Sexual Differences And Reproductive Strategy Of Hemarthria Compressa (L. F.) Between Different Ploidy

Hemarthria compressa (L. f.) R. Br., a stoloniferous perennial C4grass, belongs to the tribe Andropogoneae, family Poaceae, which mainly distributed in tropical or subtropical regions. Owing to its high yield, regeneration ability, strong resistance, convenient management, it is widely used in the grassland animal husbandry production and ecological environment construction of Changjiang River rasin and coastal provinces. As a typical warm season grass, H. compressa has strong ability of vegetative propagation with strong rhizomes and stolons, but its sexual reproductive ability is poor, no seed under the wild or cultivated environments. The stolon cuttings were usually used in the fields, which take more time and money. So the lack of seed to a great extent limit the application and popularization of whipgrass. Due to the limitation of sexual reproductive ability, three H. compressa cultivars have been generated by the selection of clones in breeding, which makes genetic basis relatively single and further breeding work hardly achievable. For the sake of improving the seed setting rate to meet the practical need and break the existing pattern of cultivating, the studies on reproductive characteristics of whipgrass have been conducted, but the conclusions are very different from previous studies, which are not comprehensive and lack basic cytologic research.In this study, according to H. compressa germplasms chromosome ploidy basis, to investigate the relationship between the different times of spike differentiation and the external form, the environment from the level of the individual, to identify pollen germination and the double fertilization of reproductive disorder. At the population level, to explore the different times of population growth and changes of reproductive allocation. Through the analysis of clonal diversity and identification of clonal structure, reveal the reproductive strategy, revealing the H. compressa in natural populations of key rate is low and its influence to solve the actual production needs, and lay the theoretical foundation. The main conclusions are as follows:1. The40samples of H.compressa, included7samples of tetraploids (H014, H026, H028, H029, H052, H053, WG02) and33hexaploids, chromosome number is n=9.No correlation between chromosome aneuploidy variation ratio and seed setting rate is not significant. Natural seed setting rate of hexaploids are low, but higher for tetraploids. Find4materials with strong seed productive potential, that is H028, H029, H052, H053.2. H. compressa spike differentiation is a continuous process, divided into primary stage, elongation stage, nodular stage, spikelet, floret differentiation stage and booting stage,6stages. Fully expanded leaves can be used as one of the morphological index of vegetative growth to reproductive growth judgment. Fully expanded leaf number greater than12, the vegetative growth to reproductive growth changed gradually. The first mature leaves first stem to stem tip distance negatively associated with the differentiation of young spike. Appropriate temperature promote effective means of spike differentiation, when≥10℃accumulated temperature over1400℃, H. compressa began to spike differentiation.3. There is no reproductive barriers in the H. compressa development process of megasporogenesis and female gametophyte. Tetraploid material meiosis process was almost normal, abnormal cells was3.41%. Hexaploid abnormal rate was22.58%, mainly abnormal will happened in late of meiosis Ⅱ cytokinesis is not synchronized. Tapetum cells in meiosis of microspore mother cell division period ahead of degradation or disintegration, accounting for about15%of all. Hexaploid pollen tube germination, the pollen tube coiled round the style instead of into the papillary cells; Tetraploid materials pollen can successfully inserted into the ovary and the release of sperm cells to complete the double fertilization. It will take20h to finish double fertilization of H. compressa. After bloom4-5hours pollen tube entered the synergids and released sperm,5-10h sperm went to the egg;6-12h later, sperm attached to the egg nuclear envelope The sperm and egg nucleus mixed together and formed the primary endosperm were happened14-20h after bloom.4. There are remarkable differences in reproductive allocation of biomass between different ploidy of H. compressa,6.6±0.9%and2.2±1.3%, respectively. Nitrogen, phosphorus, calcium and boron has a positive role in development and seedformed of H. compressa. Calcium and boron content in plant is low. It is the limit factor of sexual reproduction. Stand conditions, hexaploid populations tend to asexual reproduction, tetraploid populations tend to sexual reproduction. 5. Clonal diversity and clonal structure in small scale of hexaploid H. compressa populations were studied by ISSR techniques. There were four different genotypes in the population, the average clone size (NC) was31.5, the ratio of different genotypes was0.032; evenness of the distribution of genotypes was0.581; the mean Simpson’s index was0.459. In certain extent, plant populations are produced by a few genotypes in a asexual way.In summary, H. compressa population reproductive strategies to give priority to asexual reproductive, but do not give up sexual reproduction. Sexual reproduction in tetraploid plants appear normal, and can form numbers of seeds, spraying micronutrient fertilizer is an exploring ways to raise seed setting. Hexaploid plant has a certain ability to sexual reproduction, but want to improve the seed setting rate, need more hexaploid germplasm resources of chromosome genetic constitution, fertilization and so on in-depth analysis.