PHYSIOLOGICAL-RESPONSES OF CANOLA AND WILD MUSTARD TO SALINITY AND CONTRASTING CALCIUM SUPPLY

Growth, ion balance, water relations and leaf photosynthesis of canola (Brassica napus L., cv. Excel) and wild mustard (Brassica kaber L. C. Wheeler) grown under a mixture of sodium and magnesium sulphate salts were examined using a hydroponic system in a growth chamber. Wild mustard was less salt tolerant than canola, based on the growth responses. Salinity caused large accumulation of sodium (Na) and magnesium (Mg) ions, but reduced calcium (Ca) and potassium (K) concentrations in the shoots and roots. Water potential, osmotic potential, transpiration, stomatal conductance and hydraulic conductance decreased to a greater extent in canola than in wild mustard, indicating salinity imposed a smaller osmotic effect on the wild species. Calcium addition improved the growth of wild mustard more than canola but it had no effect on water relations. The growth reduction in these species under salt stress resulted from a combination of ion toxicity, insufficient nutrient ion availability and altered water relations. Supplemental Ca improved growth by reducing Mg and increasing Ca content in plant tissues, ameliorating salinity-associated ion toxicity to photosynthesis, and possibly through an indirect effect on cell growth.