title: Cold Treatment Breaks Dormancy but Jeopardizes Flower Quality in Camellia japonica L.
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.
authors.affiliation: Institute for Sustainable Plant Protection, National Research Council Torino, Italy ; Department of Agricultural, Forest and Food Sciences, University of Torino Grugliasco, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Berruti
authors.affiliation: Department of Plant Production, Faculty of Bioscience Engineering, Ghent University Ghent, Belgium.
authors.forename: Annelies
authors.initials: A
authors.lastname: Christiaens
authors.affiliation: Plant Sciences Unit, Institute for Agricultural and Fisheries Research Melle, Belgium.
authors.forename: Ellen De
authors.initials: ED
authors.lastname: Keyser
authors.affiliation: Department of Plant Production, Faculty of Bioscience Engineering, Ghent University Ghent, Belgium.
authors.forename: Marie-Christine Van
authors.initials: MC
authors.lastname: Labeke
authors.affiliation: Department of Agricultural, Forest and Food Sciences, University of Torino Grugliasco, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Scariot
keywords: RT-qPCR; abscisic acid; anthocyanin; chilling requirement; dormancy breaking