MITIGATING SALT STRESS EFFECTS BY EXOGENOUS APPLICATION OF PROLINE AND YEAST EXTRACT ON MORPHO-PHYSIOLOGICAL, BIOCHEMICAL AND ANATOMICAL CHARACTERS OF CALENDULA PLANTS

To avoid the hazard effect of salinity on calendula (Calendula officinalis L.), two field experiments were carried out at Sahl El-Husseinieh Research Station, Al-Sharqia Governorate, Egypt during two successive winter seasons of 2017/2018 and 2018/2019 in silty clay soil to evaluate the effects of foliar spraying with yeast at 0, 4, 8 and 12 g l-1, proline at 0, 50, 75 and 100 mg l-1 and the interaction between them. The obtained results showed that foliar application of proline, yeast and their interactions led to improve and increase plant growth, floral, physiological and biochemical characters of calendula plants significantly more than those obtained by control, such as plant height, number of branches plant-1, plant fresh and dry weights, number of flowers plant-1, flowers fresh and dry weight, relative water content, carotenoid, total chlorophyll, proline content in plant leaves, as well as the activity of PPO, POX and CAT. Also, the above treatments led to improve calendula plant growth by reducing the activity of both superoxide and hydrogen peroxide and decreasing EL. Application of proline, yeast and their interactions increased the elements content of calendula plant for N, P, K, Ca and Mg %. In the contrary, they decreased Na % in the plant. Results showed that vegetative growth, floral parameters as well as anatomical characters of leaves were significantly decreased under salt stress conditions. The physiological and biochemical characters such as photosynthetic pigments content, relative water content (RWC %) and mineral elements (N, P, K, Ca and Mg %) in the leaves also significantly decreased. Whereas, Na %, proline concentration, the activity of (O-2 and H2O2) and electrolyte leakage (EL %) were increased. Moreover, available N, P and K (mg kg-1) in the soil is negatively affected by salt stress. The combined treatments of proline at 100 mg l-1 + yeast at 12 g l-1 followed by proline at 100 mg l-1 + yeast at 8 g l-1 gave the higher values of plant growth, biochemical and elemental content in plant besides improved the anatomical characters, consequently, increased the tolerance of calendula plants to salt stress under field conditions.