Thai rice archaeobotanical study win Ben Cullen prize

A recent paper from the UCL Early Rice project has received the  BenCullen prize from Antiquity for 2019 (jointly with other excellent papers). The paper, “Social responses to climate change in Iron Age north-east Thailand: new archaeobotanical evidence” publishe last year, by a co-authorship team lead by Cristina Castillo (UCL), together with Katie Miller (MSc Environmental Archaeology, UCL, 2014), as well as colleagues from Oxford, Charles Higham from New Zealand and Nigel Chang (Australia) has shared this prestigious prize.

The study is based on a long a long regional sequence of archaeobotanical data in northeast Thailand between 3100 BP and 1300 BP from archaeobotanical analyses at Ban Non Wot and Non Ban Jak, both near modern Phimai. In this sequence dry rice weeds decline as wet rice weeds appear around 2100 BP, with an increase in the wet rice and disappearance of dry rice weeds by 1500 BP. This indicates that in the face of increasing aridity rice cultivation was bolstered by irrigation, but it also suggests that increasingly hierarchical societies in the region were investing increasing labour in more intensive, wet rice production. This indicates that wet rice cultivation in the Southeast was a secondary development driven by growth of social complexity, and perhaps population growth, rather than driving the demographic underpinnings of the initial Neolithic in the region. It can also be seen that in this region climatic conditions that made it harder to grow rice based on rainfall lead to cultural techniques that altered the environment to make this crop possible. While rainfed rice has persisted in the hills of Southeast Asia into recent times, throughout most of the plains wet rice cultivation has been the predominant cultivation system which has supported historically known states and urban systems in the region (as aptly described for the past millennium in James Scott's Art of Not Being Governed). The beginnings of these dynamic between wet rice states and hill tribes could have only started form the Iron Age onwards. 

Weed evolution by de-domestication: the case of rice

The study of weed origins and evolutionary history is the poor cousin of the archaeobotany of crop domestication. Archaeobotanists can potentially do much more on this, and undoubtedly should. To provide some inspiration it is worth considering some recent insights from genetics, to do with weedy rice. While it is surely the case that rice's wild progenitors may act as weeds in the crop, it now appears that much weedy rice is descended from the crop and not directly from the wild progenitor. A recent paper in Genetic Resources and Crop Evolution by Zhang et al. explores the variation in weedy rices in southern China (Guangdong) and northeast China (Liaoning). In Liaoning there are no wild progenitor populations so it is cultivated fields or their margins which provide the only real habitat for spontaneous rices. In Guangdong by contrast there are populations of wild O. rufipogon. Based on microsatellite markers they show that weedy rice in each region clusters with crops, which represent indica and temperate japonica rices, and the weedy rices are distant from true wild populations. They take this to support the hypothesis that weedy rice is secondarily derived from the crop.

Last year this hypothesis also got support from an anatomical study of weedy rice in the USA, by Thurber, Kepler and Caicedo in BMC Plant Biology which shows that the abscission layer which leads to shattering is clearly distinct from non-shattering domesticated rice but also differs from shattering wild rices in terms of its timing in development: it breaks down sooner leading to earlier shattering than in wild rice. This presumably is an useful adapation for beating the farmer to it and getting into the seedbank before the rice harvest. Thurber et al conclude that this points to unidentified regulatory genes that allowed weedy rice, derived from the crop, to reacquire wild-type shattering. (Whether one might be able to tell weedy from wild rice on the physical remains of spikelet bases is another matter, but surely worthy of investigation by an archaeobotanist!). What is more,  genetic characterization (Thurber et al 2010 Molecular Ecology) found that these weedy rices all possessed the sh4 mutation that characterizes domesticated non-shattering rices! This points unambiguously to the acquisition of a different novel mutation that allows shattering. A few years ago Londo & Schaal (in Molecular Ecology) did some haplotyping of American weedy rices and found mutliple origins, with haplotypes from japonica, indica and aus rices (as well as some hybridization).

So rice has a proclivity to weediness, as with many other crops, and the wild progenitor per se may be less to blame. Contrast this with crops that have been domesticated from weeds (oat, rye, kodo millet) and we can begin to think about alternative pathways to and from being a weed.

Weeds of Australia database

Just found this. Some basic info on a wide range of "weeds," often with seed images. Includes a bunch of things exotic to Australia that most of us would not regard as weeds, like olives and peaches(!), but it may be a useful resource: http://keyserver.lucidcentral.org/weeds/data/03030800-0b07-490a-8d04-0605030c0f01/media/Html/Index.htm

More on rice and millet in South China and Southeast Asia

Some new publications highlight new research and new researchers working on the archaeobotany of parts of China and Southeast Asia. Three recent papers all from among a new generation of archaeobotanists report and review evidence for archaeological rice and foxtail millet (Setaria italica) in the parts of China and in Thailand. Recently published in Archaeological and Anthropological Sciences, is a paper by Nasu et al. on "Land use change for rice and millet at Chengtoushan" a Daxi era (4500-4000 BC) site in Hunan province. This reports in detail the weed flora, mainly indicative of wet rice cultivation (on , as well as discussion of probable rainfed foxtail millet, the earliest South of its probably northern Chinese areas of origin, as well as plausible Perilla and melon (Cucumis melo) cultivation. Two papers have also appeared in the journal Rice from a conference on agriculture and language-spread held at Cornell in September, both by PhD students. One by Jade Guedes, who is carrying out new primary archaeobotanical research in Sichuan province, reviews "Millets, Rice, Social Complexity, and the Spread of Agriculture to the Chengdu Plain and Southwest China." The other, by one my PhD students at UCL, Cristina Castillo, reviews the archaeobotanical record from Thailand: "Rice in Thailand: The Archaeobotanical Contribution". Both also discuss weed flora, including evidence for wet rice cultivation in the case of the Chengdu Bronze Age and dry, rainfed rice in the case of Iron Age southern Thailand.