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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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