| Chromosome pairing in the present F1 hybrids was analyzed based
on this principle of the genome analysis (Ohta and Tanaka 1983; Ohta 1988).
Ae. uniaristata, Ae. caudata and Ae. umbellulata were concluded
to be distantly related to Ae. mutica, because even their 0B hybrids
with Ae. mutica showed a low frequency and a complicated configuration
of A-chromosome pairing and because their 2B hybrids showed a drastically
low frequency of A-chromosome pairing. Ae. bicornis, Ae. longissima,
Ae. sharonensis, Ae. comosa and T. boeoticum showed a good genomic
affinity with Ae. mutica and their 0B hybrids with Ae. mutica
showed a high frequency and an almost regular configuration of chromosome
pairing. However, their genomes were concluded to be only homoeologous with
that of Ae. mutica because their 2B hybrids with Ae. mutica
formed 14 univalents of A-chromosomes. In contrast with those species, both
the 0B and 2B hybrids from the crosses of Ae. speltoides or Ae.
squarrosa x Ae. mutica showed a high frequency of A-chromosome
pairing. In addition, most of the 0B hybrids between Ae. speltoides
and Ae. mutica formed some degree of normal pollen grains and egg
cells with seven chromosomes while those from the crosses of the other species
including Ae. squarrosa x Ae. mutica were almost completely
sterile. These results indicate very close genetic relationship between
Ae. mutica and Ae. speltoides and I propose that the genome
symbol Sm to Ae. mutica as a closely related genome to
the genome S of Ae. speltoides. Sakamoto (1973) classified the genera of the tribe Triticeae into two major groups from their geographical distribution: the Arctic-temperate group and the Mediterranean group. He concluded that the establishment of the former group in the Late-Tertiary is earlier than the establishment in the Quaternary of the latter including the genera Aegilops and Triticum. Ae. mutica is the only species in the genera Aegilops and Triticum that has a lot of morphological characteristics common to the genera of the Arctic-temperate group. Moreover, the karyotype of Ae. mutica consists of only the chromosomes with median and submedian centromeres and Ae. mutica is almost self incompatible while the other species in the genera Aegilops and Triticum are more or less self compatible. These characteristics of Ae. mutica are common to the genera of the Arctictemperate group, and according to Stebbins (1957) self compatible plant species are most probably always derived from self incompatible species. From these evidences Ae. mutica is thought to be the least specialized from the other genera of the tribe Triticeae among the species of the genera Aegilops and Triticum. And from these facts, I conclude that, in the genera Aegilops and Triticum, Ae. mutica is the most similar to the putative common ancestor of this plant group. References Ohta S (1988) Further evidence for the close genetic relationship between Aegilops mutica Boiss, and Ae. speltoides Tausch. Proc. 7th Int Wheat Genet Symp, Cambridge, pp 133-138 Ohta S and Tanaka M (1983) Genome relationships between Ae. mutica and the other diploid Aegilops and Triticum species, based on the chromosome pairing in the hybrids with or without B-chromosomes. Proc. 6th Int Wheat Genet Symp, Kyoto, pp 983-991 Sakamoto S (1973) Patterns of phylogenetic differentiation in the tribe Triticeae. Seiken Siho 24: 11-31 Stebbins GL (1957) Self fertilization and population variability in the higher plants. Amer Nat 91: 337-354 |
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