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 mus tard 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 th e 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 wa ter relations. The growth reduction in these species under salt stress resulted from a combination of ion toxicity, insufficient nutrient io n availability and altered water relations. Supplemental Ca improved g rowth by reducing Mg and increasing Ca content in plant tissues, ameli orating salinity-associated ion toxicity to photosynthesis, and possib ly through an indirect effect on cell growth.