Abstract
Camellia japonica L. is an evergreen shrub whose cultivars are of great ornamental value. In autumn, after flower bud differentiation, dormancy is initiated. As in many other spring flowering woody ornamentals, winter low temperatures promote dormancy release of both flower and vegetative buds. However, warm spells during late autumn and winter can lead to unfulfilled chilling requirements leading to erratic and delayed flowering. We hypothesized that storing plants at no light and low temperature could favor dormancy breaking and lead to early and synchronized flowering in response to forcing conditions in C. japonica ‘Nuccio’s Pearl’. Plants with fully developed floral primordia were stored at dark, 7°C, and RH > 90% for up to 8 weeks. To monitor endodormancy release during the storage, we evaluated the content of abscisic acid (ABA) in flower buds and the expression profiles of five putative genes related to dormancy and cold acclimation metabolism in leaves and flower buds. In addition, the expression of four anthocyanin biosynthesis pathway genes was profiled in flower buds to assess the effect of the treatment on flower pigment biosynthesis. At 0, 4, 6, and 8 weeks of cold treatment, 10 plants were transferred to the greenhouse and forced to flower. Forced plant flower qualities and growth were observed. The ABA content and the expression profiles of two dormancy-related genes (CjARP and CjDEH) suggested that dormancy breaking occurred after 6–8 weeks of cold treatment. Overall, plants treated for 6–8 weeks showed earlier vegetative sprouting, enhanced, and homogeneous flowering with reduced forcing time. Prolonged cold treatments also reduced flower size and longevity, anthocyanin content, and pigment biosynthesis-related gene transcripts. In conclusion, the cold treatment had a promotive effect on dormancy breaking but caused severe drawbacks on flower quality.
Highlights
Camellia japonica L. (Theales, Theaceae) is an acidophilic evergreen shrub whose more than 3,000 cultivars (Mondal, 2011) are of great ornamental value
We focused our attention on how controlled cold treatments could promote early and synchronized flowering and normal regrowth in dormant C. japonica ‘Nuccio’s Pearl’
To monitor endodormancy release during the treatment, we evaluated the content of abscisic acid (ABA) in flower buds and the expression profiles of five putative genes related to dormancy and cold acclimation metabolism (CjSuSy, CjERF, CjDEH, CjCAP, and CjARP) in leaves and flower buds
Summary
Camellia japonica L. (Theales, Theaceae) is an acidophilic evergreen shrub whose more than 3,000 cultivars (Mondal, 2011) are of great ornamental value. The release of flower bud dormancy is generally stimulated by extended periods at low temperatures This is the case of genera phylogenetically close to Camellia, such as Rhododendron (Bodson, 1989; Christiaens et al, 2015) and Hydrangea (Anderson et al, 2009), where the exposure of floral buds to cold temperatures (between 2 and 7◦C) stimulates endodormancy release and initiates normal growth and anthesis during the following spring (Arora et al, 2003). To monitor endodormancy release during the treatment, we evaluated the content of ABA in flower buds and the expression profiles of five putative genes related to dormancy and cold acclimation metabolism (CjSuSy, CjERF, CjDEH, CjCAP, and CjARP) in leaves and flower buds. Plants were forced to flower in the greenhouse and morphological characteristics were determined
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