Foliar Application of Moringa Seed Extract Alone or in Combination with Salicylic Acid Enhanced Growth, Bioactive, and Phytohormone Compositions of Cancer Bush Plants under Heat Stress

Cancer bush (Lessertia frutescens L.) is an important medicinal plant that is rich in health beneficial compounds. It is commonly used in traditional medicine and as an ornamental plant. Heat stress is the most threatening abiotic factor restricting plant growth, thus causing crop yield and economic losses worldwide. The application of plant-derived biostimulant is as an innovative and promising approach for improving plant growth and productivity. The study was aimed to investigate the effect of moringa (Moringa oleifera Lam.) seed extract (MSE; 5%) either alone or in combination with salicylic acid (SA; 40 mg/L) on the growth, bioactive, and phytohormone attributes of cancer plants subjected to heat stress (38 ^̊C for 2 hours for 5 days). Plants that were not treated were used as control. Plant pots were arranged in a randomized complete block design (RCBD) for treatments (MSE, SA, and MSE + SA) at 7-day intervals during the experiment. Both MSE and MSE + SA foliar application effectively increased plant growth characteristics and total carotenoids contents, and reduced electrolyte leakage and had no symptoms of wilting compared with SA and control. Plants treated with MSE showed higher number of branches and concentrations of abscisic acid (ABA), jasmonic acid (JA), and indole-3-acetic acid (IAA), and lower superoxide and hydrogen peroxide compared with other treatments and control. Also, plants treated with MSE + SA showed higher total chlorophylls and glutathione concentrations compared with other treatments and control. Overall, the application of MSE either alone or in combination with SA enhanced plant growth and productivity of heat-stressed cancer bush plants.