Institute Of Soil And Environmental Sciences \ud =

Scarcity of good quality irrigation water is one of the crop limiting factors inPakistan. Information on the relative tolerance of different crop genotypes is necessary for the successful management of salt affected land and water. To investigate the effect of saline and/or sodic waters on growth, ionic concentration and biochemical changes in sunflower, a series of solution culture and pot experiments were conducted.Initially, 10 sunflower genotypes were grown for 30 days in hydroponics using five levels of saline and/or sodic water;T1 \ud (control), T2 (EC 10.0 dS m-1), T3 (SAR 20.0 mmol L-1)1/2, T4 (RSC 5.4 mmolc L-1), T5 (EC 10.0 dS m-1) + (SAR 20.0 mmol L-1)1/2 + (RSC 5.4 mmolcL-1). On the basis of biomass accumulation and K+: Na+, ratio SF-187 and Hysun-33 emerged as salt tolerant and salt sensitive genotypes respectively. Subsequently, growth and yield response of these genotypes was evaluated in soil culture under various saline and/or sodic water treatments. Although, growth and yield of both genotypes decreased under saline and/or sodic water treatments but SF-187 produced a significantly higher yield as compared to Hysun-33. In the next pot studies, Ca and Si were used @100 mg kg-1 soil to investigate their mitigating effect using same levels of saline and/or sodic water as above. Results revealed that calcium application partially offset the deleteriouseffects of saline and/or sodic waters and improved yield under RSC-water. However, Si significantly improved growth and yield of sunflower \ud under saline and/or sodic water irrigation. The beneficial effec\ud Si were more pronounced in salt sensitive genotypes than in salt tolerant genotypes. Same sunflower genotypes when grown in solution culture, salinized with 100 mM NaCl revealed that 1 mM Si significantly enhanced activities of antioxidant enzymes as compared to 5 mM Ca. Finally, both sunflower genotypes were grown in pot culture and irrigated with saline sodic water.The results confirmed that Si alleviated salt stress and enhanced plant growth \ud stimulating activities of antioxidant enzymes and lowering lipid peroxidation in sunflower.Major mechanisms of Si mediated salt tolerance in sunflower include the maintenance of higher K+/Na+ \ud ratio, reduced membran