Interactive effect of Mg and shading on the yield, physiology and antioxidant activity in cucumber grown in hydroponics

An experiment was carried out to evaluate the effect of various concentrations of Mg (0, 1, 2, 3 and 4 mM) in the nutrient solution and shading (0 and 50%) on growth, yield, fruit quality and physiological properties in hydroponically grown cucumber (Cucumis sativus L. cv. Nagen 792). With increased Mg concentration in both shaded and unshaded plants, the total plant leaf area and dry weight of leaves increased, whereas specific leaf weight decreased. The highest yield in terms of fruit weight and number per plant in both shaded and unshaded plants were obtained in 3 mM Mg treatment; however yield in shaded plants was 57% that of in unshaded plants. Increased Mg concentration drastically increased Mg content and reduced K and Ca content in the leaves and fruits, particular in shaded plants. Leaf and fruit concentration of Mg increased drastically while K and Ca decreased with increasing Mg in the nutrient solution. The activity of ascorbate peroxidase (APX) and peroxidase (POX) in the leaves was decreased by increasing of Mg concentration. The highest activity of APX and POX was observed in Mg deficiency plants and it becomes more pronounced in unshaded plants. Leaf soluble sugars and starch content were decreased with increasing Mg concentration in the solution, especially in shaded plants. Low Mg concentration in the nutrient solution significantly increased total free amino acids (FAA) in the leaves. In conclusion, Mg requirement of cucumber plants likely increases with light intensity. Thus, higher concentration of Mg (3 mM) in the nutrient solution was the most favorable for cucumber plant growth and function grown in hydroponics.