Abstract
Tomato (Lycopersicon esculentum Mill.) is an important commercial crop. High quality tomatoes for the local and export markets are grown hydroponically. In this study, the effect of electrically activated sodium bicarbonate and non-ionized sodium bicarbonate solutions on productivity and postharvest quality of hydroponically grown tomatoes was tested. Sodium bicarbonate is a ready source of bicarbonate. By using a novel technique obtained from Radical Waters (Pty) Ltd., ionized bicarbonate (anolyte) can be produced from sodium bicarbonate and applied to plants to stimulate photosynthesis, and improve yield and postharvest quality. The effect of ionized and non-ionized bicarbonate solutions on productivity and postharvest quality was studied by measuring the following: (1) Preharvest growth rate (leaf length, stem height and diameter); total yield; starch concentration in leaves; fruit count; leaf chlorophyll content; CO2-uptake; soluble solids and concentration of K+, Na+ and NO3¯ in leaves. (2) Postharvest rate of respiration and transpiration; ethylene production; total soluble solids content; ascorbic acid content; pH; fruit firmness; fruit mass; fruit diameter; longevity; concentration of K+, Na+ and NO3¯ at one-third towards maturity, two-thirds towards maturity, at maturity and during ripening, and rate of ripening at 12 and 23°C. During the preharvest period, plants treated with anolyte showed increased growth rate, starch concentration, chlorophyll content, soluble solids content and improved yield. During the growth period, the concentration of K+ and NO3¯ was higher in plants treated with anolyte than in plants treated with non-ionized sodium bicarbonate. The concentration of Na+ during the preharvest period was higher in plants treated with non-ionized sodium bicarbonate than in plants treated with anolyte. After harvest, fruits from plants treated with anolyte had a reduced rate of ethylene production, rate of respiration and transpiration, total increased soluble solids and ascorbic acid content than fruits from plants treated with non-ionized sodium bicarbonate. Fruits from plants treated with anolyte had reduced rate of ripening and were larger and heavier than fruits from plants treated with non-ionized sodium bicarbonate. Anatomical and ultrastructural studies revealed that treatment with anolyte stimulated cell growth and photosynthesis. These results were confirmed by comparing the CO2-uptake of treated and untreated plants. Application of anolyte stimulated photosynthesis, thus improving yield and fruit quality. Treatment with non-ionized
sodium bicarbonate resulted in salt- stress and calcium deficiency. Some of the fruits on plants treated with non-ionized sodium bicarbonate suffered from blossom-end rot due to salt-stress.
Prof. C.S. Whitehead