Cytotaxonomy Studies On Large-flowered Chrysanthemum Varieties

Chrysanthemum varieties has an abundant variation among different varieties and there are a lot of controversy about the classification of varieties especially the large-flowered chrysanthemum varieties which hadn't a uniform classification standard. All thease problems bring many difficulties to the identify of varieties. Cytotaxonomy is a simple and useful method to supplies the basic genetic parameters on chromosome level, so the karyotype analysis of plants is valuable for the studies of their evolvement. The cytotaxonomy studies on large-flowered chrysanthemum varieties is significant in practice and theory. The previous research suggests that the karyotypes are various among different varieties. This research, based on achievement before, analyse the karyotypes of 58 large-flowered chrysanthemum varieties to supply evidence for the classification of varieties.The main resulits are:1.Set up an effective root-tip squashing method. The root-tip of two selected representative large-flowered Chrysanthemum varieties were obtained in different time, treated with different kinds of pretreatment agent, different temperature and hour and different dissociating time, and observe the number of the mitosis metaphase cells, the degree of treatment complications and the fact that chromosomes are distinct and countable. The conclusion is:Pretreating roots of 1cm with the saturated p-dichlorobenzene for 4 hours at 4℃, fixing them with Carnoy's for 22-24 hours and dissociating with 1mol/L HC1 at 60℃for 10min. This way can obtain slides of metaphase chromosomes with a high quality and quatity.2.By Root-tip squashing method, the metaphase chromosome numbers and shapes of 58 large-flowered chrysanthemum varieties are observed to ananlyse their karyotype parameters,The conclusions are:(1)The chromosome number of 58 Large-flowered Chrysanthemum varieties are among 46-72. Most of these 58 Large-flowered Chrysanthemum varieties are hexaploids and hexaploids'aneuploids, and the rest are octploids, septuploids, pentaploids and their aneuploids.(2)Chromosome satellites were obviously observed in 40.7% of these 58 varieties, with the most chromosome satellites is 4, and all of these chromosome satellites are on the end of short arms.(3)The karyotypes of the most varieties are 2B with some 2A or 2C. The numbers of 4 kinds of chromosomes are:m>sm>M and st. (4)The means of the ratios of long arm and short arm and the relative length of chromosomes are more different among 58 varieties, and there are less difference on the asymmetry coefficient of karyotypes. The correlation between the means and ariations of the ratios of long arm and short arm vary is significant.3.Compare karyotype parameters among large-flowered chrysanthemum varieties of different petal types, petal colors as well as chinese varieties and japanese varieties and the conclusions are:(1)Compare the karyotypes of varieties of different petal types and the results suggest:the evolve process of petal types that from flat to spoon to Qiuled to anemone, the number of octploids, septuploids, pentaploids and their aneuploids is less and less as well as the number of hexaploids and hexaploids 'aneuploids is more and more., and the diversity of the means of the ratios of long arm and short arm becomes obvious within varieties of the same petal type. Varieties of anemone petal show mere diversity than varieties of other petal types on the means of the ratios of long arm and short arm, the relative length of chromosomes, the ariations of the ratios of long arm and short arm and the asymmetry coefficient of karyotypes.(2)Varieties of different colors show less diversity than varieties of different petal types on these karyotype parameters.(3)The range of karyotype parameters of Japanese varieties is within that of Chinese varieties.4.Q cluster analysis of these 58 Large-flowered Chrysanthemum varieties'karyotype parameters suggests:Japanese varieties doesn't cluster alone, and varieties of spoon petal and anemore petal don't clust alone either and they cluster with varieties of flat petal and spoon petal respectively. Varieties of flat petal and spoon petal as well as varieties of similar flower types cluster alone respectively. Varieties clusterring together share some similar characters on flower shape.5.Correlation analysis of morphological characters and karyotype parameters of 44 Large-flowered Chrysanthemum varieties suggests that:more morphological characters have a high correlation with the chromosome number;and the morphological characters of flower shape and leaf shape have a high correlation with karyotype parameters.All the conclusions suggest that,karyotype parameters show a obvious diversity among different Large-flowered Chrysanthemum varieties.Depends on Cytological Study, dividing Large-flowered Chrysanthemum varieties with petal types is reasonable in some sense, but the detailed dividing standard may be analysed carefully to be more satisfying.