Influence of bicarbonate salts, used against apple scab, on selected primary and secondary metabolites in apple fruit and leaves

In a field experiment, the effectiveness and phytotoxicity of inorganic fungicides such as potassium bicarbonate (PBC) and sodium bicarbonate (SBC) were compared with water applications for the control and fungicide treatments as a classical method for controlling scab infections in cultivar ‘Braeburn’. To examine all possible effects of this inorganic fungicide disease severity, external quality parameters (mass, firmness, colour), and the content of primary and secondary metabolites were measured and recorded on fruit; and disease severity, the content of secondary metabolites and accumulation of potassium were monitored in apple leaves. The results indicate that both inorganic fungicides are effective against apple scab and do not cause any phytotoxicity at given application doses. External fruit quality parameters were comparable with fruit produced with fungicide treatments. Similarly, the PBC treatments exhibited a positive effect on higher content of sugars and organic acids in comparison to fungicide treatments. No significant differences between fungicide and PBC or SBC treatments were observed in the content of analysed phenolic compounds. The content of phenolic compounds in leaves, were comparable to those in fungicide treated trees. However, this only indicates the activity of defence mechanisms in apple leaves. The use of PBC also positively affected the potassium accumulation in leaves through the growing season. Given that these products are not toxic to human health, PBC and SBC can potentially present a perspective protection in the apple orchards especially for the control of apple scab in organic fruit growing.

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► SBC or PBC used at 1% concentration were effective in controlling apple scab.
► PBC positively affected potassium accumulation in leaves.
► Bicarbonate salts potentially influence plant secondary metabolism.
► PBC treatments have a positive effect on fruit quality parameters.
► PBC enhanced sugar and organic acids accumulation in the mature fruit.