An Overview of the Recent Developments in the Postharvest Application of Light-emitting Diodes (LEDs) in Horticulture

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

The potential of postharvest silicon dips to regulate phenolics in citrus peel as a method to mitigate chilling injury in lemons

This study investigated the ability of silicon dips to enhance the phenolic content in order to reduce the incidence of chilling injury in lemon fruit. Fruits were obtained from two farms and dipped in 0, 50, 150 and 250 mg L-1 solutions of K2SiO3 for 30 min and afterward, fruit were air dried and waxed. Thereafter, fruits were stored at -0.5°C and sampled after 28 days for evaluation of phenolic content and chilling injury symptoms. Chilling susceptible fruit sourced from Ithala farm had significantly lower phenolics and flavonoids concentration when compared with chilling resistant lemons from Ukulinga farm. Phenolic and flavonoids content was improved by dipping fruit in silicon for almost all the concentrations. Moreover, 50 mg L-1 reduced the occurrence of chilling injury symptoms whilst high silicon concentrations increased chilling injury. In conclusion, silicon dips have an ability to reduce chilling injury symptoms in lemons; however, low concentrations should be used.Keywords: Silicon, lemon, antioxidants, phenolics, chilling injuryAfrican Journal of Biotechnology, Vol. 12(13), pp. 1482-148

Symplastic solute transport and avocado fruit development : a decline in cytokinin/ABA ratio is related to appearance of the Hass small fruit variant

Studies on the effect of fruit size on endogenous ABA and isopentenyladenine (iP) in developing avocado (Persea americana Mill. cv. Hass) fruit revealed that ABA content was negatively correlated with fruit size whilst the iP/ABA ratio showed a linear relationship with increasing size of fruit harvested 226 d after full bloom. The effect of this change in hormone balance on the relationship between symplastic solute transport and appearance of the small fruit variant was examined following manipulation of the endogenous cytokinin (CK)/ABA ratio. Application of ABA caused seed coat senescence and retarded fruit growth but these effects were absent in fruit treated with equal amounts of ABA plus iP. Thus, the underlying physiological mechanisms associated with ABA-induced retardation of Hass avocado fruit growth appeared to be inextricably linked to a decline in CK content and included: diminution of mesocarp and seed coat plasmodesmatal branching, gating of mesocarp and seed coat plasmodesmata by deposition of electron dense material in the neck region, abolishment of the electrochemical gradient between mesocarp and seed coat parenchyma, and arrest of cell-to-cell chemical communication

Foliar Application with Plant-Derived Extracts Enhances Growth, Physiological Parameters, and Yield of Potatoes (<i>Solanum tuberosum</i> L.)

The current reliance on pesticides and synthetic fertilizers has been vital to sustain and even increase agricultural production. The continuous, excessive use of these traditional practices has negatively affected consumers’ health and burdened ecosystems. The use of plant extracts has the ability to improve plant growth and agricultural productivity. This study was, therefore, conducted to determine the effects of foliar plant extract application on potato growth, as well as on certain physiological and yield attributes. The treatments included extracts of the seaweed Ascophyllum nodosum, aloe vera leaves, garlic bulbs and moringa leaves. From four weeks after planting onwards, five healthy, equal-sized potato plants received 50 mL of the above-mentioned plant extracts as foliar applications. These treatments were repeated weekly until harvesting. Data on growth and physiological parameters were collected weekly. Pre-harvest foliar application of various plant extracts significantly enhanced (p ≤ 0.05) the plant growth and yield attributes of the potatoes. The best growth and yield responses were observed following ANE and MLE applications. A positive influence of various foliar plant extract applications on the growth and yield of potatoes was demonstrated. Further validation of the response of other crops is still necessary to promote the adoption of this approach

Alterations in yield, physicochemical components and mineral composition of onion following organic manure and inorganic nitrogen application

Onion is the one of the most important vegetable crops grown extensively throughout the world; hence, understanding the response of the crop to the form and amount of N provided is of immense importance. In a field experiment, poultry and cattle manure (at 10 t/ha) were compared with four inorganic nitrogen (N) application levels (0, 60, 90 and 120 kg N/ha), and six combinations of manure and N applications were investigated. Plant growth and total yield (kg/ha) significantly increased, when N application increased from 0 to 120 kg/ha, with or without added poultry manure. Plant height, leaf number and neck thickness were significantly reduced at 0 kg/ha N plus cattle manure. The bulb ascorbic acid concentration significantly increased with the use of poultry manure (15.94 mg/100 g) and cattle manure (15.94 mg/100 g), compared with 120 kg/ha inorganic N (11.42 mg/100 g). No significant effects were observed on total phenolics and total soluble solids of onion bulbs following the different fertiliser treatments. Cattle manure increased P and K concentrations, whilst poultry manure significantly increased Zn and Fe concentrations in onion bulbs. Onion bulb Ca and Mg concentrations were lower when cattle manure (0.19% and 0.12%) was used than when other organic or inorganic fertilisers were used. Therefore, organic manure increases the concentrations of certain minerals in onions, compared with inorganic N application, without negatively affecting bulb size

Assessing the Usefulness of <i>Moringa oleifera</i> Leaf Extract as a Biostimulant to Supplement Synthetic Fertilizers: A Review

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

Symplastic solute transport and avocado fruit development : a decline in cytokinin/ABA ratio is related to appearance of the Hass small fruit variant

Studies on the effect of fruit size on endogenous ABA and isopentenyladenine (iP) in developing avocado (Persea americana Mill. cv. Hass) fruit revealed that ABA content was negatively correlated with fruit size whilst the iP/ABA ratio showed a linear relationship with increasing size of fruit harvested 226 d after full bloom. The effect of this change in hormone balance on the relationship between symplastic solute transport and appearance of the small fruit variant was examined following manipulation of the endogenous cytokinin (CK)/ABA ratio. Application of ABA caused seed coat senescence and retarded fruit growth but these effects were absent in fruit treated with equal amounts of ABA plus iP. Thus, the underlying physiological mechanisms associated with ABA-induced retardation of Hass avocado fruit growth appeared to be inextricably linked to a decline in CK content and included: diminution of mesocarp and seed coat plasmodesmatal branching, gating of mesocarp and seed coat plasmodesmata by deposition of electron dense material in the neck region, abolishment of the electrochemical gradient between mesocarp and seed coat parenchyma, and arrest of cell-to-cell chemical communication