Lateral Bud Dormancy in the Blackcurrant Ribes nigrum (L.)

Previous investigations have shown that the inhibition of lateral buds in blackcurrants soon after their formation is due to apical dominance and this is followed by leaf inhibition. The present studies have revealed that bud scales are the main cause of inhibition even before leaf fall. The inhibitor level assayed by the wheat coleoptile test shows large seasonal changes; it is maximal in early autumn and minimal in spring. Inhibitor levels are reduced by low-temperature treatment in parallel with the promotion of dormancy breaking; temperatures well below freezing, applied for very short times, almost certainly act through the killing of bud scales in the same way as does rapid high-temperature treatment. Other treatments causing bud break in the presence of high inhibitor levels are: continuous illumination, ethylene vapour, and application of gibberellic acid. It is suggested that bud inhibition in the blackcurrant is due to the formation of an inhibitor produced by the leaves and accumulated in the bud scales. The inhibitor (probably abscisic acid) may then interact with internal gibberellin levels, summer and winter dormancy differing only quantitatively.