東南アジアにおけるサトイモの遺伝的多様性のマッピングによる栽培化モデルの検証（2017-2021）

目的・内容

To test old and new domestication models we will continue to map the distribution of wild populations of C. esculenta, record their morphological diversity, collect leaf tissue samples for DNA analysis, and then compare the wild populations with cultivatedC. esculenta and wild Colocasia species using DNA tests for past hybridization. This year our main target areas are India and Borneo.

活動内容

2020年度活動報告

Surveys and sample collections were carried out in Thailand and Malaysia. In 2020, a new collaboration with the Universiti Malayasia, Sarawak, was started. In addition to samples from wild taro (C. esculenta), samples were obtained from C. fallax, C. lihengiae, C. oresbia, and C.
spongifolia (sp. nova). With these, selected nuclear and chloroplast genome loci were sequenced (2019-2020), revealing: (i) a possible westerneastern Sundaland divide in the genetic diversity of wild taro (C. esculenta), (ii) natural wild taro populations in a vast karstic region
located in northern Vietnam and southern China, and (iii) apparent hybrids between taro and other Colocasia species.
　
In 2020, DNA analysis was extended to include full chloroplast genome sequences from multiple Colocasia species, providing a strong new phylogenetic model for the genus. This shows that taro (C. esculenta) is a polyphyletic taxon in terms of plastid genetic diversity, a finding that has major implications for the evolution and taxonomy of wild and cultivated forms of taro. This and our survey results point to the need for deeper study of the nuclear genome in Colocasia species. In a new collaboration with the Graduate School of Bioagricultural Sciences, Nagoya University (2020), a pilot HPLC experiment was carried out to observe some of the chemical diversity present in wild Colocasia species. This work suggests a possible focus for the study of nuclear genome diversity in taro: relationships between chemical ecology, plant signals, and domestication history.

2019年度活動報告（研究実績の概要）

Fieldwork and research discussions were carried out in three countries: India (15th September to 1st October 2019), Bangladesh (3rd to 8th November, 2019) and Thailand (13th to 24th January, 2020). The visit to India was hosted by Prof. A. Dasgupta (Department of Sociology, Delhi University), and included a visit to the Acharya Jagadish Chandra Bose Indian Botanical Garden. The visit to Bangladesh was hosted by Prof. Md.
A. Hossain (Department of Genetics and Plant Breeding, Bangladesh Agricultural University). The visit to Thailand was hosted by Prof. D.Sookchaloem (Department of Forest Biology, Kasetsart University). Wild taro populations were recorded in India, Bangladesh and Thailand. Work continued on DNA sequencing and analysis, ex situ observation of living plants of wild Colocasia species, and writing.

2019年度活動報告（現在までの進捗状況）

Active (and continuing) research contact was established with researchers in India, Bangladesh and Thailand. Wild taro populations were found to be abundant in West Bengal and Bangladesh (regions within the Gangetic plain and delta), and in the Chao Praya delta of Thailand (vicinity ofBangkok). Valuable samples for future analysis were received from Bangladesh and Thailand.

2018年度活動報告

In FY 2018, fieldwork was carried out in central Vietnam, and pilot studies were made in the delta of the Chao Praya River, near Bangkok, and innortheastern Bangladesh, in and around the Sylhet Basin. Working relationships were established with local researchers, and formal agreements forcooperation are now being prepared for collaboration with Kasetsart University, Bangkok, and Bangladesh Agricultural University, Mymensingh. Aformal affiliation with Dehli University has been established, and I am now attempting to obtain a research visa for visiting India in the nearfuture.In October, 2018, we carried out fieldwork in lowland and mountain areas around Hue city, central Vietnam. We collected samples from 43 sites,and discovered a previously undescribed species of wild taro in mountains near Hue and near the border between Hue and Laos. This appears to bethe same as a wild species seen in 2017 in Yunnan, and is an important discovery for understanding the evolutionary history of Colocasia species.New DNA sequence results were obtained for samples collected in 2017 in southern and northern Vietnam and southern China. The results confirmthat Colocasia sp. nova “spongifolia” (in Yunnan) is a distinct species, and that some lowland populations of wild taro include mixtures of twodifferent evolutionary lineages identified by chloroplast DNA analysis. By comparing chloroplast and nuclear DNA sequences at the same time, wehave found evidence for hybridisation between different evolutionary lineages of C. esculenta, and between different species of Colocasia.

2017年度活動報告

(a)サトイモの自生群におけるDNA配列変異の分析
台湾、フィリピン北部ですでに収集していたColocasia formosanaの標本についてDNAを抽出し葉緑体と核の遺伝子座のプライマーを使い配列を得た。これにより、 C. formosana と他のColocasia 種を識別することが可能になり、また、C. formosana内にかなり多様性があり、フィリピンのものは台湾で広範に見られる変異株と最も類似性があることがわかった。台湾とフィリピンの類似性と地理的隔離はこの共通して見られる変異株が年代的に古いもので長く安定していることを示す。アジア太平洋地域の栽培種についてこれまでに出版したデータと比較すると、栽培種は選択、栽培化、拡散を通じて厳密な遺伝子の隘路を通過したことを示している。

(b)野外調査と標本収集
ベトナムと中国南部のメコン川流域、紅河流域、珠江流域で野外調査を行い標本を収集した。形態学的特徴とColocasia種の同所性から、交雑種とみられる自生群がベトナム北部と中国南部で見つかった。また、自生する野菜として、豚の餌としてコメンサルワイルドなサトイモが利用されていることが確認できた。これらの標本についてはDNAの抽出を開始しており、葉緑体と核の遺伝子座のシーケンシングに取り掛かるところである。