| Summary: | Water deficit is a main abiotic stress limiting the cultivation of many plants including cancer bush (<i>Sutherlandia frutescens</i> L.), which is a traditional medicinal plant used to treat various diseases such as tuberculosis, cancer, diabetes and asthma. Natural plant growth hormones are a cost-effective and environmentally friendly alternative to synthetic growth regulators for plant production under favourable or adverse conditions. Thus, the current study investigated the biostimulant effect of moringa (<i>Moringa oleifera</i> L.) seed extract (MSE) on physiological and biochemical attributes, including crop water productivity (<i>CWP</i>) of cancer bush grown under deficit irrigation. The 2% MSE was foliar-sprayed to cancer bush plants subjected to full (100% of soil water holding capacity (<i>SWHC</i>)) and deficit irrigation (DI) (80, 60 and 40% of <i>SWHC</i>) in a pots experiment which was conducted and repeated twice consecutively in a tunnel. Plants that were not treated with MSE were considered as control. The results on water-deficit stress showed that the performance of cancer bush was significantly reduced in terms of growth and yield attributes, <i>CWP</i>, as well as physico-biochemical properties. Nevertheless, the foliar application of MSE on water-stressed plants effectively enhanced growth and yield characteristics, <i>CWP</i>, leaf photosynthetic pigments (chlorophyll “a”, chlorophyll “b”, total chlorophylls and total carotenoids), antioxidant activity (2′-Diphenyl-1-picrylhydrazyl and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid), relative water content (<i>RWC</i>) and membrane stability index (<i>MSI</i>) of cancer bush plants compared to respective controls. Therefore, the 2% MSE application was effective in mitigating negative impact of drought stress in cancer bush plants by maintaining higher <i>RWC</i>, <i>MSI</i>, <i>CWP</i> and biochemical attributes.
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