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5. Study on nucleus-cytoplasm
interactions
By successive backcrosses, nucleus and cytoplasm could be
substituted between two species. This method was first applied for
wheat and Aegilops species by Kihara in 1951, where Ae.
caudata was successively backcrossed with T. vulgare
erythrospermum as the recurrent male parent. This line showed
male sterile with normal growth, that is the firstly developed strain
of cytoplasmic male sterility in cultivated plants. This method has
been widely applied for agronomic hybrid seed production in other
crops and vegetables.
Kihara developed a series of cytoplasmic substitution lines of wheat,
that is, alloplasmic lines of several 6x wheat nucleus having
cytoplasm of various Triticum and Aegilops. Analyses of
phenotipic traits including male fertility/sterility in these lines
indicated that many plant characters were determined by interactions
of nucleus and cytoplasmic genes. Furthermore, utilizing these lines,
his colleagues compared overall characteristics of cytoplasmic
genotypes of Triticum-Aegilops complex, and concluded possible
cytoplasmic (maternal) progenitors of diploid species to polyploid
ones (reviewed by Tsunewaki 1986).
Wheat is the only species in which comprehensive cytoplasmic
substitution lines are available. This is due to another pioneering
contribution by Kihara.
6. Other contribution to wheat research
Other contribution of Kihara to wheat research are listed as
follows:
(1) Right- and left-handedness of wheat seedlings.
(2) Induction of haploid plant by delayed pollination in Einkorn.
(3) Cytological observation of haploid plants.
(4) Collection and conservation of wild species as genetic resources
for wheat breeding.
(5) Stability of growth habitat in wheat species.
(6) Utilization of alloplasmic lines for plant breeding (NC-hybrid
and NC-hetrosis).
(7) Origin of DARUMA: the parental variety of Norin 10.
As described above, Kihara made a great foundation of wheat genetics,
on which modern wheat genetics and breeding base on. Before the
development of molecular biology, this great scientist showed
important evidences which are now alive in modern plant science from
corss-hybridization experiment and cytological observation in wheat
species. It is very important that he was a scientist who found not
only experimental discoveries, but scientific concepts he
established. Also, he was a pioneer who emphasized importance of
conserving genetic strains as keys for biological research, and wild
species as genetic resources for plant breeding. This is another
coincidence to the case of Dr. E. R. Sears who recognized the
importance of establishing genetic strains to develop a series of
aneuploid lines, which were provided to world-wide wheat researchers
for great deal of advancement of genetic reserach.
The concepts Kihara founded, and genetic strains he established, both
would guarantee the further development of wheat researches. In these
senses, it is worthwhile to quote a motto Kihara described in an
article in 1954:
The history of the
earth
is recorded in the layers of its crust:
The history of all organisms
is inscribed in the
chromosomes.
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