Anatomy and morphology of flower bud differentiation of Pouteria caimito Radlk

Abstract: 【Objective】The study aimed to explore the anatomical structure changes during flower bud differentiation and provide a theoretical basis for flowering regulation technology and then improve the production technology of Pouteria caimito Radlk.【Methods】Pouteria caimito Radlk planted in the Resource Collection of Zhangzhou Institute of Agricultural Sciences was used as the research material.The experimental observation and sampling were carried out in early March, 2021 to investigate the phenological stages of flower bud differentiation and development. Samplings were carried out every 5 days from the beginning of flower bud differentiation. Each time, the flower buds of Pouteria caimito Radlk with the same size and the same development period from the plants in 20 pots were randomly se-lected. The collected flower buds were put into a centrifuge tube and fixed with FAA fixative. The tis-sue morphology and structure of the flower bud differentiation were observed by paraffin section method.【Results】The differentiation of the various structures of the flower buds of Pouteria caimito Radlk was a continuous process. According to the typical structural characteristics of the formation and differ-entiation of floral organs during the differentiation process, the whole differentiation process was divided into early stage of differentiation phase, sepal differentiation phase, petal differentiation phase, pistil and stamen differentiation phase, ovary expansion phase, and pistil and stamen maturity phase. April 1st to 6th was the initial stage of flower bud differentiation of Pouteria caimito Radlk. At this time, 55% of the flower buds had entered the early stage of differentiation. The meristem at the growth point of the bud body splited faster, and the top was conical. April 6th to 11th was the sepal differentiation phase,during the period, 45% of the flower buds of Pouteria caimito Radlk had entered this phase. Because the inner and outer cell division speeds of the flower buds were different, protrusions were formed around the flower buds to form the calyx primordium. April 11th to16th was the petal differentiation phase, and 70% the flower buds had entered this phase. On the inner side of the calyx primordium, new protrusions appeared at the edge of the flower primordium to form the petal primordium. April 16th to 21th was the pistil and stamen differentiation phase, and 65% of the flower buds were found to enter this phase. The inner petal primordium continued to grow and develop, the sepals and petals gradually elongated, and the growth point continued to widen, and several small bulges were differentiated inside the petal primordium, thus forming the stamen primordium, and at the same time, the flower bud body differentiated in the middle position. A new bulge, the pistil primordium was formed. April 21th to 26th was the ovary expansion phase, at this time 70% of the flower buds have entered this phase, and the lower part of the pistil primordium gradually expanded to form an ovary. The ovule primordium ap-peared inside the bud, and the growth was accelerated at the same time, and the top formed a clear protrusion. April 26th to May 1st was the pistil and stamen maturity phase. More than 90% of the flower buds have entered this phase. The ovary continued to expand into a gourd-like shape. There were 1-2 ovules in the ovary and all anthers had formed. The differentiation of flower bud morphology had com- pleted, and the various organs of Pouteria caimito Radlk flower gradually matured.【Conclusion】The flower bud differentiation process of Pouteria caimito Radlk could be divided into six stages: early phase of differentiation, sepal differentiation phase, petal differentiation phase, pistil and stamen differentiation phase, ovary expansion phase, pistil and stamen maturity phase. The flower bud differentiation process of Pouteria caimito Radlk showed obvious“slow-fast”trend. The differentiation started from early April to the end of May. The duration was short, the differentiation speed was fast, and the differ- entiation process time was relatively concentrated. There was an overlap in each period of the morpho-logical differentiation of flower buds.