Synthetic Hexaploids Derived from Wild Species Related to Sweet Potato
- Publisher: 日本育種学会
sweet potato | genome analysis | synthetic hexaploid | Ipomoea batatas | interspecific hybrid
mesheuropmc: food and beverages | fungi
The utilization of germplasm of the wild species in sweet-potato breeding has been conducted for the last three decades. Such attempts brought some remarkable achievments in improving root yield, starch content and resistance to the nematodes of sweet potato. Some wild plants in polyploid series may have many genes potentially important for further improvement of the agronomic traits. However, the genomic relationship between the wild relatives and hexaploid sweet potato (2n=6x=90) has been unrevealed. Meiotic studies were carried out on the hexaploids synthesized with diploids and tetraploids and on the F_1 hybrids, when possible, with sweet potato. Chromosomes in pollen mother cells (PMC's) and root tip cells were fixed in New-comer's solution and stained according to Feulgen reaction with Schiff's reagent. The present report was concerned wlth two kinds of the synthetic hexaploids. The first was the hexaploids derived from chromosome doubling of triploid hybrids between Ipomoea lacunosa (K61, 2n=30) and I.tiliacea (K134, 2n=60). the synthetic hexaploid exhibited mostly regular meiosis with bivalents at the metaphase I stage (MI), and it was considered an allo- or segmental allo-hexaploid. The synthetic hexaploids were fertile, but failure in obtaining hybrids by crosses with sweet potato suggested a critical reproductive barrier between them. The second synthetic hexaploids with 2x I, trifida (K221, 2n=30) and 4x I,trifida (K233, 2n=60) showed the chromosome configurations characterized by the occurrence of tetravalents and hexavalents. Such multivalent associations, high in frequency and number per cell, suggested the presence of the genomes at least in quadruplicate. Similar pattern of the chromosome configura-tions was observed in a cultivar of sweet potato and the F_1 hybrid between the synthetic hexaploid and sweet potato. Consequently, the genomic formula for sweet potato was proposed as B1B1B2B2B2B2, in which B1B1 was given to 2x I.trifida and B2B2B2B2 to 4x I. trifida. However, it is necessary to clarify the degree of homology between B1 and B2 genomes for more conclusive genomic constitution of sweet potato. A brief account was given for the taxonomic identification of the wild Ipomoea strains used in the present study.