| Reconsideration of the genome of Aegilops mutica
Boiss. based on the chromosome pairing in interspecific and intergeneric
hybrids Shoji OHTA and Masatake TANAKA Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Muko, Kyoto The purpose of the present work is to estimate chromosome homology between the genome of Ae. mutica and those of other diploid Aegilops species and a diploid Triticum species. Eight diploid species, Ae, longissima (SlSl), Ae. bicornis (SbSb), Ae. speltoides (SS). Ae. comosa (MM), Ae. uniaristata (MuMu), Ae. caudata (CC), Ae. umbellulata (CuCu) and T. boeoticum (AA) were crossed by Ae. mutica (MtMt) with or without B-chromosomes, and the pairing of A-chromosomes at MI of PMCs in these F1 hybrids was observed. A very high chromosome pairing with a quadrivalent or a trivalent, many bivalents and a few univalents was observed in hybrids without B-chromosomes (OB hybrids) of Ae. longissima x Ae. mutica and Ae. comosa x Ae. mutica. On the contrary, in almost all cells of hybrids with two B-chromosomes (2B hybrids) of these two cross combinations, only 14 univalents were characteristically observed. And the amount of chromosome pairing in hybrids with one B-chromosomes (1B hybrids) was intermediate between those of OB and 2B hybrids mentioned above. In Ae. bicornis x Ae. mutica, only OB hybrids were obtained. These hybrids formed almost 7 bivalents. Only OB hybrids were obtained from T. boeoticum x Ae. mutica. They showed a very high chromosome pairing and the formation of a ring-shaped quadrivalent was observed only in this cross combination. Hybrids without B-chromosomes of Ae. uniaristata x Ae. mutica, Ae. caudata x Ae. mutica and Ae. umbellulata x Ae. mutica formed much more univalents than OB hybrids of other cross combinations. Moreover, many multivalents were observed in the latter two combinations. And 2B hybrids of Ae. caudata x Ae. mutica formed 14 univalents in most of cells observed. In contrast with the above-mentioned hybrid combinations, a very high chromosome pairing with 10.91 chiasmata per cell was observed in the 1B hybrid of Ae. speltoides x Ae. mutica. This mean chiasma frequency was the highest among all the 1B hybrids obtained in the present work. Moreover, the 2B hybrid of this cross combination showed an evidently high chromosome pairing with 5.14 chiasmata per cell, though some reduction of chromosome pairing compared with the 1B hybrid was observed. Not a few ring-shaped bivalents were observed but no PMCs with 14 univalents were found in this 2B hybrid. It is well-known that the B-chromosomes of Ae. mutica suppress homoeologous chromosome pairing but not homologous one. Considering this fact and the present data, it is clear that the genome Mt is very closely related to S. Mt is also closely related to Sl, Sb, M and A, but not so closely related to Mu. C and Cu. At present, no data are available with the 2B hybrids in Ae. bicornis x Ae. mutica and T. boeoticum x Ae. mutica. |