Effect of Biostimulant Application on Plant Growth, Chlorophylls and Hydrophilic Antioxidant Activity of Spinach (Spinacia oleracea L.) Grown under Saline Stress

Irrigated agricultural lands are prone to salinity problems which may imperil horticultural crops by reducing growth, yield and even qualitative traits. Eco-friendly approaches such as biostimulant application and in particular protein hydrolysates from vegetal origin are implemented to mitigate salinity stress effects on crops. For this reason, a greenhouse experiment on spinach irrigated with increasing concentrations of saline water (EC = 3 dS m(-1) (EC3), 6 dS m(-1) (EC6) and 9 dS m(-1) (EC9), in addition to non-saline treatment (EC0)) was organized, while plants were subjected to foliar applications of a protein hydrolysate from vegetal origin on a weekly basis. The application of this biostimulant helped mitigate the adverse effects of saline stress, by increasing the SPAD index and total chlorophylls of spinach plants. Yield was significantly boosted under biostimulant treatment in saline conditions and reached the value obtained in control treatment (no biostimulants added) x EC0 in the case of EC 3 and 6 dS m(-1). In addition, the number of leaves and plants m(-1) was increased under biostimulant treatment, and most importantly the hydrophilic antioxidant activity of spinach, thus a qualitative aspect of great importance was also increased. Such results increase the knowledge on the effects of protein hydrolysates application on an important leafy vegetable and may help growers mitigate saline conditions and maintain high crop yield and high quality of the final product when no other source of irrigation water is available.