The present study was conducted during 2004-2006 in the field and in the laboratory conditions to investigate the physiological and biochemical mechanisms of salinity tolerance of different wheat genotypes. The Field experiments were conducted during 2004-05 at three different locations in North West Frontier Province (Yar Hussain, Baboo Dehari (District Mardan), Khitab Koroona (District Charsada) Pakistan, to study the performance of 11 salinity tolerant wheat genotypes (Local, SR-24, SR-25, SR-7, SR-22, SR-4, SR-20, SR-19, SR-2, SR-2, SR-23 and SR-40 for their salinity tolerance. These locations had different salinity profile (i.e. Yar Hussain, EC. 3-3.5 dSm-l; Baboo Dehari, EC. 4.5-5.0 dSm-1 and Khitab Koroona, EC. 5.5-6.0 dSm-1). The laboratory experiments were carried out at NWFP Agricultural University Peshawar, Pakistan during 2005-2006. Various physiological and biochemical characters were studied during the course of both experiment. Statistical analysis of the data obtained from the field revealed that different locations and wheat genotypes had a significant (p < 0.05) effect on plant height, productive tillers m-2, number of grains spike-1, 1000 grain weight, days to anthesis, days to physiological maturity, grain and straw yield, endogenous shoot proline, ABA, Na+, K+ concentration (3, 6 and 9 weeks after emergence). The maximum plant height (84.52 cm ), number of productive tillers m-2 (31.30), number of grains spike-1 (55.33), 1000 grain weight (37.67 g), grain yield (2402 kg ha-1) and straw yield (3495.89 kg ha-1), endogenous shoot proline (652.44, 946.56, 1097.67 m g g-1 fresh weight) and ABA (1.102, 1.133, µg g-1 fresh weight), K+ (0.905, 1.013, 1.040 mg g-1 dry weight) while the minimum Na+ (0.446, 0.713, 1.061 mg g-1 dry weight) concentration 3, 6 and 9 weeks after emergence respectively were recorded in genotype SR-40 followed by genotype SR-23. All the other parameters mentioned above were minimum in the genotype local. The mean data further indicated that maximum plants height (78.50 cm), number of productive tillers m-2 (32.02), number of grains spike-1 (54.33), 1000 grain weight (37.54 g), grain yield (2324.24 kg ha-1) and straw yield (3428.42 kg ha-1) and minimum endogenous shoot proline (473.28, 678.85, 766.49 µg g-1 fresh weight) and ABA (0.866, 0.852, µg g-1 fresh weight), K+ (0.750, 0.797, 0.778 mg g-l dry weight), Na+ (0.553, 0.592, 1.001 mg g-l dry weight) concentration 3, 6 and 9 weeks after emergence respectively were recorded at Yar Hussain. Maximum endogenous shoot proline (473.28, 678.85, 766.49 µg g-1 fresh weight) and ABA (1.116, 1.141, µg g-1 fresh weight), K+ (0.910, 0.972, 1.014 mg g-l dry weight) Na+ (0.618, 0.770, 1.231 mg g-l dry weight) concentration 3, 6 and 9 weeks after emergence respectively were observed at Khitab Koroona.
Data collected and analysed from the laboratory experiment confirmed the findings observed during the field study. Statistical analysis of the laboratory experiment indicated that various physiological and biochemical characteristics of different wheat genotypes were significantly (p < 0.05) affected by genotypes, salinity levels, ABA application and their all possible interactions. Maximum plant height, shoot fresh and dry weight, proline, ABA, K, chlorophyll a and b and carotenoid contents were recorded at control while high salinity levels (10dSm-1) had a negative effect on these parameters. Yield and yield components of various genotypes were significantly reduced due to the exposure of plants to various salinity levels. Among genotypes, SR-40 and SR-23 performed better than the other genotypes under study when exposed to various salinity levels. Exposure of plants to both salinity stress and ABA foliar spray resulted in elevated levels of proline, ABA, chlrorophyll a and b, carorenoid and K+ contents which presumably is involved in cell signaling processes to combat salinity stress.