Diversity and domestication in the genus Panicum (Poaceae)Harriet V. Hunt1, Mim A. Bower1, Christopher J. Howe2 and Martin K. Jones3

1McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, CAMBRIDGE CB2 3ER 2Department of Biochemistry, University of Cambridge, Downing Site, Tennis Court Road, CAMBRIDGE CB2 1QW3Department of Archaeology, University of Cambridge, Downing Street, CAMBRIDGE CB2 3DZ

Introduction

Panicum is one of the largest grass genera, with over 100 species distributed throughout the tropical and temperate regions of the Old and New Worlds. A number of these are cultivated for their grain, or harvested from the wild: P. miliaceum (broomcorn or proso millet), P. sumatrense (little millet or samai), P. sonorum (sauwi millet), P. atrosanguineum, P. hippothrix, P. trypheron, P. turgidum and others. Broomcorn millet, Panicum miliaceum, appears early in the archaeobotanical record and was an important cereal in prehistory, but its evolutionary and geographical origins remain uncertain. This project is analysing patterns of genus- and species-level genetic diversity to illuminate the domestication history of P. miliaceum.

AcknowledgementsFunding: The Leverhulme Trust, The Wellcome TrustPlant material: Vavilov Institute, St Petersburg, Russia; Millennium Seed Bank Project, RBG Kew; Dorian Fuller, Institute of Archaeology, University College London; David Brenner, Iowa State UniversityPlant cultivation: Alexander Goodall, Cambridge Botanic GardenAFLP analysis: Susan Freeman, NIAB

ReferencesaMK Jones (2004) Ch. 10 in Traces of Ancestry: studies in honour of Colin Renfrew (ed. MK Jones). McDonald Institute MonographsbSS Aliscioni et al. (2003) American Journal of Botany 90: 796-821

Panicum miliaceum L. – an ancient grain cropBroomcorn millet (Panicum miliaceum) shows an unusual geographical pattern in the archaeobotanical record (Fig. 1). It appears in the 7th millennium BC in northern China, and by the 6th millennium BC in Eastern Europe and the Caucasus. In later prehistory, broomcorn millet agriculture spread to Central and Western Europe, to South Asia and to Japan, although it did not reach the Near Eastern Fertile Crescent until the 1st millennium BC, and is absent from the archaeobotanical record of Central Asia.

Today, Panicum miliaceum cultivation for human consumption is still significant in Russia, India and China. It is a short-lived crop with low water and nutrient requirements, making it suitable for cultivation on land that is otherwise marginal for agriculture.

7th – 6th mill. BC 6th – 5th mill. BC1st mill. BC5th – 4th mill. BC

3rd mill. BC 2nd mill. BC

Fig. 1.

Panicum miliaceum in the archaeobotanical reords

Tracking the geography of domestication with genetic markersThree possible hypotheses can account for the distribution of early Panicum findsa:•A single domestication in northern China, followed by extremely rapid westward spread•A single domestication in northern China some millennia earlier than current dates suggest, followed by a westward spread at rates comparable to those of other crops•Two or more domestications, spread across the Eurasian steppe

This project is developing genetic markers to map diversity in broomcorn millet landraces and test these hypotheses. Early results indicate P. miliaceum harbours low genetic diversity in both nuclear and chloroplast genomes. Current work is focusing on AFLPs (Fig. 2) and SNPs in introns of single-copy nuclear genes, specifically FLO/LFY orthologs and the waxy locus.

Fig. 2. AFLP gel: 3 accessions of P. miliaceum analysed using 16 selective primer combinations. Diversity generally low, but some polymorphic loci are present.

Towards a Eurasian Panicum phylogeny

The phylogenetic relationships of Eurasian Panicum species are currently unknown, and the wild ancestor of P. milaceum, if it still exists, has not been conclusively identified. We are sequencing the chloroplast ndhF gene in Old World species (Fig. 3), to complement existing phylogenetic studies of New World Panicumb.

Fig. 3. (L-R) P. capillare, P. dichotomiflorum and P. bisulcatum – widespread wild species in Asia

Chromosome numbers in Panicum indicate that polyploidy is common. Future work should extend the phylogenetic study to nuclear genes, to assess evidence for reticulate evolution through congruence of tree topologies.