Intergeneric Hybridization Between Dendranthema And Four Allied Genera

Chrysanthemum(Dendranthema morifolium), is one of the most important floricultural crops in cut flower, potted plant and garden plant. Many chrysanthemum cultivars are weak resistant to disease, insect, virus and environment. But in allied genera, many wild species possess elite attributes such as resistance to biotic or abiotic stresses. In this paper, intergeneric cross has been made to assess the relationships between Dendranthema wild species (♀) and C. chinense (2n=18;(?)), A. myriantha (2n=18;(?)), T. vulgare (2n=18;(?)), O. taihangensis (2n=18;(?)) respectively. Then, as bridge parent, the intergeneric hybrids were hybrided with chrysanthemum to innovate chrysanthemum germ plasm. It made a base for new resistance varieties breeding of chrysanthemum and the results showed as below:(1) No seed was obtained in the combination between C. chinense((?)) and D. indicum (♀), D. crassum (♀).57% and 46% megaspores of D. indicum and D. crassum can develop into a mature embryo sac. In vitro,51% C. chinense pollens germinate, and in planta, germination is observed from 2h to 2d after pollination. And, the development of the hybrid embryo was only arrested at the globular stage. It seems that hybrid embryo abortion is the major means of preventing the formation of intergeneric hybrid combination.(2) Aapplying of ovule rescue with 12 combinations after pollination for 15d, the combination of D. crassum and C. chinense, D. indicum and C. chinense, D. crassum and A myriantha, D. indicum and O. taihangensis and D. nankingense and T. vulgare were obtained hybrid plants. Under natural conditions, no seed was obtained in these combinations. Results showed that ovule culture is a valid method for carrying out and overcoming distant hybridization between Dendranthema and the allied genera.(3) Genomic in situ hybridization experiments were able to successfully distinguish the genomic origin of both mitotic and meiotic metaphase chromosomes in the hybrid. In D. crassum×A. myriantha, a large excess of blocking DNA is necessary to achieve genome discrimination in the hybrid. In contrast, in D. crassum×C. chinense, D. indicum×C. chinense, D. indicum×O. taihangensis, and D. nankingense×T. vulgare hybrids, no blocking DNA is needed to fully discriminate between the parental genomes. GISH analysis suggested distant phylogenetic relationship between Dendranthema and Crossostephium, Tanacetum, Opisthopappus, while Dendranthema is more close to Ajania than the others.The D. indicum×C. chinense hybrid grew and abloomed vigorously in the field, while the D. indicum×O. taihangensis hybrid could not carried out genital growth and D. indicum×T. vulgare hybrid could not grow normally. It showed that the phylogenetic relationship between Dendranthema and the allied genera from close to distant in turn is Ajania, Crossostephium, Opisthopappus, Tanacetum.(4) Artificial hybridizations have been made between the Chrysanthemum cultivar ’tianzhuiyulu’(2n=54;♀) and the intergeneric hybrids ((?)). The seed set of ’tianzhuiyulu’×(D. Crassum×C. chinense),’tianzhuiyulu’×(D. indicum x C. chinense) and ’tianzhuiyulu’×(D. nankingense×T. vulgare) was 22.5%,12.5% and 0.25% respectively. Dual-color genomic in situ hybridization was applied for these hybrids. In ’tianzhuiyulu’×(D. indicum×C. chinense) hybrid, it contained two genomes of ’tianzhuiyulu’ and D. indicum. In ’tianzhuiyulu’×(D. nankingense×T. vulgare) hybrid, it contained two genomes of ’tianzhuiyulu’ and D. nankingense. While in ’tianzhuiyulu’×(D. crassum×C. chinense) hybrids, they contained three genomes of ’tianzhuiyulu’, D. crassum and C. chinense, the artificial hybridizations was an effective way to innovate chrysanthemum germplasm and made it possible for improving chrysanthemum varieties by introducing elite attributes of its allied genera.