Abstract
Bud dormancy is an important developmental stage that ensures that trees can tolerate environmental stresses in winter and bloom uniformly in the following spring. Regarding Rosaceae floral buds, exposure to chilling conditions promotes floral primordium development and the transition from endodormancy to ecodormancy. A subsequent period of warm conditions induces blooming. In Japanese apricot (Prunus mume), dormancy progression is accompanied by morphological changes that alter the bud appearance and internal structures. We used a modified BBCH scale and conducted microscopy analyses to elucidate the bud developmental stage of three cultivars with contrasting chilling requirements. The floral bud developmental period corresponding to BBCH stages 51–53 includes the transition from endodormancy to ecodormancy in all three cultivars. Male meiosis and microspore development occurred during this transition in high-chill cultivars, but were detected considerably later than the transition in the low-chill cultivar. A slow or suspended developmental phase was observed only for the high-chill cultivars upon completion of floral primordium organ differentiation, suggesting that chilling may be required to induce floral bud maturation and dormancy release only in high-chill cultivars. Possible relationships among BBCH stages, flowering-related morphological characteristics, and the dormancy phase transition in Japanese apricot are discussed.
Highlights
Exposure to low temperatures affects floral development in numerous species
The high-chill cultivars had a constant relative growth rate (RGR) from November onward, whereas the RGR of the low-chill cultivar increased substantially in December. These results suggest that floral bud growth ceased in October, but resumed somewhat from November onward as dormancy progressed in all three cultivars
New classifications and terminologies to describe plant dormancy at the cellular level were recently proposed by Considine and Considine (2016) [38]
Summary
Exposure to low temperatures affects floral development in numerous species. It is considered that the chilling treatment that promotes floral primordium development and maturation is necessary for the subsequent blooming and fruiting process [2]. Bud dormancy refers to the state in which the bud meristem is unable to resume growth and development under suitable environmental conditions [3]. Bud growth ceases because of internal factors, and a particular period of low temperatures is required for buds to regain the competency to grow. A subsequent exposure to a certain period of warm conditions is required to release buds from ecodormancy so they may enter the full bloom stage. If the floral buds of Rosaceae species, including Japanese apricot (Prunus mume), are not sufficiently exposed to low temperatures, they will be unable to develop
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