GIFU UNIVERSITY
Faculty of Agriculture, 1-1 Yanagido, Gifu 501-1193 Japan.
Nobuyoshi Watanabe.
Wheat Near-isogenic Lines (156 pp, Sankeiha, Nagoya, Japan;
ISBN 4-88361-131-0) have been the theoretical basis to catalogue
the NILs of the spring wheat Novosibirskaya 67 developed by S.
F. Koval and V. S. Koval and durum wheat LD222 developed by N.
Watanabe. Near-isogenic lines developed by the other research
groups also have been included. The book is available upon request
to the author (E-mail: watnb@cc.gifu-u.ac.jp). See p. 13 for further information.
A NIL for brittle rachis in Ae. tauschii is now available. Aegilops tauschii is diploid species and donor of D genome to hexaploid wheat. The tough-rachis mutant of Ae. tauschii is known as a spontaneous mutant. The tough-rachis mutant was used as a recurrent parent. The isogenic pair can be utilized as material for studying the domestication of wheat.
JAPAN INTERNATIONAL RESEARCH CENTER FOR AGRICULTURAL SCIENCES (JIRCAS)
Tsukuba, Ibaraki 305-8686, Japan.
Hiro Nakamura.
Hexaploid wheat appeared about 7-10 thousand years ago in the Middle and Near East (the west coast of the Caspian Sea) and was then transmitted from its origin to Europe, Africa, southern Asia (Pakistan, India, and Nepal), and China. We know that some hexaploid wheat varieties were transported along the Silk Road through China to the Far East and Japan. Little is known, however, about the actual route of transmission of hexaploid wheat into Japan.
In this study, we analyzed the distribution of the Glu-D1f allele throughout Asia to determine the route by which hexaploid wheat reached Japan, the most geographically remote region of hexaploid wheat production in the world. These studies concentrated predominantly on the variation of the HMW-glutenin Glu-D1f allele and the factors that affected its distribution in different parts of the world. The allelic composition of the HMW-glutenin subunit from 131 improved Japanese cultivars and 174 Japanese, 353 Chinese, 150 Turkish, 3 Syrian, 6 Israeli, 4 Iranian, 1 Iraqi, 23 Indian, 15 Pakistani, 7 Bhutanese, 66 Nepalese, 1 Myanmar, 1 Filipino, 2 Thai, 3 Indonesian, 46 Taiwanese, and 21 Afghani landraces of hexaploid wheat were investigated using SDS-PAGE. The 353 Chinese wheat cultivars were from Heilongjiang, Jilin, Liaoning, Hebei, Beijing, Shandong, Shanxi, Hangzhou, Zhejiang, Henan, Jiangsu, Ningxia, Gansu, Xinjiang, Sichuan, Anhui, and Jiangxi provinces. The Japanese, Chinese, and other Asian hexaploid wheat materials were provided by the National Institute of Agrobiological Resources (NIAR) at Tsukuba in Japan.
The Glu-D1f allele has been reported to be a rare allele when studying the worldwide distribution of Glu-1 alleles. Data also indicate that the products of this allele are more common in Japanese wheat seed-storage proteins than anywhere else bread wheat is grown. We have shown that the Glu-D1f allele is more common in Japan than elsewhere in Asia. The allelic frequency of this subunit is in excess of 35 % among improved Japanese cultivars and 25.3 % among Japanese landraces, whereas it was found in only five cultivar of Chinese (two Xinjiang, one Jiangsu, one Zhejiang, and one Beijing cultivar) and two Afghani wheats.
The carriers of the Glu-D1f allele are distributed across a limited region of Asia, only in southern (Kanto, Tokai, Kinki, Chugoku, Shikoku, and Kyushu areas) and northern (Hokkaido, Tohoku, Hokuriku, and Nagano areas) Japan; in Xinjiang (northwest), Jiangsu and Zhejiang (southeast), and Beijing (northeast) China; and in Afghanistan. However, the allele is rare in wheat varieties from north Japan, China, and Afghanistan. The frequencies of Glu-A1, Glu-B1, and Glu-D1 alleles in hexaploid wheat cultivar from different countries are known to differ. A noticeable geographical cline has been reported in the frequency of the Glu-D1f allele in Japan. To elucidate the factors involved in the establishment of this cline, I investigated the association between the occurrence of the Glu-D1f gene with winter habit and with flour hardness. Because the Japanese islands extend a considerable distance from north to south, they provide a diverse range of environments in which wheat is cultivated. Improved Japanese cultivars and different locally grown landraces are diverse in their type of winter habit. The degree of winter habit in Japanese wheats is the most important factor for hexaploid-wheat production. Generally, the weaker winter-habit wheat cultivars are grown in southern Japan and those with a stronger winter habit are grown in the north. A strong correlation was observed between the intensity of the winter habit and the occurrence of the Glu-D1f allele. Improved cultivars with weaker winter habit tended to have the Glu-D1f allele more frequently than those with strong winter habits, whereas the allele was absent in the cultivars with the strongest winter habit.
The Glu-1 alleles were previously reported not to be associated with ecogeographical parameters in a worldwide context. However, results from our studies suggest that the Glu-D1f allele is associated with ecogeographical parameters within Japan, a finding of great interest to Japanese wheat breeders and cereal chemists. In Afghanistan, Xinjiang in northwest China, Jiangsu and Zhejiang provinces in southeast China, and in southern Japan, spring and facultative types are sown in the autumn or in the spring, respectively. This type of cultivation is specific to these regions. Genotypes that were suitable for this type of hexaploid-wheat cultivation in China may have been selected for during the process of transmission to Japan. All cultivars with the Glu-D1f allele in northern Japan are sown in the autumn, both spring and facultative types. These results suggest that there are no other wheat cultivars in any other region in Asia that possess the Glu-D1f allele.
Until recently, Japanese hexaploid wheat breeders did not manipulate the Glu-1 alleles intentionally. Japanese hexaploid wheat is characterized by the high frequency of alleles such as Glu-D1f. Natural and artificial selection in Japan is thought to have narrowed the genetic base of Japanese hexaploid wheat and this conclusion is supported by the frequent occurrence of the Glu-D1f allele. The unique composition of Glu-1 alleles in Japanese hexaploid wheat will be of considerable interest to both Japanese wheat breeders and cereal chemists. Japanese, hexaploid wheat-breeding objectives mainly determine the requirements for the production of soft white noodles (Udon) in areas where they are eaten frequently. On the other hand, in areas where bread is more commonly consumed, the similarity in Glu-1 allele composition among countries seems to be mainly determined by similar breeding objectives. This study has shown that the Glu-1 allele frequencies differ between noodle-culture zones such as Asia and bread-culture zones such as Europe and the U.S.A. The Glu-1 alleles are reported to directly affect wheat-gluten quality. Therefore, in Japan, Japan-specific differences in Glu-1 patterns are likely to occur because of the intensity of selection pressure towards good, soft noodle-making qualities as compared to selection for good bread-making qualities.
In the course of its long journey and adaptation to diverse local environments, Japanese hexaploid wheat appears to have depleted its genetic diversity. The frequency of the Glu-D1f allele differs between the Japanese and the other Asian, hexaploid-wheat cultivars. Therefore, all Japanese wheat cultivars possibly have a common heritage, which explains the similarities in Glu-1 patterns for all Japanese wheat. There were four routes by which people moved across Asia in ancient times. The first of these routes, the so-called Silk Road, ran through Afghanistan; Xinjiang (northwest), Gansu and Shanxi (northeast), and Jiangsu and Zhejiang (southeast) provinces in China, eventually reaching Japan. The second route ran through Pakistan, India, Myanmar, and then to the Yunnan province in China. A third route ran through Nepal or Pamir, Tibet, and into the Sichuan province in southwest China or the Shanxi province in northeast China. The final route was directly into southern China by boat from India. The distribution of the Glu-D1 alleles is very interesting considering these four routes across Asia. Of all the Glu-D1 alleles, Glu-D1a and Glu-D1f are common in Japanese hexaploid wheat. The Glu-D1a allele was common in wheat cultivars from all over Japan, whereas Glu-D1f is present predominantly in the south. This finding may suggest a transmission pattern for hexaploid wheat in Japan. The first hexaploid wheat (characterized by Glu-D1a or Glu-D1f alleles) arrived in Japan and became distributed across southern Japan. Wheat was then distributed northwards through Japan. As a consequence, northern Japanese hexaploid wheat cultivars predominantly have the Glu-D1a allele. This allele is linked to a gene that makes the wheat suitable for cultivation in the colder winters of northern Japan. The Glu-D1f allele is not linked to this trait. The high frequency of the Glu-D1f allele in southern Japanese wheats may be due to the selective advantage conferred either by Glu-D1f itself or by the action of another linked gene. Whichever gene is responsible, it confers a trait that is suitable for cultivation in southern Japan, such as the intensity of winter habit or be responsible for wheat-flour quality.
The Glu-D1f allele has been regarded as a characteristic glutenin allele for Japanese hexaploid wheat cultivars. In fact, although many hexaploid wheat cultivars in southern Japan possess Glu-D1f, most of the northern Japanese cultivars do not. By comparison, a-amylase isozyme types shows that both types A and J are common in Japan. Type A was found throughout Japan, whereas type J was present predominantly in southern regions. This distribution of a-amylase isozyme types is similar to that of Glu-D1f alleles in Japanese hexaploid wheat. In this study, the specific distribution of an adaptively neutral characteristic (the Glu-D1f allele) suggested a transmission route for hexaploid wheat into eastern China and far-east Japan. Introduced from Afghanistan, Glu-D1f moved through the Xinjiang province in northwest China, into the Jiangsu and Zhejiang provinces in southeast China, and then into southern Japan along the so-called Silk Road. The results presented here indicate that analysis of the Glu-D1f allele is a powerful tool for investigating the real transmission routes of hexaploid wheat across Asia and into far-east Japan.
Acknowledgments. The author thank Drs. T. Hayashi and H. Fujimaki for helpful discussion and comments. Thanks are due to National Institute of Agrobiological Resources (NIAR) at Tsukuba, Japan, for providing hexaploid wheat samples in this study.