Limes, lemons and oranges are taste-giving and nutrition-enriching elements of our diet. It is estimated that there are about one billion trees of the citrus genus on earth. Over 60 different citrus fruits are popular in the world today, all of which are hybrids of the three fruits mentioned below, or hybrids of hybrids, and so on: (1) The large, sweet and spongy-skinned Pomelo ( Citrus maxima ; chakotara in Hindi, bamblimas in Tamil); (2) the tasteless Citron, which is used in traditional medicine ( Citrus medica ; Galgal, matulankam or komatti-matulai ), and (3) the loose-skinned and sweet mandarin orange ( Citrus reticulata , Santra , Kamala orange ) that we associate with Nagpur.
Each citrus variety has some distinguishing feature as a USP: for example, the rare Tahiti orange, a descendent of the Indian Rangpur lime, looks like an orange-colored lemon and tastes like a pineapple.
The first oranges
Where did the citrus originate? Botanist Chozaburo Tanaka was an early proponent of the Indian origin of the citrus. An exhaustive study of the genomes of many citrus varieties concluded that the last common ancestor of all the varieties we see today grew about eight million years ago in what is now Northeast India (overlapping Meghalaya, Assam, Arunachal, Nagaland and Manipur) and adjacent regions of Myanmar and Southwest China (Wu, et al, Nature (2018) 554, 311-316) This region is, famously, one of the world’s richest biodiversity hotspots. A biodiversity hotspot is defined as a region that contains at least 1,500 species of native plants, and has lost at least 70% of its vegetation. The Northeast corner has 25% of India’s forests and a large chunk of its biodiversity. Here you will find tribes such as the Khasi and Garo, and nearly 200 spoken languages. This area is also a rich repository of citrus genomes, with 68 varieties of wild and developed citrus found here today.
The fruit of ghosts
Of special interest is the wild Indian citrus, a progenitor species of citrus that is native to Northeast India (Latin name Citrus indica Tanaka). Some experts believe that it may even be the original member of this group. Our own wild orange has been studied in the Garo hills of Meghalaya, where only scant patches remain (Kalkame Momin et al, International Journal of Minor Fruits, Medicinal and Aromatic Plants (2016) 2, 47-53).
Recent searches, along with detailed molecular comparisons, have led to its rediscovery in the Tamenglong district of Manipur, a thickly forested place with a population density of just 32 per square kilometre (Huidrom Sunitibala and colleagues, Genetic Resources and Crop Evolution , (2022) 69, 545-558). The Manipur team could find three isolated clusters of Citrus indica , the largest of which had 20 trees. High rainfall and high humidity prevails here, with annual temperature extremes of 4 and 31 degrees Celsius.
The Manipuri tribes call it Garuan-thai (cane fruit), but they appear to have neither cultivated nor culturally assimilated this fruit, as has been done by the Khasi and Garo people. The Garo name for the fruit is Memang Narang (ghost fruit), because of its use in their death rituals. Traditional medical uses involve digestive problems and common colds. Villages attentively tend their memang trees.
The fruit itself is small, weighing 25–30 grams, from dark orange to red in colour. The tribes relish the ripe fruit, with its intense sourness. The taste comes from phenolic compounds, which are strong anti-oxidants, and flavonoids (such phenolics and flavonoids are found in fashionable anti-aging skin lotions).
Mankind, however, seems to prefer sweetness, and orange breeders have responded. We Indians, however, are not that averse to sour tastes! We are very fond of the lime ( Citrus aurantifolia Swingle; nimbu,elumichampalam ). India is the world’s leading producer, and our breeders have done very well, with new varieties (Vikram, Premalini, etc.) from agricultural Universities in Parbhani and Akola giving high yields even in semi-arid terrain.
As a result, Citrus indica remains obscure. Its status is severely threatened, it is cultivated in only a few villages, and the genome has not been sequenced.
Reducing the phenolic and flavonoid content in citrus fruit may not all be for the good, as they serve in defending the plants from pathogens. Carefully identifying, preserving the remaining wild varieties of citrus in the Northeast, and studying them in detail would not just provide knowledge. It would help future-proof the oranges and limes that are grown today, aiding in improving disease resistance as well as the health benefits that these wonderful fruits provide.
(The article has been written jointly with Dr. Sushil Chandani, firstname.lastname@example.org, email@example.com)