In Rice, More Comprehensive DNA Re-analysis

choi

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supports archaeology, that a single-origin domestication 8 to 9,000 years years ago at Yangtze Valley (of China) and spread to India, rather than the competing proposition that Ganges in India independently accomplished the feat.

研究显示:中国是驯化水稻的原产地. VOA Chinese, May 3, 2011.
http://www.voanews.com/chinese/news/international/20110503-RICE-ORIGIN-121155584.html

, which cites
Molina J et al, .  Proceeding of National Academy Science (PNAS), published online before print May 2, 2011, doi: 10.1073/pnas.1104686108
http://www.pnas.org/content/early/2011/04/27/1104686108.full.pdf+html?sid=fe692533-da9d-4b0d-ba80-41da5d3a5c20

The thesis of the PNAS is in Discussion:

"If we use an estimate for nucleotide substitution rates in the grasses (40), we find a divergence time between O. rufipogon and O. sativa at ∼8,200 y ago and between tropical japonica and indica at ∼3,900 y ago. If we apply the molecular clock rate estimated from the chromosome scan data (SI Text), we obtain an earlier mean date of domestication for rice (13,500 y B.P.). The former molecular estimates are in remarkable agreement with archaeological estimates for the onset of rice domestication in the Yangtze Valley (∼8,000–9,000 y ago) and the expansion of indica rice in South Asia (∼4,000 y ago) (3, 28), and even the latter date still falls within the upper boundary of archaeological dating estimates of
rice phytoliths collected from the lower Yangtze (4).


My comment:
(a) I am in a university library whose libraries subscribe to PNAS. Thus I can read full text online.  General public like you will be able to read only abstract. But that is enough if you continue to read my comments.

(b) wild rice: Oryza rufipogon
(i) California Department of Food and Agriculture.
http://www.cdfa.ca.gov/phpps/pe/AgCommID/page58.htm
(ii) close-up. Federal Noxious Weed Disseminules of the U.S.
http://keys.lucidcentral.org/keys/v3/FNWE2/key/FNW_Grasses/Media/Html/fact_sheets/Oryza_rufipogon.htm
(iii) http://en.wikipedia.org/wiki/Oryza_rufipogon

(c) Oryza sativa
http://en.wikipedia.org/wiki/Oryza_sativa
(has the smallest cereal genome consisting of just 430Mb across 12 chromosomes; Oryza sativa contains two major subspecies: the sticky, short grained japonica or sinica variety, and the non-sticky, long-grained indica variety. Japonica are usually cultivated in dry fields, in temperate East Asia, upland areas of Southeast Asia and high elevations in South Asia, while indica are mainly lowland rices, grown mostly submerged, throughout tropical Asia)

* We can appreciate the different sizes of indica and japonica in photo 2 of
The Basics. Rice Diversity, undated.
http://www.ricediversity.org/thebasics/

* There are more varieties within indica and japonica.
Rice Types. TomThai, June 4, 2008.
http://www.tomthai.com/Foods/E5F46CF9-F804-46CC-99A5-61F5A46E0822.html

Akita komachi rice  秋田(県) こまち 米
koshihikari 越光
http://en.wikipedia.org/wiki/Koshihikari

(d) Rice: Recommended Readings. Economic Research Servie (ERS), US Department of Agriculture (USDA).  
http://www.ers.usda.gov/Briefing/Rice/readings.htm

What are important to the understanding of the PNAS article is (1) and (2) below, both of which indicates China, as well as US, grows indica AND japonica. (The (3) and (4) may be helpful in generalities, from which I extract the critical points. There are no need to read (1) to (4) on your own
.)
(1) Nathan Childs and Amy Burdett, The U.S. Rice Export Market. ERS, USDA, Feb 9, 2001.
http://www.ers.usda.gov/Briefing/Rice/SpecialArticle/USricemarket.pdf

The sidebar in page 49 (or web page 2), titled "The Global Rice Market Is Stratified by Type and Quality," stated:

"There are four types of rice traded globally: indica, japonica, aromatic, and glutinous. Indica rice is the dominant type of rice traded worldwide, accounting for almost 80 percent of global trade. Indica rice cooks dry, separate, and fluffy. It is grown mostly in tropical and sub-tropical areas. U.S. southern long and medium grain rices are considered indica. Japonica rice, which cooks moist and sticky, accounts for more than 10 percent of global trade and is typically grown in temperate climates. Japonica rice has a more rounded grain than indica. California medium grain rice is a japonica.

"Aromatic rices, primarily Thai jasmine and basmati from India and Pakistan, account for almost 10 percent of global trade and sell at a premium to indica and japonica. Aromatic rices are also called fragrant rices. And finally, glutinous rice (or sweet rice), grown mostly in Southeast Asia, accounts for almost all of the remainder. Glutinous rices lose almost all of their shape during cooking and
are typically used in ceremonial dishes and in pastes. Like aromatic rices, they sell at a premium to indica and japonica. The bulk of glutinous rice is grown in Southeast Asia. The United States grows a very small amount of glutinous rice, mostly in California.

"Thailand, Vietnam, China, the United States, and Pakistan are the primary exporters of indica rice.
Argentina, Uruguay, Guyana, Burma, and Surinam export smaller amounts of indica as well. Australia, Egypt, China, the EU and the United States are the primary exporters of japonica rice. Thailand, India, and Pakistan export the bulk of the aromatic rices, with the United States exporting a very small amount. Thailand accounts for most of the glutinous rice traded. In addition, the United States exports a very small amount of glutinous rice, grown mostly in California, to Japan.

(2) James Hansen, Frank Fuller, Frederick Gale, Frederick Crook, Eric Wailes and Michelle Moore,  China's Japonica Rice Market: Growth and Competitiveness. ERS, USDA, Mar 20, 2003.
http://www.ers.usda.gov/Briefing/Rice/SpecialArticle/RCS2002ChinaJaponicaRice.pdf   

Quote from page 32/web page 2:

"In China, japonica rice was traditionally grown and consumed primarily in the northern provinces, while
indica rice was dominant in the south. In 2000, indica rice accounted for about 60 percent of China’s total rice production of 188 million tons (rough rice) and japonica rice about 29 percent, the remaining 11 percent is glutinous rice and some indigenous rice varieties (Crook et al.). Each year, China produces an early, a single, and a late indica crop; a single and late japonica crop in the Yangzi River valley; and a single japonica crop in the north. China is the largest riceproducing country in the world, accounting for a third or more of global production.

"Japonica rice area in China has expanded for the past two decades, growing from 11 percent of total rice area in 1980 to 29 percent by 2000 (Crook et al.). The largest expansion of japonica rice plantings has occurred in the three northeastern provinces, with growth averaging more than 5 percent a year during the 1990s, an increase totaling more than a million hectares. Most of the growth occurred in Heilongjiang province, where japonica rice was the most profitable crop during the 1990s. In the lower Yangzi River valley provinces of Jiangsu, Zhejiang, and Anhui, producers have substituted indica with japonica rice.

(3) Katherine Baldwin and Nathan Child, 2009/10 Rice Year Book. ERS, USDA, December 2010.
http://usda.mannlib.cornell.edu/usda/current/RCS-yearbook/RCS-yearbook-01-05-2011.pdf

(i) Figure 6 "These 6 countries account for more than 85 percent of global rice exports": Thailand  Vietnam > Pakistan > US > India > China

China's export has decreased each year in the period 2008-2010 to ~0.6 million tons (milled basis).

(ii) "These two States [Arkansas and Louisiana] produce almost all the Southern medium/short-grain crop. California growers, who produce more than two-thirds of the U.S. medium/
short-grain crop." page 9
(iii) In 2009 US grew long-grain rice in almost 2.5m acres and medium-short grain in almost 1m acres. Figure 9
(iv) The six rice producing states in US: Arkansas > California > Louisiana > Mississippi > Misouri > Texas   Figure 11
(v) "In 2009/10, the U.S. imported 19.0 million cwt of rice * * * Thailand supplied most of the U.S. rice imports classifi ed by the Census Bureau as medium/short-grain. Nearly all of the medium/short-grain shipments from Thailand were specialty rices. " page 14

* For cwt, see hundredweight
http://en.wikipedia.org/wiki/Hundredweight
(or centum weight (abbreviated cwt); Its British definition is not the same as that used in North America; In U.S. customary units, a (short) hundredweight is defined as 100 lb, which is equal to 45.359237 kg)

(vi) In 2009/10, US exported 550,000 tons (product-weight basis) to Northeast Asia, Figure 20, which is made up of "three Northeast Asian buyers—Japan, South Korea, and Taiwan."

(4) Nathan Childs and Janet Livezey, Rice Backgrounder. ERS, USDA, January 2006.
http://www.ers.usda.gov/Publications/RCS/Dec06/RCS200601/RCS200601.pdf

(i) "The average farm size for rice [almost 400 acres in 2002] is substantially larger than for most
other field crops" Figure 1
(ii) "Arkansas accounts for almost half of U.S. rice planted acreage" Figure 3
(iii) "Classes and Types of Rice
In the United States, rice is referred to by length of grain: long, medium, and short. Long-grain rice, grown almost exclusively in the South, accounts for more than 70 percent of U.S. production. Medium-grain, grown both in California and the South, accounts for more than one-fourth of total U.S. production and forms most of California’s rice crop. California grows more than two-thirds of the U.S. medium-grain
crop. Arkansas accounts for most of the southern medium-grain production. Short-grain rice accounts for 1-2 percent of total U.S. rice production and is grown almost exclusively in California. U.S. long-grain
varieties typically cook dry and separate, while U.S. medium/short-grain varieties are typically moist and clingy." sidebar in page 9
(iv) "More Than Half of the U.S. Rice Crop Is
Marketed Domestically" page 5

"Beer use accounts for about 15 percent of total domestic disappearance" page 6
(v) "Northeast Asia Is the Largest Market for U.S. Medium/Short-Grain Exports." page 8
(vi) "Rice and cotton have the highest per acre operating costs among
major field crops" Figure 10

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