Abstract: SH₄₀ and Balenghaitang (Malus micromalus) , apple rootstocks, were used as experimental materials to study the organic acid exudation from roots grown hydroponically under iron-deficiency stress. Results showed no difference in types of organic acids between SH₄₀ and Balenghaitang under iron-deficiency, including oxalate, malonic acid, tartaric acid, citrate acid and malate. The quantity, however, was significantly different. The total amount of organic acid of Balenghaitang, which has higher in iron-deficiency tolerance,was higher than that of SH₄₀. On the other hand, oxalate and citrate exuded from SH₄₀ and Balenghaitang were increased largely under iron2deficiency stress, and drymass and Fe content of Balenghaitangwere significantly higher than that of SH₄₀. In summary, significantly increased oxalate and citrate exudation is probably responsible for the tolerance of SH₄₀ and Balenghaitang to iron-deficiency stress.

Key words: Iron-deficiency, Apple rootstocks, Root, Organic acid