2.1. Plant materials and experimental design

The experiment was conducted in the greenhouse at the Plant Production Department, College of Food and Agriculture Sciences, King Saud University, to investigate growth and physiological and biochemical changes of wheat plants developing under salt stress. Six wheat genotypes, including three cultivars, viz., Sakha-93 (salt-tolerant), Giza-168 (salt-moderate), and Gemmeiza-9 (salt-sensitive), and three DHLs, viz., DHL21, DHL7, and DHL2 (as novel high-yield genotypes), were used in this study. The grains of cultivars were obtained from the Agricultural Research Center, Egypt, and the grains of DHLs were obtained from the Department of Agronomy, Faculty of Agriculture, Al-Azhar University, Cairo, Egypt (El-Hennawy et al., 2011). Three salinity (NaCl) levels (control (washed sand), 7 and 14 dS m⁻¹) in the soil were applied at the beginning of the experiment. The grains of these six genotypes were germinated in freshwater to avoid an osmotic shock. Five plantlets from each genotype were planted under three salinity levels in plastic pots filled with sand. The field capacity 70% was achieved by adding tap water or salt solution to each pot. The nutrients were provided using 25% Hoagland’s nutrient solution. Growing conditions in the greenhouse were 23 ± 2 °C during the day and 16 ± 2 °C during the night, with a photoperiod cycle of 16-h light and 8-h dark and a light intensity of approximately 60 μmol m⁻² s⁻¹. Salinity levels were modified four times during the experiment period due to the up-take of salt by plants. A completely randomized design was used in this study. The experiment was replicated six times, with 30 grains for each of the six genotypes and replicates (n = 5 plants or samples per genotype in each treatment). The seedlings were harvested after 45 days from planting (at the first signs of death in the sensitive genotypes), and growth and physiological and biochemical measurements were recorded.