The effect of shade stress and different growth media on hydroponic-grown trachyandra divaricata (Jacq.) Kunth as a coastal vegetable

Abstract

The objective of the study was to ascertain how vegetative development, nutritional content, phytochemicals, and antioxidant activities of T. divaricata will be affected by different soilless growing media and shade conditions as well as to identify the species' ideal growing protocol. The experiment was run over the course of 12 weeks, Trachyandra divaricata plant divisions were collected from wild populations on the Bellville campus of the Cape Peninsula University of Technology. Divisions of the plants were done to ensure clonal propagation of identical plants. The leaves of all plants were cut to a similar length of 10 cm, measured with a ruler. It was ensured that each plant had the same number of leaves and an equal weight of 23 grams per plant weighed on an electrical scale (g). All plants were then planted into 15 cm pots and placed under controlled irrigation in the propagation house for two weeks after which they were moved to the Nutrient Film Technique (NFT) gutter hydroponic system. Four identically NFT hydroponic systems were constructed with each system being set up on a rectangular wire mesh table (2.5 m long) which provided a flat surface. Another wire mesh table was stacked on top of each table to create a frame which were then covered with different percentages of shading as stated. Each system had its low-density polyethene (LDPE) 50 L reservoir in which the nutrient solution was prepared and supplied to the system. Four Polyvinyl Chloride (PVC) square gutters (2 m long) were placed on each table which held the 15 cm square plastic pots (ten pots per gutter). The gutters were sealed with PVC adhesive to prevent leaks and connected to a 1 × 2000 L/hr submersible pump with 2.5 m head capacity, 20 mm LDPE irrigation piping, 4 × 20 mm elbow irrigation fittings and 4 × 20 mm flow regulators. Water was pumped and circulated continuously from the reservoir tanks which contained a Nutrifeed fertilizer (65 g/kg N, 27 g/kg P, 130 g/kg K, 70 mg/kg Ca, 20 mg/kg Cu, 1500 mg/kg Fe, 10 mg/kg Mo, 22 mg/kg Mg, 240 mg/kg Mn, 75 mg/kg S, 240 mg/kg B and mg/kg Zn. Fertilizer group 1 Reg No: K2025 (Act 36/ 1947) which was bought from Starke Ayres, Cape Town. The pH and electrical conductivity (EC) were maintained at 6.5 and using a Martini Instruments PH55 pH probe. EC levels of the aqueous nutrient solutions were monitored with a calibrated hand-held digital EC meter (Hanna Instruments®™ HI 98312). The nutrient solutions were refreshed every 2 weeks to minimize the build-up of salts in the growing media. The experiment involved two main treatments which were growth media and shading. Four different growth media namely: LECA clay (LC), Consol® silica sand (SS), peat (P) and vermiculite (V) and arranged in a completely randomized block design (CRBD). The silica sand and LECA clay were rinsed thoroughly with sterile water to clean impurities and other earthy materials. The divided parts of T. divaricata were then planted in pots filled with different growing media and placed in a NFT hydroponic system. White shade netting of 20% density was purchased from Stodels Garden Centre, Bellville, South Africa and used to create the shading climates. Different percentages of shading were created with 20% shade cloth by doubling (40%), tripling (60%) and quadrupling (80%) the net into different layers. The control had no shade cover and silica sand (C=0% shade). The study's findings revealed that the use of shade nets and different soilless media had a positive effect on the vegetative growth of T. divaricata, with plants grown under 60% shade in peat medium producing more material than plants grown in no shade. However, leaf length increased significantly in peat soilless medium with no shade. T. divaricata may therefore be cultivated on vermiculite medium under 80% shade for maximum chlorophyll production because it produced the highest chlorophyll content under 80% shade. The optimum treatment for producing phytochemical composition and antioxidant activities in T. divaricata flower buds was moderate shade levels, as the results revealed a considerable rise in silica sand medium with 20% shade. The proximate analysis revealed that the 80% shade level yielded high fats in peat soilless medium. Furthermore, the same tendency was detected in protein yield, which was high in vermiculite under 80% shade, and the similar trend was found in ash content under 80% shade, with silica sand having the greatest value. This experiment clearly shows that T. divaricata can be grown beneath a shade net for optimum production of nutrients. Overall, this work has shown that T. divaricata may be grown in a hydroponic system with various growth media and beneath a shade net. The vegetative development, nutritional content, antioxidant activity, and phytochemical composition in the flower buds of T. divaricata were all positively impacted by various soilless medium in combination with different levels of shade. The accumulation of rich mineral nutrients in flower buds is an indication of a vegetal trait that contributes nutrients. These results indicate that T. divaricata is a promising inflorescence vegetable with excellent nutritional value. It is recommended that the plant should be domesticated and reintroduced as inflorescent vegetable that may could serve as a dietary supplement and might significantly improve food security by providing local communities with enough access to food. Growing T. divaricata hydroponically will also help to availability all year round and mitigate the effects of climate change because crops grown in hydroponic systems are not influenced by seasonality.