The First Domesticated 'Cheongju Sorori Rice' Excavated in Korea

Abstract

Archaeological excavations led by Yung-jo Lee and Jong-yoon Woo were carried out twice at the Sorori paleolithic site, Cheongju, in the Republic of Korea, at the upper stream of the Geumgang river, the Miho riverside. A total of 127 rice seeds were excavated, including 18 ancient rice and 109 Quasi-rice, in 1998 and 2001. At the first excavation, eleven short japonica-type ancient rice and one slender smooth ancient rice with two kinds of Quasi-rice were excavated. The average length of the 11 short rice grains obtained from the first and second excavation was 7.19 mm and the average width was 3.08 mm, respectively. The Quasi-rice are apparently different from the rice and do not have bi-peak protuberances on their glume surface. At the second excavation, six short ancient rice chaffs and some Quasi-rice 2 were found. These short-grained ancient rice were comparable to the ancient rice that were excavated at the Illsan Neolithic site. Geologists and radiologists confirmed that the peat layer in which the rice found was older than 15,000 years. In this study, the morphological characteristics, crushing, and DNA band patterns related to the genetic polymorphism of rice grains in Cheongju Sorori were compared and analyzed for genetic similarities and differences with wild rice, weed rice, and modern rice. The morphological, ecological, and physiological variations in rice grains excavated from the Sorori site were presumed to denote the origin of rice domestication in Korea. It is also suggested that the results of the DNA sequencing of excavated rice are very important clues in estimating the origin of the early domestication of rice.

Keywords: Sorori rice; early domesticated rice; origin of rice; paleolithic; peat layer; quaternary geological layer.

Figure 1

Schematic diagram of the evolutionary pathways of rice grown in Asia and Africa [21].

Figure 2

Location of Sorori site (▼) in Cheongju where the ancient rice was excavated.

Figure 3

Cross-section of the excavated site at Sorori, Cheongju, in Korea. The ancient rice that was excavated was located at the following heights above sea level: Quasi-rice 3 (12,780 bp) about 32.0 m, ancient short rice seed 2 (13,490 bp) about 31.9 m, Quasi-rice seed 2 (14,820 bp) about 31.8 m, ancient short rice seed 1 (13,920 bp) about 31.1 m, and Quasi-rice seed 1 (17,310 bp) about 29.2 m [21].

Figure 4

Carbonized rice and insect fossils excavated from Sorori, Cheongju. (A) Sorori ancient rice in situ; (B) Quasi-rice, in situ; (C) an example of the insect fossils found in the Sorori peat layer; (D) a present specimen of Plateumaris sericea (dark blue variation with violet reflection on wings and green reflection on legs).

Figure 5

Sampling location in Sorori, rice sample, and a stone artifact that could have been used for cutting rice grains from rice plants in the rice field. The white circle means the cutting edge of notched tools.

Figure 6

Comparison and analysis of the morphology of rice seeds excavated in Sorori. (A) Chaff of ancient short-grain rice (japonica type); (B) chaff of ancient long smooth-grain rice (indica type); (C) chaff of Quasi-rice I grain, half only; (D) chaff of complete Quasi-rice II grain; (E,F) chaff of Quasi-rice II grain, half only; (G) Quasi-rice II, complete at the time of excavation; (H) Quasi-rice II, incomplete at the time of excavation.

Figure 7

Analysis of the morphological characteristics of rice seeds excavated from Sorori using SEM. (A) Protuberance of ancient short rice grains (japonica type); (B) protuberance of ancient long smooth rice grains (indica type); (C) protuberance of Quasi-rice grains.

Figure 8

Rice grain distribution in association with grain size and length/width ratio from 200 grains collected Koyang city, and 13 ancient grains excavated at Sorori, Cheongju in Korea. ▲: Gawaji I (n = 10 about BP); □: Gawaji Π (n = 287 about BP); ●: Sorori (n = 13, 15,000 BP). The semi-circule represents a general grain size ratio range that includes seed length/width belonging to existing ecotypes, indica (ID), japonica (JP), and javanica (JV) [24].

Figure 9

Bi-peak protuberances on the surface of glume obtained via SEM [9]. (a) Ancient rice: Short grain (b) Ancient rice: Long grain (c) Quasirice-1: No protuberance (d) Quasirice-2: No protuberance (e) Current cultivar: Hwasung-byo (f) Current cultivar: IR 36 (g) O. glabrmima: African rice (h) O. rulfipogon: Wild rice.

Figure 10

Appearance before the DNA extraction of cultivated rice, weedy rice, wild relatives of rice, carbonized rice excavated from Gawaji, Ilsan, and six types of ancient carbonized rice excavated from Sorori, Cheongju, Korea. 1: IR 36; 2: Pehku; 3: Nagdong; 4: Taichung 65; 5: Gyeongsan Aengmi 2; 6: Suncheon Aengmi 1; 7: Hapcheon Aengmi 3; 8: Seongju Aengmi 8; 9: W1944; 10: W130; 11: Gawaji excavated rice; 12: ancient short-grain; 13: Quasi-rice 1; 14: Quasi-rice 2; 15: ancient short-grain; 16: Quasi-rice 3; 17: Quasi-rice 4.

Figure 11

PCR band patterns of DNA extracted from rice husk using seven multi-range universal primers, URP1, URP12, and URP13.

Figure 12

Phylogenetic analysis of ancient and current rice DNAs extracted from a single hull and amplified by universal rice primers, URP1, URP12, and URP13. The phylogenetic tree was constructed using the UPGMA method by POPTREE2 software with the UPGMA tree displayed using Nei’s standard genetic distance method.

Figure 13

(A) Insect Fossil 1 excavated at Sorori (collection container number: 70); (B) example of extant species specimen—Plateumaris sericea, bronze color variant.

Figure 14

Examples of color variation in modern species of Plateumaris sericea.

Figure 15

Color variation in the excavated fossil species Plateumaris sericea.

Figure 16

Sorori ancient rice grains found at second excavation in 2001.

Figure 17

Ancient rice grains found at Ilsan excavation in 1991.

Figure 18

Scenes of excavation at Sorori site (A-II) in September 2001.

Figure 19

The excavated rice grains and stone artifacts that could have been used for cutting rice grains from rice plants in the rice field at Cheongju Sorori site. The white (B) and red (C) circles mean the cut part of stones and rice grains, respectively.