Evaluation of Wheat genotypes on the basis of physiological indices under salt stress

Salt stress is one of the major limitations for wheat plant growth and development. Screening of wheat cultivars for salt tolerance is an effective technique to identify tolerant cultivar for salt affected soil. In present study wheat genotypes (Pasban-90 and Frontana) were germinated in petri plates against control, 50mM, 75mM, 100mM, 125mM and 150mM salt levels and root & shoot length, fresh & dry weight, physiological indices like plant height stress indices (PHSI), plant fresh weight stress indices (PFSI), plant dry weight stress indices (PDSI), salt stress tolerance indices (STI), root toxicity (RT), shoot toxicity (ST) and germination energy (GE) were recorded for screening purpose. Root length (27%), shoot length (48%), fresh weight (47%), dry weight (58%), PHSI (38%), PFSI (43%), PDSI (40%), GE (35%) and SSTI (39%) decreased with increasing salt levels. Correlation analysis of all observed traits shows highly positive correlation between PHSI, PFSI, PDSI, STI and GE while significant negative correlation with root and shoot toxicity. On the basis of morphological data and physiological indices Pasban-90 is categorized as a salt tolerant cultivar while Frontana as salt sensitive cultivar.

This study was conducted to identify wheat cultivar that tolerate and survive under salt stress.

Materials and methods
The experiment was carried out at Marker Assisted Selection lab, NIGAB, National Agricultural Research Center, Pakistan.This study was carried out with complete randomized design (CRD) and three replication.Sodium hypochlorite solution was used for surface sterilization of seeds and for this purpose, seeds were dipped in 1% sodium hypochlorite solution for fifteen minutes then washed thoroughly with distilled water and placed in petri plates lined with filter paper.Seeds were germinated in normal condition or different salt levels (50mM, 75mM, 100mM, 125mM & 150mM).Seed were considered germinated when radical length was 5mm
Frontana show maximum reduction in dry weight (64%) at 150mM salt stress while minimum reduction (20%) was observed at 50mM salt levels.Wheat genotypes seed salt stress tolerance indices was decreased at 100 mM and higher salt levels.Salt stress tolerance indices (SSTI) was significantly decreased with increasing salt levels (100mM, 125mM and 150mM).Maximum salt stress tolerance indices was recorded for Pasban-90 (87.2%) at 50mM salt level while minimum SSTI was observed for Frontana (73%) at 50mM.A Pasban-90 salt stress tolerance index was 70% at 100mM and 61% at 150mM though Frontana (53% & 39%) demonstrates least SSTI value (Figure 5).Germination energy (GE) was recorded on the basis of number of seedling emerged and total days of germination (Figure 6).Germination energy was decreased with increasing salt levels and it was 45% at 100mM, 40% at 125mM and 33% at 150mM.Pasban-90 (62%) show maximum germination energy at 50mM salt level while minimum GE was observed for Frontana (50%).Similarly, Seedling Root length, shoot length, gerimination percentage, mean daily germination rate, seedling fresh weight and seedling dry weight considerably reduces under salt stress.Hussain et al.
Introduction Crop plants growth and productivity is considerably affected by different stresses such as water, salt, low temperature and high temperature stress.Salt stress is an important threat to wheat plant productivity and yield [1]. Salt stress is increasing day by day due to poor land practices and improper drainage [2].About eight hundred Mha land in the world and six Mha area in Pakistan is affected due to salinity [3].A high salt level causes ionic and osmotic impact on wheat crop; osmotic stress leads to disturbance in plant water relation and damages membrane stability [4].High sodium in soil competes with potassium and calcium uptake and interrupts cellular ionic homeostasis [5].Wheat is categorized as a major source of energy, grown throughout the world and wheat used as a staple food in Pakistan [3].Pakistan is identified as a fourth in Asia and eleventh in world for wheat production [2].Wheat plant yield drastically decrease with increasing (100mM <) salt levels in soil [6].Osmotic effect of stress negatively affects wheat seed germination and seedling growth [7].Plant acquires tolerance mechanism to withstand salt stress condition and tolerance varies according to crop plant species.Wheat genotypes differ in their tolerance to high salt levels [8] and this information is useful for identification of tolerant cultivars for salt affected soils [2, 9].Many scientists has used physiological indices to identify tolerant cultivar at early stages [3, 7, 10, 11].

[ 4 ].
After 15 days of germination, seedling root and shoot length, fresh and dry weight was recorded and data was used to calculate following physiological indices [3, 4, 12].Salt stress tolerance indices (SSTI) = stressed seedling promptness indices /control seedling promptness indices x 100 Germination energy= N/Tx 100 Where number of seedling over total days.Plant height stress indices = stressed plant length /control plant length x 100 Plant fresh weight stress indices = stressed seedling fresh weight /control seedling fresh weight x 100 Plant dry weight stress indices = stressed seedling dry weight /control seedling dry weight x 100 Shoot toxicity = control plant shoot lengthstressed plant shoot length/control plant shoot lengthx 100 Root toxicity = control plant root lengthstressed plant root length/control plant root length x 100

Figure 2 .
Figure 2. Shoot Length (cm) of wheat cultivars under different salt levels.

Figure 3 .
Figure 3. Fresh Weight (gm) of wheat cultivars under different salt levels [9] finding show that wheat seed germination is interrupted due to increasing salt levels [12, 13].Wheat seed germination delay due to osmotic effect or ionic effect salinity [14, 15] and osmotic effect alters plant water relations and excessive accumulation of Na + or Cl -ions disturbs physiological processes [3, 16].
[11] findings identified that salt stress considerable decrease all physiological indices in which include root length, shoot length, fresh weight and dry weight.Salt stress damage seedling cell membrane as a result sodium ion competes with calcium and potassium ion [17].Ion homeostasis disturbance significantly decreaseseedling growth and development [18].Basalah [19] was recorded considerable decrease in wheat plant fresh and dry weight under salt stress [20].

Figure 8 .
Figure 8. Plant fresh weight stress indices of wheat cultivars under different salt levels

Figure 10 .
Figure 10.Shoot toxicity (%) of wheat cultivars under different salt levels