The tolerance of flax to saline conditions: effect of sodium chloride, calcium chloride, and sodium sulfate

Punjab flax was grown in sand cultures under greenhouse conditions. Thirteen treatments were used including a control or basal nutrient solution (0.5 atm. osmotic concentration) and three series of salt solutions adjusted to 1.5, 2.5, 3.5, and 4.5 atm. osmotic concentration by the addition of NaCl, CaCl2 and, Na2SO4, respectively, to the basal nutrient solution. The vegetative responses of the flax plant to high osmotic concentrations of these salts indicate that it is moderately tolerant to saline conditions. In general, the effect of the three salts on vegetative growth is of the same order at equal osmotic concentrations, but at 4.5 atm. sodium sulfate induced a more pronounced inhibition than the chloride salts. The reduction in height and diameter of stems under high salt treatments is correlated with marked changes in the differentiation of the stem tissues. At high concentrations of salt, the cambium is less active and the cells of the secondary xylem are smaller than in the control plants. The number and diameter of the phloem fibers is also less in plants grown in substrates of high osmotic concentration. As compared with controls, substrates of high osmotic concentration delayed anthesis of flowers and setting of bolls from 5 to 18 days. At equal osmotic concentrations of the three salts the inhibitive effect was most pronounced with sodium sulfate, intermediate with sodium chloride, and least with calcium chloride. Yield of seed was reduced by high salt concentrations in all series. In general, calcium chloride was less inhibitive to seed production than equal osmotic concentrations of sodium sulfate and, with one exception, the effect of sodium chloride was intermediate. At high concentrations of salt (3.5 and 4.5 atm.) relative yields were reduced from 25 to 62% and no mature seed were produced at the highest concentration of sodium sulfate. The effect of the treatments on quality of seed, expressed in terms of seed size, oil content, iodine number, and percentage crude protein, was of questionable significance.