Global Journal of Science Frontier Research, G: Bio-Tech & Genetics, Volume 22 Issue 2

Physiological and Molecular basis of Dormancy in Yam Tuber: A Way Forward towards Genetic Manipulation of Dormancy in Yam Tubers Jeremiah S. Nwogha α , Abtew G. Wosene σ , Muthurajan Raveendran ρ , Happiness O. Oselebe Ѡ , Jude E. Obidiegwu ¥ & D. Amirtham § Abstract- Yam ( Dioscorea sps ) holds a key position among the staple food crops of Africa and possess better organoleptic properties compared to cassava, potato (within Solanum spp. ) and sweet potato ( Ipomoea batatas (L.) Lam.). Yam tubers are reported to be rich in steroidal C27 saponins and diosgenin which makes it as a crop of choice for the industrial production of pregnenolone-derived steroids. However, prolonged tuber dormancy (spanning between 120 - 180 days after physiological maturity) remains a challenge for yam improvement and production. This poses a serious threat to food security and yam industry. Furthermore, limited research efforts and low investment aggravates the slow progress in yam improvement. Deciphering the physiological and molecular factors involved in the regulation of tuber dormancy in yams will permit genetic manipulation of desired traits in yam. This requires thorough understanding of the physiological and molecular mechanisms regulating tuber dormancy in yam. The present review provides an overview on the basic hormonal biosynthetic/signaling pathways, sugar signaling pathways and the cross talk between them, which provides vital insights into mechanisms regulating yam tuber dormancy. Keywords: yam tuber, dormancy, physiology, molecular, hormones, sugars -metabolism. I. I ntroduction am ( Dioscorea spp ) is one of the oldest recorded crops eaten by human beings in many continents (1). It belongs to the monocotyledonous family, Dioscoreaceae and genus Dioscorea. It is a highly heterozygous polyploid with a basic chromosome number of 10. Most cultivars of the species Dioscorea have varying ploidy levels ranging from tetraploid to octoploid (2). Yam is a multi-species crop which has about 613 known species that produce tubers, bulbils or rhizomes. Of these, about ten are cultivated over larger area and serve as a staple food crop (3). About 50 other species are also eaten as wild-harvested staples famine food, thus this genus occupies a prominent position in global food insecurity combat, (4). Dioscorea rotundata and D cayenesis (both known as Guinnea yam) are the most popular and economically important yams in west and central Africa, where they are indigenous (5). Dioscorea alata has been reported as the most widely distributed species globally, because of its agronomic flexibility and high productive potential (6). Yam holds a great promise in food security, industry, medicine and overall economy in the developing countries (7). Yams are placed at fourth position among the utilized root and tuber crops globally after potatoes ( Solanum spp.), cassava ( Manihot esculenta ) and sweet potatoes ( Ipomoea spp.) and the second in West Africa after cassava (8, 9). It’s potential as a source of food is attributed to its high levels of carbohydrates including fiber, starch and sugar, contributing about 200 dietary calories per person per day to more than 300 million people in the tropics (10). It also provides other nutritional benefits such as proteins, lipids, vitamins and minerals (11). The growing season of yam is long (9 – 11 months) and there is a genetic variation in terms of maturity duration (early, mid and late). In the tropics, the main planting season begins in the month of February (with the planting of dormant tubers) and planting can be done till May. Some farmers plant dormant tubers during December itself. Tubers start sprouting mainly from March to May depending on the storage condition (especially the existing photothermal units), physiological age and genotypes. However, some tubers break dormancy as early as January and this early dormancy breaking is controlled majorly by the physiological age of the tuber and genotype. Harvesting of new tubers starts in the month of August (first harvest season) till December to January of the subsequent year (second/ main harvest season). Whether tubers are Y 1 Year 2022 49 © 2022 Global Journals Global Journal of Science Frontier Research Volume XXII Issue ersion I VII ( G ) Author α : Department of Horticulture and Plant Sciences, College of Agriculture and veterinary medicine, Jimma University, Ethiopia, Departments of Plant Biotechnology and Biochemistry, Centre for Plant Molecular Biology & Biotechnology, Tamil Nadu Agricultural University, Coimbatore, India, Yam Research Programme, National Root Crops Research Institute, Umudike, Nigeria. e-mail: nwoghajerrys@gmail.com Author σ : Department of Horticulture and Plant Sciences, College of Agriculture and veterinary medicine, Jimma University, Ethiopia. Author ρ : Departments of Plant Biotechnology and Biochemistry, Centre for Plant Molecular Biology & Biotechnology, Tamil Nadu Agricultural University, Coimbatore, India. Author Ѡ : Department of Crop Production and Landscape Management, Ebonyi state University, Abakaliki. Nigeria. Author ¥ : Yam Research Programme, National Root Crops Research Institute, Umudike, Nigeria. Author § : Departments of Plant Biotechnology and Biochemistry, Centre for Plant Molecular Biology & Biotechnology, Tamil Nadu Agricultural University, Coimbatore, India.