Cytogenetical Studies On Some Chrysanthemum Cultivars

Chrysanthemum (Dendranthema×grandiflorum) is rather rich in diverse cultivars andinterspecific variation are quite common. Karyomorphology was studied via conventionalpressed slice method in 66 chrysanthemum cultivars which differ in flower diameter anduse. 63 cultivars of ornamental chrysanthemum including chrysanthemum with smallinflorescences (17 cultivars), cut chrysanthemum (14 cultivars) and potted chrysanthemumwith large inflorescence (32 cultivars), and 3 cultivars of edible chrysanthemum wereincluded in this study. The meiotic behaviors during pollen mother cell (PMC) developmentof 2 edible chrysanthemum cultivars which has invariable chromosome number was alsoobserved. In addition, the classification and evolution trends in different forms ofchrysanthemum cultivars were evaluated at the cytogenetical level. The main results are asfollowing:1. Ornamental chrysanthemum(1) The interphase nuclei and prophase chromosomes of all cultivars were found to beof the complex chromocenter type and the interstitial type, respectively.(2) The numbers of somatic chromosome rang from 48 to 62. Except that 'Hongxia'and 'Hongyigoupan' were haxaploid, 'Xiongshi' and 'Gujingou' were aneuploid (2n=55),the remaining cultivars were mixoploid, The ubiquitous mixoploidy phenomena indicatedthat genetic background was rather complex in chrysanthemum. The most frequency ofoccurrence of the distribution in chromosome numbers was 54 for different cultivars.Variation range in chromosome numbers are different between forms of chrysanthemum,the chromosome numbers in the small inflorescences cultivars, cut chrysanthemum ofstandard forms and spray forms, and potted chrysanthemum with large inflorescencesranged from 49 to 57, 49 to 55, 48 to 56, and 49 to 62, respectively. Previous reports andour present study showed that flower diameter was correlate to chromosome number inpotted chrysanthemum, but not in cut cultivars. And the number of 57 was critical point forall the chrysanthemum cultivars, more chromosome numbers were observed solely inlarge-flowered cultivars which mostly consist of potted cultivars with large inflorescences.The present frequency of B chromosomes differed among different chrysanthemumcultivars. The highest frequency of B chromosome as high as 21.88% occurred in pottedcultivars with large inflorescences. Whereas, in cut chrysanthemum and those with small inflorescences cultivars, the frequency of B chromosome were relatively lower, it variedrandomly depending on the individual cells observed. B chromosomes occurred morefrequently in aneuploid cultivars than in euploid one.(3) Chromosome modality was diverse. No significant difference in the chromosomelength among cultivars observed, the longest chromosome ranged from 4.16% to 6.09%,the shortest chromosome ranged from 1.80% to 2.98%. The most chromosomes of allcultivars were reversely symmetrical metacentric (m) and submetacentric (sm)chromosomes. However, the anisomerous acrocentric (st), telocentric (t) and Telocentric (T)chromosomes were fewer. Moreover, the locations of the centromeres were divergent. Theanisomerous chromosomes (st, t, T) were small ones located at the tactic tail of genome.The potted cultivars with large inflorescences were more diversiform than other forms inthe locations of different centromere of chromosome. Secondary constriction presented notonly on the short arm, but also on the long one, and the numbers were more in pottedcultivars with large inflorescences than in the small-flowers forms and cut cultivars.Satelalite was very tiny and mass punctuate, and the frequency of presence was rather low.The karyotype types were characterized as type "2A" or "2B", respectively. Indexs ofkaryotype symmetry were diverse among different cultivar forms, the longest chromosomeversus shortest one (Lt/St) of the potted cultivars with small inflorescences was between1.62 and 2.39, and the asymmetry index (As.K%) ranged from 60.36% to 63.14%; Lt/St ofthe ground cover cultivars all was 2, and As.K% ranged from 59.74% to 63.37%; Lt/St ofcut chrysanthemum with standard forms was between 1.64 and 1.89, and As.K% rangedfrom 63.00% to 67.32%; Lt/St of cut cultivars with spray forms was between 1.83 and 2.42,As.K% ranged from 62.39% to 66.03%; Lt/St of potted cultivars with large inflorescenceswas between 1.52 and 2.83, As.K% ranged from 60.60% to 65.72%.Karyotype analysis further indicated ornamental chrysanthemums were allopolyploid.Diversity of the karyotype among cultivars not only resulted from the configurablevariation of the chromosome, but also likely dues to the recombination of the chromosome.For each cultivar, chromosome modality was overall similar between cells with differentchromosome numbers, except occasionally occurred deletion or duplication in separatechromosome or chromosome pair. It suggested that genome aberrance in the same cultivarwas relatively simple.On the other hand, it is reasonable to classify the chrysanthemum cultivars intodifferent forms in terms of flower diameter and use. The cultivars with small inflorescences was ancient and original correspondingly, while the cut cultivars was relative evolved.However, the genetic background of potted cultivars with large inflorescences was complex,the ancient and evolved cultivars were coexisted, the evolution degree was intermediatebetween the above two forms of chrysanthemum. For cut chrysanthemum, the genome ofspray forms was more active than other forms. Furthermore, karyotype also showed thatanemone type was evolved type in tubuliflorescence.2. Edible chrysanthemumThe three edible cultivars all showed the interphase nuclei was categorized as theintermediatet type between the simple chromocenter type and complex chromocenter type,and the mitotic prophase chromosomes were the interstitial type. The chromosome numberof' Baohuatangyijin' varied from 55 to 62, and Karyotype formula was 2n=54=38m+12sm+4st in 'Zifengrnudan', 2n=55=38m+15sm+2st in 'Jingxingxiying'. Karyotype symmetry ofthree edible cultivars were higher than those in ornamental cultivars. Meiotic process ofpollen mother cell (PMC) was normal and simultaneous cytokinesis. The chromosomepairing at meiotic metaphaseⅠ(MⅠ) were various in different cells. The configuration inMⅠper PMC was 0.94Ⅰ+25.07Ⅱ+0.14Ⅲ+0.63Ⅳin 'Zifengrnudan', and1.32Ⅰ+24.64Ⅱ+0.16Ⅲ+0.85Ⅳ+0.05Ⅴ+0.04Ⅵin 'Jingxingxiying'. However, theseparation was normal during anaphaseⅠand anaphaseⅡ, the abnormality rate was lowerthan 1%. The results indicated that three edible chrysanthemum were all allopolyploid,more ancient and original than ornamental cultivars. But edible cultivars has closer geneticrelationship with ornamental cultivars than medicinal ones do.