|Keywords (Extracted from title, table of contents and abstract of thesis)
salt tolerance, barley, hordeum vulgare l, wheat, triticum aestivum l, lyllpur-73, pak-81, lu-26, pasban-90, landrace, capelle, roughrider, salinity,salt-affected soils
Four cultivars of Hordeum vulgare L. differing in salinity tolerance, viz. Haider-93 and Jau-87 (tolerant), Frontier-87 (medium sensitive) and Jau-83 (sensitive) along with five genotypes of Triticum aestivum L., viz. Lyllpur-73 Pak-81 (tolerant and medium tolerant), Lu-26 (medium sensitive), Pasban-90 and Landrace (sensitive) were investigated during the present study. Besides, two exotic wheat varieties differing in proline content and frost tolerance, i.e. Capelle (low proline content and less frost tolerant) and Roughrider (high proline content and highly frost tolerant) were also evaluated. These wheat and barley varieties were investigated for changes in water and osmotic potential, stomatal resistance, chlorophyll fluorescence (Rfa-values), accumulation of Na+ and Cl- ions and proline, grain yield and biomass under salinity stress. The plants were subjected to increasing concentrations of salt viz. 75mM. 150mM, 300mM and 400mM NaCl at the three leaf stage under growth chamber, natural climatic and field conditions.
The first experiment was conducted in a growth chamber. The results revealed that increasing concentrations of NaCl had significant detrimental effects on the physiological parameters, particularly in the salt sensitive cultivars of barley viz., Jau-83 and Frontier 87, as well as in the salt sensitive cultivars of wheat viz. Landrace, Pasban 90 and Lu-26. The tolerant lines of barley viz. Jau-87 and Haider-93 and that of wheat viz. Pak-81 and Lyllpur-73 were less affected by NaCl treatments and exhibited better performance in terms of physiological parameters. The Canadian wheat variety with high frost tolerance, Roughrider proved to be salt sensitive in comparison to the frost sensitive. French variety Capelle, which was found to be more salt tolerant. At lower concentrations of NaCl. viz. 75mM, and 150mM, small effects were observed with regard to stomatal resistance, osmotic potential. Rfd-values and proline contents. At higher doses of salt i.e., 300mM and 400mM NaCl, the sensitive cultivars of barley viz. Jau-83 and Frontier-87 and there of the wheat varieties viz. Landrace, Roughrider and Pasban-90 showed marked reductions in water and osmotic potentials, decrease in Rfd-values, increase in diffusive resistance and less proline accumulation. The proline contents were significantly increased (p<0.001) in the resistant lines of wheat viz. cv. Pak-81, Lyllpur-73 and Capelle and barley viz. Jau-87 and Haider-93 with increasing concentrations of NaCI.
The tolerant lines in both crops exhibited greater Na+ contents than the sensitive lines. Higher concentration of sodium in the salt resistant genotypes of wheat and barley seem to be related to the transpirational pull. This view is supported by the observation that the salt tolerant genotypes exhibited less stomatal resistance.
The second experiment involved the evaluation of the selected wheat and barley varieties cultivated in pots under natural climatic conditions of Pakistan. The results obtained were similar to those found in controlled conditions, but the magnitude of responses varied depending on other environmental factors, viz. humidity, light intensity, temperature etc. which may have mitigated the adverse effects of salinity stress. The tolerant cultivars of wheat and barley accumulated more proline, showed less inhibition in fresh and dry weight, the number of tillers per plant and 100 seed weight under NaCl stress. The two exotic cultivars of wheat, Roughrider and Capelle, exhibited different behavior under NaCl stress. Roughrider behaved as sensitive to salt and Capelle, as salt resistant. These result confirm the finding when tested in the growth chamber conditions This observation, also indicates that frost tolerance is not necessarily correlated with salinity tolerance.
The third experiment was aimed at investigating the wheat and barley cultivars in four different salt-affected regions of Punjab. The proline contents accumulated more at higher EC value of saline soils particularly in the tolerant varieties of wheat and barley. The stomatal resistance was increased significantly (p<0.001) with higher EC values, particularly for the salt susceptible cultivars. The tolerant genotypes of both crops exhibited greater number of tillers and seed weight at EC values ranging from 8.3-12.5 dsm-1. They also showed comparatively higher proline contents, greater Na . and Cl uptake with higher stomatal resistance at the reproductive stage than at the vegetative phase. In barley and wheat salt tolerance was related to a better water status and the ability for pronounced accumulation of proline under saline conditions as compared to the salt susceptible ones.
It is concluded from the findings of these three experiments that a relationship exists between genotype- specific salinity tolerance and accumulation of proline in the leaves and roots along with higher uptake of sodium and chloride, lower decrease in the water and osmotic potentials less inhibition in the Rfd-values as well as yield under salinity stress.