To investigate whether reproductive disorders exist in the sexual reproduction of Ziziphus jujuba Mill. ‘Zhongqiusucui’ and to understand the reproductive biology of ‘Zhongqiusucui’ and genetic improvements in jujube trees, we used ‘Zhongqiusucui’ flowers at different developmental stages as materials and conducted field and microscopic observations on the developmental pattern of mega- and microsporogenesis, as well as on the development of male and female gametophytes. The results show the following. 1) From the inflorescence development stage to flowering, the grade 0 bud on the inflorescence exhibited an increase in horizontal diameter, longitudinal diameter, peduncle length, and bud weight, but the rates of increase were different. From day 1 to day 5 after the inflorescence had developed, floral buds mostly grew horizontally. Day 5 was the floral bud flattening stage. From day 6 to day 8 after the inflorescence had developed, floral buds mostly grew longitudinally, and day 8 was the floral bud enlarging stage. 2) The stamens of ‘Zhongqiusucui’ had five anthers, and there were four locules per anther. The anther wall consisted of epidermis, endothecium, one- to two-layered middle layer, and a secretory-type tapetum. In addition, the development of the anther wall belonged to the basic type. The cytokinesis of the microsporocytes was synchronous, the tetrads mostly arranged as a tetrahedron, and the mature pollen had three germ pores, three grooves, and was bicellular pollen. During meiosis, the microsporocytes in each locule were at the same phase and therefore exhibited synchrony. Among the different anthers in the same floral bud, as well as the four locules in the same anther, the microsporocytes had asynchronous meiosis. 3) The pistils in the ‘Zhongqiusucui’ had two ovaries, two anatropous ovules, inner and outer integument, crassinucellate tetrads formed by the meiosis of megasporocytes aligned linearly along the nucellus, megaspore at the chalazal end that developed into the functional megaspore, which underwent mitotic division three times and developed into the mature embryo sac containing seven cells and eight nuclei, and embryo sac development of the Polygonum type. 4) The external morphology of the ‘Zhongqiusucui’ floral buds correlated with the internal developmental stage of the male and female gametophyte. Therefore, the internal developmental progress of the stamen and pistil can be determined by the external morphological characteristics of the floral buds.
To explore the reasons for seed abortion in southern China fresh-eating jujube, improve its reproductive biology, and provide a theoretical basis for the crossbreeding of jujube, we carried out self-pollination and cross-pollination experiments with Ziziphus jujuba Mill. ‘Zhongqiusucui’ as the female parent. We observed the process of pollen tube growth in pistil and embryo development by fluorescence microscopy and paraffin section methods. The results show there were self- and cross-incompatibilities during pollination and fertilization, and there were no significant differences in pollen germination and pollen tube growth between self-pollination and cross-pollination. It took at least 4 hours for pollen and stigma to recognize each other, 6 hours for pollen to germinate on the stigma, and 12 hours for the pollen tube to penetrate the mastoid cells of the stigma. After 48 hours of pollination, the pollen tube reached one third of the style. The pollen tube remained stagnant 72 to 120 hours after pollination, and remained at one third of the stylar canal. Simultaneously, the pollen tubes on the stigma twisted and interacted with each other, and expanded into a spherical shape. A few pollen tubes reached the ovary and completed fertilization. However, some early globular embryos degenerated before forming into globular embryos and resulted in the formation of empty embryo sacs, which leads to seed abortion. In conclusion, the poor pollination and fertilization, and the blocked development of the embryo resulted in seed abortion in Z. jujuba ‘Zhongqiusucui’.