Effect of Salinity, Selenium and Boron on Chemical Composition of Brassica napus L. plants Grown under Sandy Soil Conditions

Canola is one of the most important medicinal food plants. Salinity induces physiological and metabolic disturbances in plant and causes a great reduction in growth development, yield and chemical constituents. The purpose of this study was to evaluate the impact of salt stress (0, 2.5, 5 and 7.5 dS m-1), selenium (0, 2 and 4 mg l-1 as sodium selenate) and boron (0, 2, and 4 mg l-1 as boric acid) on some chemical composition of canola plants at vegetative and flowering stages grown under sandy soil conditions. The results demonstrated that the lowest level of salinity (2.5 dS m-1) resulted in the highest total soluble phenols, total free amino acids and protein concentrations in leaves of canola plants, while it was decreased with increasing salinity levels. Moreover, increasing salinity levels up to 5.0 and 7.5 dS m-1 increased total sugars, proline and nitrate concentrations. The plants irrigated with salinity up to 5 dS m-1 and sprayed with the highest levels of selenium and boron (4 mg l-1 + 4 mg l-1) recorded the maximum total sugars concentration. The addition of 2 mg l-1 of selenium combined with 2 mg l-1 of boron increased total soluble phenols and protein concentration while increasing boron level to 4 mg l-1 increased total free amino acids concentration in the plants irrigated with the lowest level of salinity (2.5 dS m-1). The plants irrigated with the highest level of salinity (7.5 dS m-1) and sprayed with the lowest level of selenium (2 mg l-1) increased nitrate concentration while proline concentration increased with the highest level of selenium (4 mg l-1). It was clear that selenium and boron played an important role in enhancing the tolerance of the plants to salinity stress. Keywords: Canola, salinity, selenium, boron, chemical constituents.