In order to know the effects of excess boron supply on different apple cultivars, this experiment was conducted with 4-year-old apple trees (Dlalus domestica Borkh) on M.26 rootstock by supplying different concentration of boron in sand culture solution.
The results were as follows:
Boron toxicity symptoms occurred in leaves, fruits and branches, in high concentration treatments of boron.
Toxicity symptoms of leaves were characterized by yellowing of midrib, large lateral vein and their neighboring tissue or backward bending of leaves and fading of green color depending on cultivars. Toxicity symptoms of leaves occurred most severely in Fuji, mildly in EarliBlaze cultivar.
Toxicity symptoms of fruits were characterized by internal browning of flesh which is very similar with the internal browning of Fuji apple occurring after long term storage. This disorder was most severe in Fuji, Mutsu and EarliBlaze, but very mild in Starkrimson.
Fruits produced in high boron treatments showed an accelartion of red color development, and an increase in fruit firmness and soluble solids content, but a decrease in acid content of fruit. Toxicity symptoms of branch showed a canker-like appearance on some parts of branch bark and on bark of graft union area. This disorder was most severe in Starkrimson and Fuji, but mild in EarliBlaze cultivar.
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