Wheat genetics entered a fresh phase with the discovery of the polyploid relationship in this genus. Since then partially sterile hybrids between two parents with different chromosome numbers, such as pentaploid combinations, have been studied extensively by many workers both genetically and cytologically. The present writer has begun in those days his studies on wheat (1919-1924) when he was given the material (seeds of 5x-hybrids and parental species) by Dr. Sakamura, who went abroad shortly after his discovery mentioned above to study plant physiology.

In the course of these investigations, the present writer came to the conclusion that the polyploid series in wheat species might have originated from hybridization followed by doubling of the chromosome numbers of the hybrids. The genome types for the 3 groups were determined to be AA (einkorn), AABB (emmer) and AABBDD (dinkel). As the third genome of 6x-wheats is the specific one to the dinkel group, it was designated by D.

D was soon found by Sax (1928) as a constituent genome of Aegilops cylindrica, a tetraploid species whose another genome was identified with that of Ae. caudata (C). This finding gave a new key to the solution on the origin of common wheat. However, the finding of a diploid species with D genome had to wait until 1944, when T. spelta was synthesized from colchicine treatment of the hybrid, T. dicoccoides x Ae. squarrosa, by 2 American authors, McFadden and Sears. Similar results were obtained by Kihara and Lilienfeld. This time the chromosome doubling was obtained by the union of unreduced gametes in F₁.

We don't need to describe details of the recent advances in wheat genetics. But we can not fail to mention a unique accomplishment, namely the establishment of 21 nullisomics. This work was accomplished by Sears, while Matsumura found 7 nullisomics of the D genome.

There are still many new discoveries which might be compared with that of polyploidy in 1918. However, we might be justified to commemorate the epoch-making discoveries and pay our sincere homage to Dr. Sakamura, Emeritus Professor of Hokkaido University, Japan, and Dr. Sax, Director of Arnold Arboretum, U.S.A., for their pioneering contributions in the field of wheat genetics. Indeed it was the milestone in the first half of this century.

(Received May 20, 1958)