Domestication of rice (Oryza sativa) based on the current scientific data from archaeological and linguistic is assessed to have started in between 13500 to 8200 years ago at the Yangtze River basin. It first spread to East Asia and thence onwards to all parts of the globe. It is estimated that Oryza sativa consist of about 40,000 landraces or cultivars. The two sub-populations of rice, Oryza sativa indica and Oryza sativa japonica sprang up from the wild rice Oryza rufipogon (Wainu chara) in the Yangtze basin.
There are claims that the japonica sub-population when it reached India developed into the indica sub-population some 4500 years ago after hybridisation with the proto-indica wild rice Oryza nivara. The less common Oryza glaberrina was independently domesticated in Africa about 3000 years ago.
Among all the landraces, there are some which are black and aromatic and due to its rareness, it was available only to the royalty and the nobles and hence such varieties were called forbidden rice.
Some of the popular black rice varieties now are Indonesian black rice, Philippines balatinaw black rice and pirurutong black rice, Thai Jasmine black rice and the Manipuri Chakhao. In Bangladesh, it is known as kalo dhaner chaal. Tamil Nadu has its black rice known as Karuppa Kavuni.
At present in Manipur, there are five common landraces of Chakhao namely Chakhao poireiton, Chakhao amubi, Chakhao angoubi, Chakhao angangbi, and Chakhao pungdol amubi.
However, according to Potsangbam Devakanta, an awardee for his efforts in the conservation of different landraces of rice from Manipur, there were more than 20 landraces of black aromatic rice from both the hills and valley but now most of them are lost though some still continue to survive.
Some of the rarer varieties are Chakhao sempak, Wairi chakhao, Khurkhul chakhao, Kotha chakhao, Wahong chakhao, Pong chakhao, Langphou chakhao, etc.
The landraces were determined based on the morphological characters, including panicle, plant height, aroma, colour, stickiness, etc.
According to Devakanta, Wahong chakhao which is from Wahong village in Ukhrul district is black in colour but with no aroma, but is tasty.
The aroma of Khurkhul chakhao from Khurkhul village in Imphal West is next to Chakhao poireiton and better than chakhao amubi.
In fact, when this writer was a kid, Chakhao amubi was not popular as it lacks aroma vis a vis poireiton. Wairi chakhao grains are small in size and delicious.
According to Poireiton Khunthok, an old manuscript, there was a reference to the cultivation of paddy and to the chakhao and the variety he brought to Manipur was known as Chakhao poireiton, This happened sometime in the 1st century BCE, around 38018 BCE.
It was not known whether paddy cultivation through the slash and burn method was prevailing earlier to his migration and if so other varieties of black aromatic rice was prevalent was unknown.
There is also a question whether the various other landraces of chakhao in Manipur was derived from Chakhao poireiton or whether there are already some growing or whether other also arrived from elsewhere is unknown. These can only be understood through scientific studies, including genetic studies.
The degree of stickiness of rice depends on the quantum of amylopectin, a highly branched starch molecule. Those with higher level of amylopectin are sticky while those with more amylose tend to be less sticky.
The amylose content is the major determinant of rice texture. The amylase : amylopectin ratio determines the hardness or softness of the rice. Higher amylase percentage results in harder or firmer rice while higher amylopectin percentage results in softer or stickiness of the cooked rice.
In storage with time the level of amylopectin slowly decreases and that is the reason why rice of previous years is not as tasty as the freshly harvested one to our palate.
Under the guidance of Prof GA Shantibala of Life Sciences Department, Manipur University, some works have been carried out.
In a paper presented during the national Conference on Indigenous seeds at Central Agricultural University in October 2019 by a student of Prof Shantibala indicated that 2-AP (2-acetyl-1-pyrroline) the main chemical which provides aroma in basmati was not detected in Chakhao. This was quite a surprise as there are reports of its presence in aromatic black rice elsewhere, though it may not be the main chemical for the aroma as there are more than 70 volatile chemicals detected.
In fact there are reports which indicate that about 500 volatile compounds were detected in rice As this chemical is quite labile, there can be error in the process and needs further study. In a paper published in Journal of Advanced Scientific Research, in March 2021 (J Adv Sci Res, 2021,12(1) Suppl 1.01-09) from her team a fairly comprehensive report of their findings on the work on chakhao was presented. The study was carried out in 4 landraces of chakhao namely poireiton, angangba, amubi and angoubi including the assessment of the critical component of amylase, the starch which provides the texture to the cooked product.
Earlier, Asem et al reported the presence of 26 volatiles in poireiton and 11 in angangbi (Intech Open. 2017;125-136). The characters of the different aromatic landraces have to be different as 50% of the landraces are claimed to be from the indica sub-population while the remaining are from a mixture of japonica and indica.
Yang et al reported that the most abundant aromatic compounds present in black aromatic rice are 2-AP, guaiacol, indole and p-xylene (J Agric Food Chem, 2008; 56 (1); 235-240). There are reports that hexanal, (E)-2-nonenal, octanal and heptanal are the major chemicals for the aroma in black rice (Yang et al, J Sci Food Agric, 2010 (15); 2595-2601). This indicates that the characters and the underlying chemical vary greatly among the black aromatic rice and the findings from one area or variety cannot be extrapolated elsewhere. It indicates the complexity of studying life forms. Hence, there is a need for further research on the more popular landrace like poireiton, etc.
Similar work as done in the case of basmati to determine the genetic marker needs to be undertaken. A recessive gene (fgr) on chromosome 8 has been linked to the important trait of the presence of 2-AP. Kovach et al (2020) reported that basmati along with some other fragrant varieties contain an 8 bp deletion and two SNPs (badh1.1) in exon 7 of the BADH2 gene.
The important character of chakhao is its colour, aroma and stickiness and the genetic markers for these characters need to be determined. Further, more concerted research need to be undertaken to assess the volatile compound present in the different landraces of chakhao found in Manipur to determine the base for further studies.
It was a good thing that chakhao has received the GI tag with number 364 in 2020 which makes it a unique item for marketing. One fails to understand why u-morok was not moved for GI tagging as there is no condition that only one state or area can obtain the GI tag for an item if that item is common in more than one state but known by different names. Assam does it for bhoot jalokie while Nagaland got it for Naga Chilli and Manipur should do and get for u-morok and once GI tag number is received, u-morok can become more popular and easily marketable elsewhere.
Export of chakhao, especially the organic brand is ongoing and it is therefore in Manipur’s interest to conduct further study to determine the uniqueness of this landrace through proper and systematic scientific study.
Manipur government may not be able to fund the entire project but it can facilitate fund from the Centre so that a comprehensive project can be undertaken.
It is also important that a comprehensive compilation of all the information available on chakhao is prepared which should inter alia contain the history, tradition and customs, the varieties and its morphological characters besides the scientific findings so that there is a one stop information for those interested and a reference for those who want to know all about chakhao.
(The views expressed are personal)