Abstract
Natural extracts and biostimulants have recently been used to enhance growth and productivity of stressed plants. A pots trial was performed to verify the impacts of maize grain (MgE, 60 g L-1) and/or propolis (PrmE, 40 g L-1) extract foliar application (three times) on growth, physio-biochemical attributes, and productivity of faba bean plants exposed to drought (40% of soil capacity), salinity (150 mM NaCl), or cadmium (2.0 mM Cd2+) stress versus absence of stress as a control. Alterations in the antioxidant system and its relationship with stress tolerance were also examined. The results indicated that each stress caused a significant decrease in yield traits, photosynthetic efficiency, pigment contents, gas exchange, relative water content, membrane stability index, and osmolyte contents compared to non-stressed plants. Otherwise, MgE and/or PrmE enhanced the plant's stress tolerance and increased the aforementioned attributes under normal or stress conditions. Moreover, MgE and/or PrmE increased enzymatic activities (SOD, CAT, POX, and APX) and antioxidant levels (proline, glutathione, ascorbate, and alpha-tocopherol) under the studied stresses compared to untreated controls. The combined MgE+PrmE was the most efficient treatment. Salinity considerably increased Na+ content, whereas, MgE+PrmE treatment reduced Na content by 39.6, 16.7, or 37.0% under salinity, drought, or Cd2+ stress, respectively. Under Cd2+ stress, the best treatment (MgE+PrmE) reduced root and leaf Cd2+ contents by 74.1 and 78.6%, respectively compared to untreated plants. Our findings indicated that foliarly-applied MgE+PrmE was highly effective in enhancing the antioxidant machinery, thus reducing ROS, Na+, and Cd2+ levels resulting in increased plant productivity under salinity, drought, or Cd2+ stress.