Rice, or Oryza sativa as its scientifically known, feeds more than a third of the globe. Yet the majority of rice crops that supply 90 percent of the world come from just two domesticated varieties, japonica and indica.
Despite its importance on global palates and economies, the domestication and origins of rice have remained a mystery. The popular consensus is that japonica, the shorter stickier grain perfect for sushi, has been exclusively cultivated exclusively in northern part of East Asia. In northern parts of East Asia, consisting of Japan, Korea, and northern part of China, current rice production and consumption are japonica with very little exceptional use of indica.
Now, using new data collected samples of ancient, carbonized rice, a team of Japanese and Chinese scientists have successfully determined DNA sequences to make the first comparisons between modern and ancient rice. To do so, they used new techniques to carefully cull chloroplast DNA from ancient rice 900-2,800-years-old, which had been excavated from seven archaeological sites in Japan and Korea.
In the process, they've become among the first research groups to successfully glean DNA information from ancient cereal crop analysis–not an easy feat. Literally, from a single grain of rice, less than 10mg in weight, they were able to glean DNA from typically just a few out of the precious hundreds they were able to sample. These ancient rice samples were compared to a database collected from 216 modern cultivated and wild rice DNA samples from around the world.
They have new findings suggesting that indica rice was historically cultivated in East Asia or imported to East Asia, which go against generally held assumptions. Almost 2,000 years ago, ancient East Asians lived on a wide variety of rice cultivars including indica. The research team has now found, for the first time, the presence of both japonica- and indica-type varieties in the Yayoi period and the middle ages of Japan and the middle part of Korea Peninsula 2000 years ago. Together with the finding of rice variety in Korean Peninsula, the indica variety also contributed to the dietary of people living in archaic East Asia of more than two thousand years ago.
The authors suggest the possibility of cultivation of the indica variety as the ordinary rice variety in the west side of middle of Korean Peninsula more than 2,000 years ago. Another possibility is that indica rice was brought from China, because the area around Lelang in that era was governed by Chinese Han Empire.
"We have shown a decrease in number of the rice cultivar in East Asia from 2,000 years ago to the present," said the authors. "Reduction of genetic diversity by factitious bottleneck is one of the key aspects in domestication process. In addition, development of civilization and technologies has accelerated further reduction of genetic diversity in the modern era. Advanced agricultural technologies including water management, fertilizer and agrochemical enabled farmers cultivating rice fields under different environmental condition to produce varieties having higher value in market. Modernization has promoted sharing of the sense of values, causing homogenization of crop varieties produced."
The study successfully demonstrates the ability of ancient DNA studies to provide new insights into archaic rice diversity and domestication, which otherwise have not been made from DNA evidence solely from modern rice.
Mchele, au Oryza sativa kama inavyojulikana kisayansi, huandalia chakula zaidi ya theluthi moja ya dunia. Kwa kweli, asilimia 90 ya mchele duniani hutoka kwa aina mbili tu za mchele: japonica na indica. Licha ya umuhimu wake kwa vyakula na uchumi wa ulimwengu, utamaduni na asili ya mchele umebaki kuwa fumbo. Japoni, mbegu ya kipekee ya sushi, imekua katika sehemu ya kaskazini mwa Asia. Katika sehemu za kaskazini mwa Asia ya Mashariki, ikiwa ni pamoja na Japan, Korea, na sehemu ya kaskazini ya China, uzalishaji wa sasa wa mchele na matumizi ni japonica na matumizi machache sana ya kipekee ya indica. Kwa kutumia data mpya zilizokusanywa kutoka kwa sampuli za mchele wa kale, timu ya wanasayansi wa Kijapani na Wachina wamefanikiwa kuamua mfululizo wa DNA ili kufanya kulinganisha kwa mara ya kwanza kati ya mchele wa kisasa na wa kale. Kwa kufanya hivyo, walitumia mbinu mpya za kuchimba DNA ya kloroplasti kutoka kwa mchele wa kale wa miaka 900-2,800, ambao ulikuwa umechimbuliwa kutoka maeneo saba ya akiolojia nchini Japan na Korea. Katika mchakato huo, wamekuwa miongoni mwa vikundi vya kwanza vya utafiti kufanikiwa kukusanya habari ya DNA kutoka kwa uchambuzi wa mazao ya nafaka ya kale - sio kazi rahisi. Kwa mfano, katika chembe moja ya mchele, ambayo inazidi uzito wa 10mg, DNA ya watu wachache tu kati ya mamia ya watu waliochukuliwa ni ya kutosha. Kwa mfano, sampuli za mchele wa kale zilipimwa na kuchunguzwa na kuchunguzwa na sampuli za DNA za mchele wa asili na wa kisasa kutoka nchi 216. Utafiti huo unaonyesha kwamba mchele wa Indica ulianza kulimwa Asia Mashariki na kuingizwa Asia Mashariki, lakini kwa kweli haukubaliani na nadharia za kawaida. Karibu miaka 2,000 iliyopita, watu wa Asia ya Mashariki waliishi kwa aina mbalimbali za mchele, kutia ndani mchele wa Indica. Kwa mara ya kwanza, timu ya utafiti imegundua uwepo wa aina zote mbili za japonica na indica katika kipindi cha Yayoi na enzi za kati ya Japan na sehemu ya kati ya Peninsula ya Korea miaka 2000 iliyopita. Pamoja na kupatikana kwa aina ya mchele katika Peninsula ya Korea, aina ya indica pia ilichangia lishe ya watu wanaoishi katika Asia ya Mashariki ya kale zaidi ya miaka elfu mbili iliyopita. "Wanahisiti wanasema kuwa aina ya ""Indica"" ilianza kutumiwa kama mchele wa kawaida katika eneo la magharibi la peninsula ya Korea zaidi ya miaka 2,000 iliyopita." Inawezekana kwamba mchele wa Indica uliletwa kutoka China, kwa sababu eneo la Lelang wakati huo lilitawaliwa na Milki ya Han ya China. "Tumeonyesha kupungua kwa idadi ya aina ya mchele katika Asia Mashariki kuanzia miaka 2,000 iliyopita hadi sasa,"" walisema waandishi." "Kupunguzwa kwa utofauti wa maumbile kwa njia ya udanganyifu ni mojawapo ya mambo muhimu katika mchakato wa kufugwa. Kwa kuongezea, maendeleo ya ustaarabu na teknolojia yameharakisha kupunguzwa zaidi kwa utofauti wa maumbile katika enzi ya kisasa. Teknolojia za kilimo za kisasa, ikiwa ni pamoja na usimamizi wa maji, mbolea na kemikali za kilimo, ziliwawezesha wakulima kulima mashamba ya mchele chini ya hali tofauti za mazingira kuzalisha aina zenye thamani zaidi sokoni. Ujenzi wa kisasa umesababisha kugawanyika kwa maadili, na kusababisha kutofautisha aina za mazao yanayozalishwa". Utafiti huo unaonyesha kwa mafanikio uwezo wa utafiti wa DNA ya kale kutoa ufahamu mpya juu ya utofauti wa mchele wa kale na ufugaji, ambao vinginevyo haukufanywa kutoka kwa ushahidi wa DNA tu kutoka kwa mchele wa kisasa.