US study backs China in the great rice debate
A row has flared after a study by US genome researchers found that the first rice was cultivated in China's Yangtze River valley about 10,000 years ago.
Using modern computer algorithms, new modelling techniques and a pool of more than 600 gene fragments from various wild and domestic rice species, the researchers concluded that wild rice was domesticated at one place, not several; and that place was China, not India.
The study was a collaborative attempt to pin down the exact origin of rice, involving a dozen researchers from New York University's Centre for Genomics and Systems Biology, Stanford University's genetics department, Washington University's biology department and Purdue University's agronomy department.
Their paper, Molecular evidence for a single evolutionary origin of domesticated rice, was funded by the US National Science Foundation, and was published online by the Proceedings of the National Academy of Sciences of the United States of America on Monday.
It has generated fierce debate in China and India. While Chinese researchers embraced the study and called it the 'final judgment', Indian researchers insisted that previous studies had provided stronger evidence that rice originated in India. While Chinese researchers called for the renaming of indica and japonica - the two main subspecies of Asian rice - based on the latest study, Indian researchers insisted there was no need for change.
The US researchers took three key steps. First, they used the newest computer algorithms to analyse datasets examined in previous studies, and found that species previously thought to have originated independently in various locations actually came from one ancestor.
They then resequenced 630 gene fragments from wild and domesticated rice species with new techniques recently applied in human gene analysis. Those results also showed there was only one ancestor.
Finally, they used the 'molecular clock' in rice genes to determine when the first domesticated rice appeared. The time fell between 8,200 and 13,500 years ago, almost exactly when rice domestication began in the Yangtze River valley, according to archaeological excavations.
'As rice was brought in from China to India by traders and migrant farmers, it likely hybridised extensively with local wild rice,' Professor Michael Purugganan, a New York University biologist and one of the authors, was quoted by Sciencedaily.com as saying. 'So domesticated rice that we may have once thought originated in India, actually has its beginnings in China.'
Professor Ding Yanfeng , from Nanjing Agricultural University, said yesterday that the US study had confirmed the mainstream view among mainland rice experts that rice originated in China. 'We have been debating it with our Indian colleagues for decades,' Ding said. 'It's good to have some unbiased opinions from the US.' Mainland researchers had been uncovering evidence of rice's Chinese origin since the early 1950s, Ding said. Some scholars traced the ancient pronunciation of the word 'rice' in various languages, including Hindi, to early Chinese pronunciations such as tao, tu and dau, still widely used in southeastern China.
Excavation sites along the Yantze River such as Hemudu in Yuyao, Zhejiang, provided the earliest evidence of the growing, storage and cooking of rice. Carbon dating shows rice was already the main staple in China more than 8,000 years ago.
The world's academic circles not only ignored those findings but named the two main subspecies of rice indica and japonica - as if rice originated in India and Japan - instead of shien and keng, as proposed by Chinese experts. 'Indica and japonica are scientifically incorrect,' Ding said. 'They are politically misleading. They are the biggest mistake in rice research that we Chinese scientists have been trying to correct for decades but nobody listened.'
Professor Zhu Zhen, deputy director of the Chinese Academy of Sciences' Institute of Genetics, said molecular evidence is the 'final judgment' when evidence from other areas, such as linguistics and archaeology, conflicts. 'Genetic evidence is the most precise and objective evidence.'
But Dr T.K. Adhya, director of the Central Rice Research Institute in Cuttack, India, said it was too early to rule out Indian roots for rice.
Some previous studies, such as one led by Professor Susan McCouch of Cornell University in 2007, suggested that rice was domesticated in the warm and humid plains at the southern foot of Himalayas, Adhya said. 'The study is very good and supported by many scientists,' he said. It was unnecessary to change the existing names for rice subspecies, he said. 'People have already got used to them. People have already named names after them. So why bother?'
Dr Xie Fangming, a senior scientist researching hybrid rice at the International Rice Research Institute at Los Banos, in the Philippines, agreed with Adhya. 'Previous studies have accumulated solid evidence of rice's Himalayan origin,' Xie said. 'One new study may not be sufficient to overthrow the past.'
