Changes in the morphology of the bud meristem and the levels of endogenous hormones after low temperature treatment of different Phalaenopsis cultivars

Abstract Phalaenopsis (Orchidaceae) is one of the most popular and trendy potted plants in the world. In order to achieve a better understanding of the influence of cold treatment to flowering, the morphological and hormonal changes were determined in three Phalaenopsis cultivars during flower bud differentiation and development. It was found that the three cultivars were all coordinated by the cold-induced release of reproductive bud dormancy, which was vernalisation pathway. The morphological development of flower bud differentiation was similar in Phalaenopsis cultivars: flower organ differentiation began with the formation of the outer petal primordia, followed by the inner petal primordia and finally, by the lip and column (stamen and carpel) primordia. The earlier the flower bud started differentiation, the earlier the flower bloomed. The timing of inflorescence primordium differentiation and flower bud development was controlled by plant hormones. It was found that ABA and GA3 levels of apical meristems of stalk before flower bud differentiation was high. High levels of IAA and ZR controlled the vegetative growth phase and the floral inductive phase, like the elongation of stalk.