Average daily temperature controls floral bud formation rate, callose deposition and flower development of Hydrangea macrophylla 'Early Blue'.

Hydrangea macrophylla 'Early Blue' was exposed to six different day (DT) and night (NT) and average daily temperatures (ADT) during flower bud formation (DT/NT°C: 12/12, 17/12, 17/17, 22/12, 22/17, 22/22). The aim was to evaluate the effect of ADT and DT/NT on the rate of bud formation and forcing time after a period of chilling. Furthermore, the role of callose in dormancy induction and release during cold storage was investigated. ADT ≤ 17°C accelerated flower bud formation irrespective of DT and NT compared to an ADT > 17°C. Floral buds developed at ADT 17°C contained significantly lower level of callose compared to buds from the higher ADT regimes (ADT >17°C). After 6 weeks of chilling (10°C) the callose level was decreased to a similar level irrespective of the DT/NT regime during floral bud formation and/or floral stage at the start of the chilling treatment. We conclude that callose may play an important role in the dormancy release of H. macrophylla. However, floral buds do not have to be fully developed to remove the callose in response to chilling and no clear relationship was found between the levels of callose after chilling and forcing time. [ABSTRACT FROM AUTHOR]