Influence of Boron and Salicylic Acid on Some Vegetative and Biochemical Traits of Lettuce (Lactuca sativa L.) in Hydroponic Syste

Boron (B) is an essential microelement in higher plants, but excessive amount of B in the soil or in irrigation water create serious problems on plant growth, production and human health. Salicylic Acid (SA) plays a key role in establishing and signaling a defence response against various environmental stresses. Exogenous application of SA may alleviate adverse effects of B toxicity in lettuce )Lactuca sativa L.( In this experiment, in order to evaluate effect of B and SA on morphological and biochemical traits of lettuce, an experiment was carried out as factorial based on completely randomized design with three replications in 2017. Experimental treatments included three levels of SA (0, 0.5 and 1 mM) and three levels of B (0.05, 0.5 and 1 mM). The results revealed that with increasing B concentration in nutrient solution decreased leaf fresh and dry weight, leaf area, and chlorophyll a, b, total and carotenoid contents. The highest contents of proline, soluble sugar, total phenol and electrolyte leakage were obtained in plants fed with concentration of 1 mM B and SA, and the lowest value in B and SA control treatments. The maximum of ascorbate peroxidase (APX) and peroxidase (POX) activity in the leaves was recorded at concentration of 0.5 and 1 mM B in solution, respectively. The increase in B concentration in the nutrient solution from 0.05 mM to 1 mM the leaf B content increased 9.3 times. The results this experiment showed that B excess significantly decreased growth and yield of lettuce and SA foliar application cannot alleviate B toxicity in lettuce.