56 1.05
M/4
0.67 2.85 2.85 2.85 4.38 16.66 2.85
6 1.28 0.99 1.28 1.17 9.57 0.99
10 0.88 0.30 0.88 0.83 6.99 0.30
14 0.72 0.21 0.72 0.75 3.07 0.21
x- 1.46 1.09 1.46 1.78 9.07 1.09
M/8
0.67 1.81 2.53 1.43 3.34 14.18 2.53
6 0.74 0.48 0.74 1.35 9.52 0.48
10 0.65 0.31 0.65 1.01 9.41 0.31
14 0.61 0.26 0.61 0.80 3.77 0.26
x- 0.95 0.90 0.95 1.72 9.22 0.90
S ** ** ** ** ** **
G NS ** ** NS NS **
S X G NS ** NS NS NS *
R NS NS NS NS NS NS
LSD0.05S 1.946 0.174 0.204 0.462 1.285 0.831
LSD0.05G _____ 0.124 0.204 _____ _____ 0.831
LSD0.05SXG _____ 0.348 _____ _____ _____ 1.662
G =Genotypes; S= salinity ; R = replicate ; * , ** indicate. a significant treatment effect as p=0.05 and 0.01, respectively ; NS = Not significant
may be due to the increasing in the weight of grains (Table 4). Singh, (1992) reported the inhibitions of the heads number per plant were responsible of yield reduction. Our results revealed that wheat genotypes responded differently to salinity stress, these results were in line with the finding of AL-Jobori, (2005). However at low level of salinity, it is possible that decrease of leaf area and shoot biomass do not lead to grain yield reduction and the
508 salinity should be reached to a threshold level to decrease the grain yield. Studies on the effects of salt stress on different wheat genotypes have shown that sodium and potassium content and their ratio and shoot dry matter are appropriate traits for screening wheat genotypes for salt tolerance (Goodarzi and Pakniat, 2008). It is also reported that genotype ranking in terms of shoot dry weight lead to the same result as grain yield ranking (El-Hendawy, 2011; Sharbatkhari, 2013). The decline in wheat yield with increasing of salinity level has also been attributed to the accumulation of certain toxic ions (Na+, Cl-) which have a specific ion effect (Francois, 2006; Keshavarz, 2013 ) that could affect on metabolic systems of plants (Faroop and Azam, 2006). Soil salinity reduces crop yield by affecting on equilibrium of water and nutritional characteristics in plants (Faroop and Azam, 2006). screening the salt tolerance of genotypes based on grain yield, which is considered as a final target of both the plant breeder and agronomist(El-Hendawy, 2011).There was a remarkable difference in evapotranspiration (ET) between stress and control treatments , genotypes and genotype × salinity(Table 4). ET tend to decrease as salinity increased, However M/53 genotype had the highest ET 0.36 cm at high salinity level 14 dsm-1, which indicate the efficient of this genotype for water use efficiency under high salt conditions resulting in higher grain yield . Ashraf (2001) found that leaf water potential and evapotranspiration significantly decreased with increasing salt concentration. This agreed with the results obtained by Hu, (2007).
Water Status
A significant difference was observed between salinity stress and control conditions and between genotypes for Leaf water potential, osmotic potential and Turgor pressure, but there was no difference between the genotypes in Turgor pressure (Table 5). Among all genotypes Mutant M/53 showed high leaf water potential and Turgor pressure and decrease osmotic potential than the other genotypes at 14 dsm-1, and that is may be due to the genetic variation between the genotypes.Table 6 showed significant correlation between leaf osmotic potential and ions uptake and salt concentration in irrigated water. These results in agreement with AL-Mshhdany (1985) who found high correlation between leaf osmotic potential and ions uptake, and between osmotic potential and salt concentration in root medium.. The ability of plant to grow and complete its life cycle on saline substrate, appeared to be needed two requirements: (1)osmotic adoption and (2) the acquisition of the mineral elements for growth and functional metabolism. Salt stress markedly reduced different water relation attributes such as leaf osmotic potential (Ψw), water potential (Ψs) and turgor potential (Ψp) of the seedlings of all wheat cultivars. However, relatively less decline in leaf Ψp recorded in cvs. S-24 and G.A-20 could be attributed to their higher degree of salt tolerance (Kanwal, 2013).Increasing osmotic potential under salt stress can be due to high ion absorption and compartmentation of them in vacuole or the presence of osmolytes produced because of osmotic adjustment.
Increase of osmotic potential in sensitive plants is due to decrease in turgor (Perida and Dus, 2005). A primary response to water deficit in salt-tolerant genotypes is osmotic adjustment (Decosta, 2007). While Na+ and Cl− are sequestered in the vacuole of a cell, osmotic adjustment maintains the osmotic equilibrium by accumulation of various compatible osmolytes in cytoplasm such as K+, proline, mannitol and glycinebetaine. It helps the plants keep their stomata open and continue their photosynthesis under salt stress (Munns and Tester, 2008). Under soil salinity, high concentration of Na+ competes with the uptake of other nutrients, especially K+ as a necessary element. Salt-tolerant genotypes of wheat have a more efficient system for selective uptake of K+ over Na+
(Goudarzi and Pakniat, 2008). Reduced solute potential due to saline conditions significantly affects water uptake ability of plants (Munns, 2002) thereby causing water potential more negative which results in reduced growth of most plants (Cha-um, 2010; Eisa, 2012). Osmotic adjustment particularly in leaf is important for plant survival, because it facilitates leaf expansion by maintaining higher stomatal conductance ( Cha-um, 2010; Eisa, 2012), which is considered necessary to sustain photosynthesis in the leaves under salt stress. Low water potential of the saline grown medium causes accumulation of solutes in the cells, which lowers the cell osmotic potential. The reduced cellular osmotic potential is necessary for osmoregulation i.e., maintenance of turgor pressure (Szczerba, 2009; Cha-um, 2010). Osmoregulation is considered as an important mechanism for the normal cell functioning (Taiz & Zeiger, 2010) because maintenance of water status in plant is an essential phenomenon for normal plant growth and development under stressful environments (Ali & Ashraf, 2011). Turgor potential of a cell plays an important role for the normal functioning of metabolic phenomena under adverse environmental conditions (Taiz &
Zeiger, 2002).According to Sohan, (1999), the decrease in water potential can be explained by: 1) the influence of high concentrations of salts due to which plants accumulate more NaCl in the leaves than usual, and 2) by the reduced flow of water from root to aboveground organs due to the reduction of water conductivity, causing water stress
in the tissues of leaves.
509
Table 5. leaf water potential (LΨT), leaf osmotic potential (LΨs) leaf turgor potential (LΨp)of four wheat genotypes Genotypes
(G)
EC dsm-1
LΨT -Mpa
LΨs -Mpa
LΨP +Mpa
Saber-beg
0.67 6 10 14 x-
2.80 0.52 0.40 0.33 1.01
2.82 1.56 0.81 0.46 1.41
0.02 1.04 0.41 0.13 0.44
M/53
0.67 6 10 14 x-
2.82 0.54 0.48 0.36 1.05
2.84 1.93 0.91 0.72 1.60
0.02 1.39 0.43 0.36 0.55
M/4
0.67 6 10 14 x-
2.83 0.99 0.30 0.21 1.08
2.85 1.28 0.88 0.81 1.46
0.02 0.29 0.58 0.60 0.38
M/8
0.67 6 10 14 x-
2.81 0.48 0.31 0.26 0.97
2.83 0.74 0.65 0.61 0.21
0.02 0.26 0.34 0.35 0.24 S
G S X G R LSD0.05 S LSD0.05 G LSD0.05 S X G
**
**
**
NS 0.174 0.124 0.348
**
**
NS NS 0.204 0.204 _______
**
NS NS NS 0.462 _______
_______
G =Genotypes; S= salinity ; R = replicate ; * , ** indicate. a significant treatment effect as p=0.05 and 0.01, respectively ; NS = Not significant
Table 6. correlation coefficient for leaf water potential (LΨT) , and leaf osmotic potential (LΨs) vs. ions uptake EC (dsm-1) Leaf ion content (mMole)
r +
K Na Ca Mg P
0.67 N.S N.S N.S N.S N.S
6 * -* N.S N.S N.S
10 * -* * * -*
14 * -* * * -*
r ++
0.67 * * N.S N.S N.S
6 * * * * *
10 * * * * *
14 * * * * *
* Significance at the 5% level of probability r+ Correlation coefficirnt for (LΨT) vs. ions uptake r++ Correlation coefficirnt for(LΨs) vs. ions uptake
Result of this study lead to conclusion that mutant M/53 had more tolerance ability to saline condition than its origin Saberbeg and other mutants (M/4 and M/8). AL-Mishhadany (1992) found that the tolerance mechanisms were reduction of Na+ concentration , increase K+ , increase K+/Na+ ratio, maintains balance level of Ca+ and Mg+ ion and osmotic potential. In our experiment mutant M/53 haves many of these mechanisms. More ever the results suggested to possible adoption of such physiological and morphological changes(ET, LAS, leaf water and osmotic potentials and K+ accumulation in addition to yield response) as measure of salt tolerance in screening wheat genotypes.
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