National Agriculture and Food Research Organization (NARO), in collaboration with Okayama University of Science and Akita Prefectural University has revealed that Japanese chestnuts are genetically divided into four groups such as wild chestnut from Kyushu, western Japan & Tohoku region and cultivated chestnut. The ancestors of wild chestnuts in western Japan and Tohoku region and present cultivated chestnuts were estimated to be diverged around the same time about 20,000 years ago. It has been suggested that Japanese chestnut may have been cultivated and selected artifically since ancient times. This research result is expected to elucidate the domestication process of Japanese chestnut, and contributes to the effective preservation of chestnut genetic resources and the breeding of chestnut varieties using abundant genetic resources.
Overview
Japanese chestnut is a fruit tree native to Japan, and many carbonized nuts and wood have been excavated from ruins from the Jomon period. This fruit is also mentioned in ancient literatures such as the Nihon Shoki, Kojiki, and Honshokukan and has been an important food crop since recorded history. Especially in the Tanba region, which straddles Osaka, Kyoto, and Hyogo prefectures, it is said that varieties and cultivation techniques developed after the Edo period and spread throughout the country. However, until now there has been little scientific evidence to support the history of Japanese chestnut domestication, and many mysteries remain regarding its origins.
NARO used the MIG-seq method (multiplexed ISSR genotyping by sequencing) to analyze the genetic relationship between wild chestnuts distributed throughout Japan and cultivated chestnuts. It was found that Japanese chestnuts can be genetically classified into four groups: wild chestnuts from three regions such as Kyushu, western Japan, and Tohoku, and cultivated chestnuts. It was suggested that these four groups first diverged about 50,000 years ago from the wild chestnut group in Kyushu, followed by three groups such as wild chestnut from western Japan and Tohoku and cultivated chestnut that diverged at the same time about 20,000 years ago. Until now, it was generally believed that cultivated chestnuts were improved from wild chestnuts from the Tanba region in ancient times. However, the estimated time of divergence is earlier than the Jomon period, and it has become clear that it is genetically distant from wild chestnuts in any region, including the Tanba region. This suggests that cultivated chestnuts may have gone through a complex domestication process, such as being brought in from different regions or being artificially selected in multiple regions.
This result is expected to lead to elucidation of the domestication history of Japanese chestnut, and also contributes to the preservation of wild chestnut genetic resources and the breeding of chestnut varieties. The collected wild chestnuts are adapted to the climate of each region from Kyushu to Hokkaido and have a variety of genes that cultivated chestnuts doesn't possess. At NARO, these wild chestnuts are used as materials for cultivar breeding with the aim of increasing regional adaptability and genetic diversity.
Publication
Nishio, S., Takada, N., Terakami, S., Takeuchi, Y., Kimura, M. K., Isoda, K., Saito, T & Iketani, H. (2021). Genetic structure analysis of cultivated and wild chestnut populations reveals gene flow from cultivars to natural stands. Scientific reports, 11(1), 240.
Nishio, S., Takada, N., Takeuchi, Y., Imai, A., Kimura, M. K., & Iketani, H. (2023). The domestication and breeding history of Castanea crenata Siebold et Zucc. estimated by direction of gene flow and approximate Bayesian computation. Tree Genetics & Genomes, 19(5), 44.
