Changes in antioxidants and pungency in response to foliar applications of Mn and Fe in onion

The aim of the present work was to study the changes in antioxidants and pungency in response to foliar applications of Mn [manganese: Mn1(0%); Mn2(0.5%); Mn3(1.0%)] and Fe [iron: Fe1(0%); Fe2(0.5%); Fe3(1.0%)] in onion genotype Sukhsagar (Allium cepa L.); a field experiment in factorial randomized block design with three replications was conducted in research farm of Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal, India. In this experiment, we observed that the total and free phenol contents were significantly higher than control in both the single (0.5%) and double (1.0%) doses of Fe alone. Again, the activity of enzymatic antioxidant super oxide dismutase (SOD) increased with increasing doses of Fe alone, while the maximum peroxidase (POD) activity was obtained in the treatment combination of double doses (1.0%) of both Fe and Mn. The highest dose of Mn (1%) in combination with all doses of Fe (0, 0.5 and 1.0%) exhibited the highest set of values of catalase (CAT) activity.  The activity of 2,2-diphenyl-β-picrylhydrazyl radical scavenging activity (DPPHRAC) assay increased with increasing doses of Fe. The lowest degree of lipid peroxidation was observed in the case of 1% Mn in combination with 1% Fe, which also exhibited the highest pungency. The average values of all the parameters along with the results of PCA, the treatment Mn3Fe3 (the double dose or 1.0% both of Fe and Mn) was found to be the most efficient to ensure the antioxidant properties of the genotype Sukhsagar. Key words: Allium cepa L., manganese, iron, antioxidants, pungency.