4. Relationships of Japanese species with Nepalese and American species
After the introduction of materials from South-West Asia search of the genome homology by means of cytological studies, extended into the rest of the Triticeae genera (Matsumura S and Sakamoto 1955; Matsumura S et al. 1956; Sakamoto and Muramatsu 1962, 1963, 1965). Table 2 is a list of wild Triticeae species, which were used for the incipient investigations. However, the investigation was confronted with the barriers in hybridization work. One of the main reasons was the necessity of regulating flowering time to escape the Baiu season, and the second, the inability of endosperm to form mature normal seed. Before overcoming the barrier by embryo rescue, the studies on the cross-compatibility, chromosome pairing and genome analysis became the main subjects followed for decades to the 1980's. To starting with, cross combinations among the same ploidy levels are shown below:
(1) Japanese 4x x Japanese 4x including A. yezoense, A.ciliare and A. gmelinii (Japan),
(2) Japanese 4x x Nepalese 4x including A. ciliare, A.semicostatum, A. yezoense and A. gmelinii (Nepal),
(3) Nepalese tetrap A. gmelinii x A. semicostatum,
(4) Japanese 4x x American 4x: A. ciliare x A. trachycaulum, and
(5) Japanese 6x x Japanese 6x: A. humidum x A.tsukushiense.*

In the combinations involving A. gmelinii, there were problems; pollination was difficult because of Baiu, or a hybrid weakness. However, in the rest of combinations hybrid plant grew vigorous, and the cytological observations are summarized as follows (Table 3) (Sakamoto and Muramatsu 1966a).
(1) Genomes of two Japanese tetraploid species A. ciliare and A. yezoense, are identical with a mode of 7 bivalents, (2) two hexaploid species, A. humidum (A. humidorum) and A. tsukushiense, have identical genomes, (3) genomes of a Nepalese tetraploid, A. semicostatum are closely related to those in Japanese tetraploids, and(4) an American tetraploid species, A. trachycaulum, is distantly related to the Japanese tetraploid, showing low bivalent formations ranging from 2 to 9 (with a mode of 5) bivalents. (5) Complete pollen sterility and high seed sterility were the rule in the interspecific hybrids, despite good chromosome pairing at MI.

Investigation between different ploidy interspecific pentaploid hybrids, are shown in Table 4 (Sakamoto and Muramatsu 1966b). A mode of bivalents numbers 14 in the F₁, A. tsukushiense x A. ciliare supported the result by Matsumura S (1941, 1948). The combinations using A. yezoense and A. gmelinii (Japan) to A. tsukushiense showed essentially similar results. The lower number of bivalents in the tetraploid hybrids between Japanese and Nepalese strains is similarly found in the pentaploid cross combination.

Based on chromosome homology, the genome formulae given at the time were:

Genomic affinity of the Japanese A. gmelinii was deduced indirectly from the results, A. gmelinii (Japan) x A. tsukushiense, A. tsukushiense x A. ciliare and A. tsukushiense x A. yezoense.
5. Further study on hybrid and cytogenetic investigations
Evidently the three genomes of A. tsukushiense are equally differentiated, because a polyhaploid plant showed low chromosome pairing: the highest number of bivalents per cell was 3''+ 5', in only 0.2% of MI cells, and in 84% bivalent was not observed (Sakamoto 1964a). The amount of bivalent formation at MI is equivalent to a polyhaploid in hexaploid wheat. Backcross experiments yielded, however, 27 plants out of 4,018 flowers pollinated, and then only two were monosomic lower than that expected in wheat. Further cross experiment to explore for the cytological relationships was made with other Triticeae genera, Elymus, Heteranthelium , Henrardia, Eremopyrum and Hordeum(Sakamoto and Muramatsu 1963; Sakamoto1967a, 1967b, 1968, 1969, 1971, 1972, 1974). Among them genomes of Heteranthelium (genome designation at present: Q), Henrardia (genome designation: O)and Eremopyrum (genome designation: FXe) are highly differentiated showing little homology to the chromosome of the other genera. On the other hand,the relationships of indigenous Agropyron to Elymus species were important, for they contain common genomes (Sakamoto 1965,1982). Between two Elymus species, E. sibiricus (2n=4x=28) and E. dahuricus(2n=6x=42), there is only one genome in common regardless of the morphological similarities. By contrast,E. dahuricus and A. tsukushiense are cytologically very closely related irrespective of their morphological classification into the different genera. The two species share at least two homologous genomes showing 17.67 bivalents per cell. Sakamoto (1982) concluded that these three species E. sibiricus, E. dahuricus and A.tsukushiense contain one homologous genome in common, and that this genome will be Dewey's S genome (Dewey 1974), which is either I, K or L genome designated for A. tsukushiense by Matsumura S (1941, 1948).

Since Dewey (1974) had reported E. sibiricus is genomically similar to A. caninum and E. canadensis, which contained the H genome from Hordeum besides the S genome. Thus the genome relationship of the Japanese species to other Asiatic and North-American species became clear, and this was a basis for grouping the Japanese indigenous Triticeae species (except E. mollis) into the same genetic group II in Agropymn-Elymus- Sitanion Complex (Sakamoto 1973).