Phytolith analysis for differentiating between broomcorn millet (Panicum miliaceum) and its weed/feral type (Panicum ruderale)

Jianping Zhang,Minxuan Liu,Xianmin Diao,Naiqin Wu,Konglan Shao,Houyuan Lu

doi:10.1038/s41598-018-31467-6

Abstract

Domestication of broomcorn millet (Panicum miliaceum) is one of the most significant events in prehistoric East Asia, providing sufficient food supply for the explosive growth of Neolithic populations and the transition into complex societies. However, to date, the process of broomcorn millet domestication is still largely unknown, partly due to the lack of clear diagnostic tools for distinguishing between millet and its related wild grasses in archaeological samples. Here, we examined the percentage of silicified epidermal long-cell undulated patterns in the glume and palea from inflorescence bracts in 21 modern varieties of broomcorn millet and 12 weed/feral-type Panicum ruderale collected across northern China. Our results show that the percentage of ηIII patterns in domesticated broomcorn millet (23.0% ± 5.9%; n = 63) is about 10% higher than in P. ruderale (10.8% ± 5.8%; n = 36), with quartiles of 17.2–28.3% and 5.1–15.5%, respectively. Owing to the increase in ηIII pattern percentage correlates significantly with a decrease in the grain length/width ratio, in the absence of exact wild ancestors of broomcorn millet, the characterization of phytolith differences between P. ruderale and P. miliaceum thus becomes an alternative approach to provide insight into origin of broomcorn millet.

Highlights

Broomcorn millet (Panicum miliaceum; a tetraploid cereal, 2n = 4x = 36) is one of the oldest staple cereals in East Asia, dating back to the beginning of the Holocene and used across the entire Eurasian continent prior to the popularity of rice and wheat; it has emerged as one of the most aggressive grass weeds in North America and Canada[1,2,3]
Since phytoliths are silica casts of plant cells created within and between cells of living plants tissues that can remain in sediments long after the living tissue has decayed, phytolith analysis makes the identification of decayed plant remains from archaeological samples possible and exact, i.e., rice, maize, foxtail millet and broomcorn millet can be identified according to shape, size, and other anatomical features[10,11,12,13]
We investigated 21 landraces of modern broomcorn millet and 12 specimens of P. ruderale from eight provinces cross north China in order to determine whether analyzing the phytoliths of inflorescence bracts can be used as an effective tool for discriminating broomcorn millet from its possible wild ancestor or weed/feral type, P. ruderale

Summary

Introduction

To date, the questions of where, when and how the cereal transitioned from simple gathering to domestication remain largely unanswered due to the lack of definite identifiable features distinguishing domesticated broomcorn millet and its wild ancestor. Owing to the highly similar phytolith shape within a given genus, it is not adequate to use morphological features alone to distinguish crop plants from their wild ancestors. The development of phytolith morphometry has enabled such distinctions to be made, and morphometry-based approaches are increasingly used to reveal crop domestication processes These approaches include characterizing the fish-like scales of bulliform phytoliths of rice and the inflorescence phytoliths of millet and wheat[14,15,16,17,18,19,20]

Methods

Results

Conclusion