Megasporogenesis, Microsporogenesis, Development Of Gametophytes And Florescence And Pollination Traits Of Annona

The flowers of Annona species are hermaphroditic and exhibit protogynous dichogamy, which force to pollinate flowers by hand for commercial production. This study was meant to explore microsporogenesis, megasporogenesis and development of the male and female gametophytes and blooming and pollination traits of Annona. In this paper, paraffin cut section method was used to observe the development of pistil and stamen of sugar apple、African Pride and Fenglishijia atemoya. Then we used African Pride and Fenglishijia atemoya as materials to observe the florescence traits, pollen morphology, pollen germination and pollen tube behavior on the stigma. Scanning electron microscope(SEM) was used for pollen morphology, pollen germination on the medium of BK was tested, pollen germination and pollen tube behavior after self- and cross-pollination were observed via fluorescence microscope and the fruit setting rate were also observed. The results are as follows:(1) The bud length of Annona correlated well with the development stage of male and female gametophytes; The process and tissue structures were the same for megaspore and microspore development of different varieties, but the corresponding morphology of buds were different.(2) The anther was tetrasporangiate, the development pattern of the anther wall was basic type, glandular tapetum, the type of cytokinesis during meiosis of microspore mother cell was continuous, microspore cell tetrad was obilateral, the mature pollen was aggregated as tetrad; The ovary had many chambers, each with 1 anatropous ovule, marginal placentation, the ovule was bitegmic and crassinucellate, megaspore is in the shape of line; development type of embryo sac is polygonum.(3) The flowers of Annona species were hermaphroditic, had hundreds apocarpous gynaccium and monadelphous, belonged to superior-hypogynous flower, short style, adnate anther, pollen was released in longitudinal split; The petals of Africa Proud was thicker than Fenglishijia atemoya, while the latter was longer in petals; Flowering phenology of Africa Proud was 5 days ealier than Fenglishijia atemoya; During the flowering phase, flowers presented three different stages:the petals started to crack (pistil was already mature and the stigma was able to accept pollens), half open (stigma still had the ability to accept pollens), fully open (pollen was released but stigma can not accept pollens), and the whole stage almost last 7days.(4) African Pride and Fenglishijia atemoya exhibited similar pollen morphology, presented a oval shape in equatorial view. For both cultivars, the shape of pollen was actinomorphy radial symmetry type, and the ornamentation of exine was cave-shaped, no germ pores were seen,1-2 ditches can be seen via equatorial views,4 ditches can be seen via polar views; Polar view of the former was suborbicular, the latter was nearly oval; As for surface, the former was smooth, but there are small particles on the latter.(5) The pollen germination rate varies at different flowering stages. And the early and end stage were significantly lower than fullbloom period; Sucrose concentration significantly effected pollen germination rate,0.06 g/L was the most appropriate; The adding of stamens to the medium can significantly improve the germination rate; Pollen was not resistant to storage, at 4℃, the pollen almost completely out of energy at 4th days.(6) After self-and cross-pollination of African Pride and Fenglishijia atemoya,there are indications that did not show significant differences, including seeds number in fruit、pollen germination rate on the stigma and seed weight. For all cross combinations, pollen tube reached the embryo sac within 12-24h and the fruit setting rate were high.