The effect of moringa leaf extract (MLE) on growth and development, mineral composition and antioxidant properties of radish (raphanus sativus) and green beans (phaseolus vulgaris)

Abstract

Besides enhancing food production, one of the major challenges of the agricultural sector is to provide essential minerals and nutrients to humans for the maintenance of a healthy body, not only from a caloric perspective, but also through the provision of antioxidant compounds. It is believed that two-thirds of the world’s plants have medicinal properties and many of these plants have high antioxidant potential. Natural antioxidants, such as flavonoids, vitamin C, tocopherols and other phenolic compounds are known to be present in many plants. Moringa oleifera is one of such plants that has been identified to contain natural antioxidants; particularly the leaves of moringa are a good source of natural antioxidants due to the presence of phenolics, carotenoids, ascorbic acid and flavonoids. While the effect of such plant material on human health has become common subject of investigation, little is known on the effect of moringa leaf extracts applied to plants to enhance their resistance and antioxidant potential. The aim of the experiment was to evaluate the effect of moringa leaf extract (MLE) on the growth and development, mineral composition and antioxidant properties of radish (Raphanus sativus) and green beans (Phaseolus vulgaris). The experiment was laid out in a completely randomized design with five replications and comprised of three treatments, viz. (Control, only inorganic fertilizer Calmag+B (5 g/plant) (T1), common fertilizer plus MLE 100% (T2) (20 g/L dried moringa powder (obtained from Run KZN, Pietermaritzburg, South Africa)) and MLE 50% (T3) (T2 diluted to 50% with 100% methanol). Applications of MLE was carried out during the flowering stage, pod formation stage and prior to harvest. The obtained results demonstrate that MLE applications increased growth and development of both crops (leaf size, pod size, number of flowers, number of matured leaves and, at final harvest, above and below ground fresh and dry mass). Among the various MLE treatments, MLE 50% resulted in higher growth development and yield parameters on both radish and green bean plants compared with the MLE 100% and control plants. The mineral composition of radish leaves, storage roots and

green bean pods was carried out by an independent laboratory. Applications of the treatments had significant influence (p < 0.05) on plants, with MLE-treated plants obtaining higher mineral concentrations compared with the control plants. Treatment with MLE also significantly (p < 0.05) increased antioxidant properties, particularly total antioxidants, anthocyanin, ascorbic acid and total chlorophyll concentrations, with MLE 50% producing plants of the highest overall antioxidant properties. This treatment could, therefore, be possibly employed as a method to obtain healthier, organic vegetables.