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Wheat Information Service
Number 77: 1- 6 (1993)
I. Review
Article
Scientific
contributions of Dr. Hitoshi Kihara to wheat studies
- On the occasion of his centennial -
Tetsuo Sasakuma
Kihara Institute for Biological Research
Yokohama City University, Mutsukawa 3-122, Minami-ku, Yokohama,
Japan
The year 1993 is the centennial of Dr. Hitoshi Kihara, who was a
founder of Wheat Information Service. He was born on October 21, 1893
in Tokyo, and died on July 27, 1987 in Yokohama. Since this 100 years
coincide to the era of development of modern biological science, and
since Dr. H. Kihara had established important concept and methodology
in plant genetics and evolution during this era, it would be useful
to review his scientific contributions for prospecting scientific
development for the next century.
This article aims to introduce his contributions to wheat researches
of genetics and breeding on the occasion of his centennial
anniversary.
1. Study on chromosome of wheat and its relatives
The chromosome numbers of many cultivated plants including wheat
were not identified until Sakamura revealed three kinds of chromosome
number among wheat species in 1918. Kihara followed him by intensive
studies on chromosome karyotypes of Triticum, Aegilops, Secale,
Avena, and Hordeum species showing, three levels of
ploidy, that is, 2x, 4x and 6x in nature with their basic chromosome
number of seven in 1924. Furthermore, from cytological observation of
meiotic chromosome behaviours in these species and their hybrids, he
developed the theory of polyploidy: Among polyploid species there are
two types; one includes identical duplicated genomes, autopolyploidy,
and the other consists of different sets of genome,
allo-polyploidy.
2. Study on interspecific hybrid
Soon after the discovery of three levels of chromosome number of
Triticum, Kihara made a interspecific hybrid between a bread
wheat (6x) and an emmer wheat (4x), called as pentaploid hybrid (2n =
5x = 35), on which progenies chromosome behaviors, were traced. He
found two categories among the progenies concerning their chromosome
constitution; fertile combination and sterile combination. The latter
is the group which showed low fertility and produced few progenies in
the next generation. On the other hand, the former group was
relatively fertile to produce next generation. The fertile group
included plants having chromosome numbers of 28 or 42, which are
stable for fertility and chromosome number in their progenies.
The other plants in this group also tended to converge to 28- or
42-chromosome individuals in their further generations. From these
observations, he drew the conclusion that there must be an unit of
inheritance, named as a genome, which assure a basic constitution of
organism's lives, corresponding to seven chromosomes in the wheat
species.
The concept of the genome was so established as a set of chromosomes
containing all genes necessary to ensure a life (Kihara 1931). This
concept was conflict either with Winkler's one (1920) which
corresponded a haploid set of chromosomes, or with recent utilization
for the term in molecular biology like 'genomic DNA' indicating
nuclear DNA.
Recent advancement of molecular biology indicates that most of coding
genes exist commonly in plant kingdom with the common fashion of
their array along chromosomes. These facts suggest the importance of
reviewing the concept of genome for understanding species
differentiation and evolution.
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