The extensive use of synthetic chemical fertilizers is associated with environmental pollution and soil degradation. In addition, the high costs of these fertilizers necessitate the search for alternative, eco-friendly and safe natural sources of phytonutrients. The liquid extracted from moringa (Moringa oleifera Lam.) leaves has been used in agriculture to improve the growth and productivity of several crops. The efficacy of moringa leaf extract (MLE) is attributed to its high content of mineral nutrients, protein, vitamins, sugars, fiber, phenolics and free proline. In addition, MLE contains significant amounts of phytohormones, such as auxins, cytokinins and gibberellins. Furthermore, MLE is a valuable product promoting seed germination, plant growth and deeper root development, delaying fruit senescence and increasing the yield and quality of crops grown under normal or stressful conditions. Here, we review the research on MLE as a biostimulant to enhance crop growth and productivity. Moreover, we emphasize its possible introduction to smallholder farming systems to provide phytonutrients, and we further highlight research gaps in the existing knowledge regarding MLE application. Generally, MLE is an inexpensive, sustainable, eco-friendly and natural biostimulant that can be used to improve the growth and productivity attributes of various crops under non-stressful and stressful conditions.

The prevention of certain chronic diseases has been related to tomato (Solanum lycopersicum L.) consumption. The demand for high-quality tomatoes has, therefore, increased rapidly. As a climacteric fruit, tomato will only ripen to full colour postharvest. Trusses of mature-green greenhouse tomatoes of a red (‘Cherry Little Wonder’) and a yellow cultivar (‘Goldilocks’) were illuminated, preharvest, with either red (RL) (peak at 634 nm, 120 ± 20 µmol m^–2 s^–1) or blue (BL) LED lights (peak at 450 nm, 120 ± 20 µmol m^–2 s^–1) for 8 h per day for seven consecutive days. These on-plant RL and BL treatments significantly affected fruit colour and pigment concentration. Both light treatments enhanced the accumulation of lycopene, thereby significantly enhancing the nutritive value of the fruit. Similarly to lycopene, the β-carotene concentrations also increased following RL and BL exposure, again more so in the red than the yellow cultivar. Both light treatments also enhanced the speed of colour change by 5 days for the red and by 10 days for the yellow cultivar, resulting in either the desired red or the yellow colour. Our findings could be employed to improve quality and shorten the ripening period of tomato, while mechanisms involved in the biosynthesis and accumulation of these carotenoids require further investigation.

Green-mature and turning cherry tomatoes (Solanum lycopersicum L.) of a red (‘Cherry Little Wonder’) and a yellow (‘Goldilocks’) cultivar (cv) were illuminated, post-harvest, with either red (118 µmol m^–2 s – ¹ at 638 nm) or blue LED light (118 µmol m^–2 s – ¹ at 454 nm) for 48 h and subsequently stored for up to 21 days at room temperature. The effects of the treatments on colour, firmness, sugars and carotenoids were evaluated throughout storage. The light treatments did not have any effect on firmness and mass; however, light exposure, particularly red light, enhanced the a* colour component of the red cv significantly; similarly, colour coordinate b* of the yellow cv, treated at both stages of development, was significantly enhanced by both light treatments, resulting in visually redder and yellower tomatoes, respectively. These effects were more so observed on green-mature than on turning fruit. In addition, the treatments significantly increased lycopene concentrations in the red cv at both ripening stages, and β-carotene concentrations in both, the yellow and red cv treated at the green-mature stage. Total soluble solids (%TSS) also increased significantly following treatment. Findings reported suggest that illuminating tomato fruit with LED lights at the green-mature stage enhances colour development and the concentration of sugars, pigments and other health-related compounds without significantly affecting fruit mass and firmness.

The majority of losses in horticultural produce occur during postharvest storage, particularly due to poor handling. Most fruit, especially climacteric fruit, have a short postharvest life due to an increase in ethylene synthesis which signals ripening and, subsequently, senescence. Traditional practices for preserving the postharvest quality of horticultural crops are chemical-based, a practice which has lately received enormous criticism. Recently, the use of postharvest illumination with LEDs as a nonchemical and environmentally friendly technique to preserve fruit and vegetables has been reported by various authors. Unique properties of LEDs such as low radiant heat, monochromatic nature and low cost have made this lighting gain popularity in the food industry. This paper, therefore, reviews the recent development in the postharvest applications of LEDs in horticultural crops, while focusing particularly on physical characteristics, nutritional value, and overall quality alterations of fruit and vegetables. According to the recently published research, red and blue LED lights are most valuable in terms of usage, while other wavelengths such as purple and yellow are slowly gaining attention. Furthermore, LEDs have been shown to affect fruit ripening and senescence, enhance bioactive compounds and antioxidants in produce, and prevent disease occurrence; however, there are some limitations associated with the use of this novel technology.