Study On Reproductive Biology Of Caryopteris Mongolica Bunge

Caryopteris mongolica Bunge is a type of subshrubs belonging to Verbenaceae, Caryopteris. It is mainly found in provinces of Hebei, Shanxi, Shanxi, Inner Mongolia, Gansu in China and some areas in Mongolia. C. mongolica is able to survive under severe environmental conditions; therefore, it has been widely planted for soil and water conservation in arid and semi-arid regions. C. mongolica is also used for purposes of gardening and Chinese medicine. In this thesis, reproductive biology of C. mongolica was studied, as the first time, in details by using artificial populations and natural populations. The research focuses on embryology, flowering phenology, breeding system, pollination biology, patterns of fruit and seed set, seeds germination, and karyotype analysis. Main conclusions are presented as follows.1. It was observed that the anther of C. mongolica has 4 microsporangiums. The wall of a mature anther is composed of epidermis, endothecium (1 layer), middle layer (1 layer) and glandular tapetum (1 layer). Its development follows the dicotyledonous type. Cytokinesis are carried on simultaneously by microspore mother cells meiosis. Tetrads are mostly tetrahedral, but occasionally isobilateral. The mature pollen grain is a two-celled type with three colpates. After the microspore tetrad is formed, some forms of the microspore are under developed, and lose protoplasm. Therefore, sterile pollens are about 4.74% of the mature pollen grains.C. mongolica has 2 carpels in pistil, and 4 locules in ovary. Each locule has 1 ovule, and axile placenta. The ovule is anatropous, unintegmic, and tenuinucellatae. The megaspore tetrads are linear and the chalazal megaspore is functional. The embryo sacs consists of 7 cells with 8 nucleus, and belongs to Polygonum type. The differentiation and development of integumentary tapetum are accomplished during the megaspore tetrads stage. The disintegration comes before the formation of globular embryo.The embryo development is of the onagrad type. The erect mature embryo consists of cotyledon, germ, hypocotyl and radicle. The development of endosperm is a nuclear type and the primary endosperm nucleus divides earlier than the zygote. Mature seeds are exendospermous.2. There are significant differences in flowering phenology of C. mongolica between aretificial and natural populations. The dates of flowering phenology are also different in the same population in different years, but the flowering processes are in similar model of"Mass-flowering pattern". The synchronous index of both populations are more than 0.80. Most flowers opened before 10:00AM in sunny days and delayed or non-flowering in cloudy or rainy days.3. Flowers of C. mongolica are fragrant and nectariferous. Petals are in blue purple color. Such floral characteristics could attract insects. The stigma and anthers are not at the same height and separate in space during the flowering process, while both of them matured simultanousely. The pollen vigor and the stigma viability are temporally overlapped to a great degree. The values of P/O, OCI and bagging tests indicated that there is no apomixes in C. mongolica; the breeding system of the species is mixed with self-compatible and outcrossing; and the pollinators are required during the pollination process.4. The results of gravity slide experiment showed that the wind pollination is in a short distance and the outcrossing of wind pollination can be ignored. During flowering process, average amounts of nectar secretion follow the normal distribution. The average nectar secretion reached 1.44±0.43μl after flowered for 10h. Maximium nectar secretion was observed in the first day of blooming, and gradually decreased afterwards.Pollinators of C. mongolica include bees, flies and butterflies. One species of Amegilla, one of Bombus and Eristalis tenax Linnaeus were observed as main pollinators. Because of influences of pollination competitors and climatic and environmental factors, the pollinator visiting frequencies were always lower than 15 insect times/ inflorescence/h, which result in limited pollinators and pollen deficiency. These limiting factors have great influence on the reproductive success and probably make the flowers produce"few fruits".5. There are certain degrees of differences in seed setting of C. mongolica in different populations. All of the seed setting percentage, seed size and thousand-seed weight of the artificial populations are higher than the natural one. However, the seed set rates of different populations exhibited the same regulation on branches, manifested as the middle part>basal part>top part, while the seed size and thousand-seed weight in different populations manifested as the basal part>middle part>top part. The number of abortive seeds in single fruit of the artificial populations is significantly less than that of the natural populations.The percentage of abortive nutlets increases from the intermediate part to the edges in a single infructescence. The arrangement of seeds in single fruit is nonlinear and the numbers and positions of abortive seeds are uncertain.6. The seeds of C. mongolica germinate in a short period under optimum temperature and humidity, usually within 7-8 days. The seed germination rates of C. mongolica were found more than 90% in both artificial and natural populations in the current year.When kept at 4℃, the seeds vigor are higher than those kept in indoors and outdoors. The optimum temperature for seed germination is 20-25℃and the optimum soil water content is 7-20%. A layer of 2-5mm covering soil leads to the best of seed germination.The seeds of C. mongolica have resistant ability to heat and drought stress, but their vigor are greatly reduced under high temperature (40-45℃) and high humidity (100% relative humidity).7. The study results indicated that C. mongolica has chromosome number of 2n=26 and base number of x=13. The index relative length (I.R.L.) is 6L+6M2+8M1+6S. The karyogram fits well to the formula of 2n=2x=26=22m+4sm, and the karyotype belongs to the type of"2B". Its karyotype asymmetry index As.K% is equal to 58.48. Secondary constriction and satellite were not found.