The present investigation was conducted during the two
successive seasons 2004/2005 and 2005/2006 on onion (Allium cepa L.
cv. Giza 20) grown at the experimental station of the Faculty of
Agriculture, Fayoum University, Egypt, to study the effect of some
antioxidants (ascorbic acid, citric acid, oxalic acid and salicylic acid)
foliar spray at the rate of 0,2.5, 5 and 10 mM on the possibility of
improving growth, yield and some chemical constituents of onion
plants. Significant positive influences of all antioxidants treatments
used in this study were observed on growth, yield of bulb and some
chemical composition characters in both tested seasons. The obtained
results indicated that, the growth characters, i.e. plant height, number
of leaves/plant, and fresh and dry weight of leaves/plant were affected
positively by the application of all antioxidants used at all studied rates.
The maximum increase in this respect was obtained by the treatment of
10 mM followed by 5 mM treatment as compared to the control
untreated plants in both seasons. The same treatments increased bulb
yield and its components (bulb diameter, as well as fresh and dry
weight of bulb). In addition the most effective treatments for enhancing
the concentration of chlorophyll a and b, total caroteniods, total free
amino acid, total indoles, and total soluble phenols on fresh leaves, and
total carbohydrates, total and reducing sugars, anthocyanin
concentration, crude protein and some nutrients i.e. N,P and K in dry
matter of leaves and the content of bulbs from total soluble solids
(T.S.S.%), total soluble carbohydrates and protein was observed at
higher concentration (10mM) of all antioxidants used especially
Ascorbic acid and Salicylic acid. Thus, the highest application of
antioxidants is recommended for improving growth, yield and
chemical composition of onion plants.