Underutilized crops Unlike modern agricultural practices targeting fewer crops, the people of ancient civilization have developed a remarkable diversity of foods to uphold the principles of biodiversity for fulfilling their daily requirements as well as to counteract the weather vagaries (Padulosi et al., 2019). With powerful wisdom and inherited knowledge, people during the early date of civilization have domesticated thousands of plants and animals species in spite of their dependence on food through the “Gathering and Hunting” system (Heywood, 2013). Before the onset of the industrial revolution, people of the particular region make the best usages of the local resources to fulfill their daily requirements. The reliance and endurance on locally available ingredients resulted in the creation of a vast collection of plant germplasm having therapeutic values in addition to basic nutritional qualities that are deeply rooted to local territories and culture (Padulosi et al., 2019). However, the modern agricultural practices narrowed down the diversity of crops leading to the development of risk on food security (Frison et al., 2011; Beddington et al., 2012). It results into underestimating the importance of biodiversity followed by neglecting the crops possessing significance from nutritional and therapeutic values. Nevertheless, the underutilized plant spreads across all food groups including the Dioscorea spp. (Ikiriza et al., 2019). Owing to their potentiality to grow and produce under marginal conditions (rainfed, slopping land, poor soil, low inputs, etc), the Dioscorea spp. offers the opportunity for empowering and safeguarding food security of the most vulnerable community of the society (Padulosi et al., 2019).
Dioscorea spp. Dioscorea spp. (‘Kath aloo’ in Assam, India, ‘Pesta aloo’ or ‘Mete aloo’in Bangladesh, ‘Guinea yam’ in Africa), is one of the most important tuber crops in the world. It is an herbaceous plant with creeping and climbing vines and it comes under monocotyledonous Dioscoreaceae family (Burkill, 1960). With approximately 644 species, it is widely distributed in the tropical and temperate regions of Asia, Africa and America (Agbor-Egbe and Treche, 1995). It is one of the most important food crops since time immoral in several parts of the world because of its rich nutritional characteristics coupled with for traditional medicines as anticancer, anti-inflammatory, antifungal, anti-rheumatism, hypoglycaemic, estrogenic, androgenic, contraceptives, gastropathy protective, antifungal, immunostimulant etc (Kumar et al., 2017). Recently, the global interest for promotion and conservation of Dioscorea spp. has increased several folds because of emerging challenges of the century i.e. ever-increasing population pressure, food security, climate change, fast depletion of natural resources, increasing input cost of modern agricultural practices, and finally the nutraceutical value of the particular plant (Shajeela et al., 2011). According to the available reports, Dioscorea rotundata thought to be the first species that has been domesticated around 5000 BC in West Africa (Andres et al., 2017). The most economically important species under this genus is Dioscorea alata that is originated from Southeast Asia; possibly Myanmar and Thailand (Orkwor et al., 1998). Presently, the particular species of Dioscorea is spread across Malaysia, Indonesia, Philippines, Brazil, South America, Central America, Papua New Guinea, South Pacific Islands etc (Kumar et al., 2017). Air potato i.e. Dioscorea bulbifera is native to South Asia and is distributed among several countries namely Bangladesh, India, China, Cambodia, Indonesia, Java, Japan, Laos, Malaysia, Nepal, Pakistan, Sri Lanka, Thailand, Taiwan, Vietnam, Ghana, Gabon, Congo, Chad, Cameroon, Nigeria, Senegal, Sudan, Zimbabwe, USA, Mexico, Cuba, Costa Rica, Jamaica, Nicaragua, Brazil, Ecuador, Peru, Venezuela, Australia etc. The other high-yielding species is Dioscorea pentaphylla, a native of tropical Asia (Ayensu and Coursey, 1972). The particular species is found in India, Bangladesh, North America and other tropical Asian nations.
By virtue of its climbing nature, it could reach up to the height of 10 m or above depending upon the height of the supporting trees and shrubs. The twinning direction of the plant may be clockwise or anti-clockwise. Rootstock are rhizomatous or tuberous (Lacaille-Dubois, 2002). Branching may be present or absent on the Stems. Leaves of the Dioscorea spp. are alternate or opposite and with or without pointed tips. Major veins are aroused from the base of the leaves and become curved aligning with the leaf shape. The flowers of Dioscorea spp. are small with green or greenish-grey or greenish-yellow in colour. These are unisexual (dioecious plants) and originate from leaf axils (Sautour et al., 2007). The number of flowers may reach as high as 15 to 20 or more on a single spike. The fruits of Dioscorea spp. is popularly known as bulbil and very rich in nutraceuticals of immense significance (Kuete et al., 2012). It routinely originates from the stem as a single or conjugate form with different shapes (round, oval, irregular or elongate). Among all the members of the Dioscoreaceae family, Dioscorea bulbifera is thought to be the most potential owing to its production of bulbils rich in phytochemicals active against piles, dysentery, syphilis, ulcers, cough, leprosy, diabetes, asthma and cancer (Ikiriza et al., 2019). The day length influences the formation of bulbils and shorter the length, bulbil production speeds up (Kumar et al., 2017). The root system of Dioscorea spp. is shallow, fibrous, and it may or may not be anchor type. It concentrates within the top layer of the soil (Onwueme, 1978). Tubers are of different shapes, sizes and colour.