Pollen morphology observation and palynological studies of Diospyros

Abstract:【Objective】Diospyros belongs to persimmon family. China has a long history of persimmon cultivation and a rich germplasm resource with 1 058 varieties distributed throughout the country. Because of its nutrient-rich fruit, persimmons are popular. They are also beautiful ornamental trees because of their graceful appearance, beautiful foliage and colorful fruit. The pollen morphology is relatively stable and thus an important criterion for plant classification. With the use of scanning electron microscopy, palynological study has entered a new stage. In this study, experiments were conducted to explore the possibility of distinguishing the species and cultivars of Diospyros based on palynological characters and exploring their phylogenetic relationships with cluster analysis.【Methods】A total of 21 materials including seven Diospyros species and eleven cultivars of D. kaki and pomegranate flowers, dicranostigma, corn poppy and Campsis grandiflora flowers were used as the materials. At anthesis, morphology of the pollen surface was observed under scanning electron microscopy (SEM) . All the above persimmon materials were collected from the National Field Genebank For Persimmon and the rest materials from the campus of Northwest A & F University. Pollen morphology of Diospyros wascharacterized by six quantitative traits including poleaxis length (P) , equatorial width (E) , stripe length, stripe width, germination length and germination pore size. The data were subject to statistical analysis and cluster analysis.【Results】Firstly, unlike pomegranate flowers, dicranostigma, corn poppy and Campsis grandiflora, the exine ornamentation of Diospyros was grain fringe, which is significantly different among them. The exine ornamentation of the corn poppy pollen was raised in a hilly shape; the pollen of Campsis grandiflora had a network structure; that of pomegranate was with tumor-like protuberances; dicranostigma had both tumor-like protrusions and a network structure. Secondly, the pollens of the six persimmon species could be distinguished by their ornamentals. D. glaucifolia pollen fringes formed a short clusters in helical arrangement; D. oleifera pollen had stripes that were often accompanied by a'V'-type cross arrangement; the stripes D. lotus pollen were long worm-like with irregular arrangement. Pollen surface of D. spp. was with granule protuberances and knitting lines. The fringe D.virginiana pollen was in a rugged, undulated arrangement; and D. cathayensis pollen stripes were clustered together with perforations. Thirdly, there were also significant differences in pollen external morphology among the other eleven cultivars of D. kaki. For example, the fringe of'Xiangyangniuxinshi'was the widest, reaching 97.35 μm, and there was a perforation. But the fringe of'Panxianshuishi'was only 0.85 μm. Unlike'Xiangyang niuxinshi''Touh achi'had no perforation on the pollen surface, and its surface was relatively smooth with longer stripes. Besides, the pollen grains at flower bud stage were generally larger than those at full-bloom, and the stripes were wider. Furthermore, at full-bloom stage, pollen exine stripes of D. kaki were relatively dry and sparse, but at bud stage they were relatively plump and tight. Moreover, 'Huazhongxiongzhu''Xiangyang niuxinshi'' Zenjimaru'and'Taiwanzhengshi'produced huge pollens. Giant pollen size was about 1.9 times the size of the normal pollen, accounting for 23.5% on average in the materials observed in this experiment. Cluster analysis of the 17 species of persimmon using UPGMA divided them into five categories and showed their genetic relationships.【Conclusion】The exine ornamentation of the pollen of Diospyros is significantly different from that of the four non-persimmon plants, and it is specific and stable. According to the pollen external morphology, we can determine whether the pollen belongs to Diospyros. Although the exine ornamentation is generally similar among Diospyros species, there are some differences in exine ornamentation, pollen size and shape, etc.. These differences can use not only for distinction of the six Diospyros species but also for distinction the 11 cultivars of D. kaki. Due to the different time of pollen collection, the pollen morphology may be different, and therefore the results obtained in this paper may have limitations in the application. In addition, the existence of giant pollen (2 n gametes) has been found in'Zenjimaru'and'Taiwanzhengshi', indicating that huge pollen is not ubiquitous but only presents in some varieties of D. kaki. Cluster analysis showed the close relationship between the 17 species of persimmon plants. The results show that palynology provides a reliable reference for classifying Diospyros.