|Authors: ||A. Sønsteby, O.M. Heide|
|Keywords: ||black currant, chilling, dormancy, flowering, growth cessation, photoperiod, Ribes nigrum, temperature|
Black currant is a woody plant in which growth and development are intimately controlled by, and synchronised with seasonal changes in photoperiod and temperature.
Concern over the potential impact of global warming on plant phenology and yield, led us to initiate relations.
An experimental system with single-stemmed potted plants was developed which allowed a research program to address both qualitative and quantitative assessment of climatic responses.
Growth cessation and flowering were both induced by short days, with critical photoperiods of approximately 17 and 16 h, respectively, for most cultivars.
Both processes were advanced and promoted by increasing autumn temperature with an optimum in the 18-21°C region.
An exception was cultivars of high-boreal origin, which had an early growth cessation at low temperature.
Unexpectedly, however, not all plants flowered after exposure to 10 h photoperiod, and the number of flowers decreased as the photoperiod was reduced from the near-critical length of 15 h.
This was due to premature dormancy induced by an abrupt change to photoperiods well below the critical level.
Field experiments revealed that cultivars of varying geographic origin, exhibited a typical latitudinal cline in their photoperiodically controlled timing of growth and flowering responses.
Breaking of bud dormancy and promotion of flower bud development required chilling at -5°C for 14 weeks or more for optimal responses.
However, while chilling at -10°C for 8 weeks resulted in dormancy release, continued chilling to 16 weeks inhibited bud break completely.
We therefore propose that excessive chilling induces secondary bud dormancy in black currant.
The observed high chilling requirements of black currants concur with the reported vulnerability of this crop to declining winter chill in the wake of the ongoing global warming.
Furthermore, such conditions also induce a particularly deep bud dormancy state that further increases the chilling need.
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