INFLUENCE OF ARBUSCULAR MYCORRHIZAL FUNGI AND AMMONIUM:NITRATE RATIOS ON GROWTH AND PUNGENCY OF SPRING ONION PLANTS

A pot experiment was carried out to study the growth and pungency of Allium fisutulosum grown in Perlite as affected by colonization by the arbuscular mycorrhizal (AM) fungi Glomus etunicatum, Glomus vesiforme, and by ammonium (NH⁺ ₄ ):nitrate (NO^? ₃ ) ratios of 5:95, 50:50, and 95:5 in 4 mM solutions. Plants were grown in a greenhouse for 20 weeks and then harvested. In general, NH⁺ ₄ :NO^? ₃ ratio of 50:50 supplied resulted in the highest shoot dry weight regardless of non-mycorrhizal and mycorrhizal plants while the effect of inoculation treatment on plant biomass was not significant. The plant sulfur (S) concentrations were usually higher in mycorrhizal plants than controls irrespective of nitrogen ratio and therefore inoculation with G. etunicatum increased the enzyme produced pyruvic acid (EPY) while inoculation with G. versiforme decreased the EPY compared with the non-mycorrhizal plants. In general, shoot pungency was lowest when NH⁺ ₄ :NO^? ₃ ratio of 95:5 supplied irrespective of mycorrhizal treatment. Colonization by both AM fungi made a substantial contribution to spring onion sulfur nutrient status but show different way on flavor characteristics of host plants.