Journal Search Engine
Search Advanced Search Adode Reader(link)
Download PDF Export Citaion korean bibliography PMC previewer
ISSN : 1225-8504(Print)
ISSN : 2287-8165(Online)
Journal of the Korean Society of International Agriculture Vol.34 No.4 pp.298-305

Determinants and Constraints influencing Yam Production in Nigeria

Samuel A. Fasusi, Ji-Min Kim, Sungtaeg Kang
*Department of Crop Science & Biotechnology, Dankook University, Cheonan 31116, Republic of Korea
Corresponding author (Phone) +821035510534 (E-mail)
November 22, 2022 December 7, 2022 December 8, 2022


Yam is an important tuber crop nutritionally, socio-culturally, and an income generator for many Nigerian. This explains its high demand both locally and internationally, causing increased production as Nigeria leads world production with about 45.41 million metric tons annually. The peculiarity of yam production in Nigeria entails lower yield, high cost of production, and post-harvest losses. Yam produced in Nigeria falls far below the potential crop yield, therefore, it is essential to close these yield gaps through the provision of solutions to the different constraints that hamper sustainable yam production. Despite the challenges, there is still insufficient information on the impact of policies, weeds, pests, and diseases which constitute major constraints. Nigerian farmers mostly utilize indigenous cultural approaches to manage yam production. Their goal of production is to produce yam cultivars that are suitable mainly for food products leading to the neglect of other cultivars. Few selected institutions with a yam mandate have been working on improving the production of D. rotundata and D. alata through breeding yam cultivars suitable for consumption and resilient against pests and diseases. However, more extensive studies should focus on breeding programs for yam resilient under drought and flooding, with peculiar physicochemical properties that give unique textual qualities considered in pounded yam and other yam food products. In this review paper, the significance and limitations of yam production in Nigeria and her efforts to achieve sustainable production are extensively studied.

나이지리아 마 생산관련 결정요인과 제한요인

파수시 사무엘 아누오루와포, 김 지민, 강 성택
*단국대학교 생명공학대학 식량생명공학전공



    Yams (Dioscorea spp.) are herbaceous food crops having twine and belong to the family Dioscoreaceae. It is considered the second most important root and tuber crop globally grown behind cassava based on the daily calorie supply and its production (Nweke et al., 1991). Yams are the fourth of the top 10 major crops cultivated in Nigeria, which follows guinea corn, cassava, and maize (Statista, 2019). Yams are described as climber plants that are tuberbearing and can be classified as a monocotyledonous annual or perennial crop with more than 600 species worldwide (IITA, 2009). It is grown on about 5 million hectares in 47 countries in the world mainly within the continent of Africa, Asia, South America, and North America (Acquaah, 2005;Vincent et al., 2015). The West African region contributes about 94.63 percent of global production (FAOSTAT 2022) mostly from Nigeria, Ghana, Benin, Cote D’Ivoire, and Togo.

    In Nigeria, only a few yam species are considered edible and widely cultivated. Nigeria is regarded as the largest producer of yam both in Africa and globally with a production of 45.41 million MT which is 68.4% and 66.9% respectively as seen in Figure 1 (FAOSTAT 2022). It is predominantly grown in Benue, Taraba, and Nasarawa states where it is mostly exported to other countries. Production of yam in Nigeria is across regions with sufficient sunshine, rainfall, and soil fertility to support growth which includes the southern guinea savanna, forest, and derived savanna ecological zones as seen in Figure 3 (Nweke et al., 1991). Due to the ecological requirement of the different cultivars, it possesses the ability to thrive in these different ecological zones. The annual rainfall requirement for yam production is between 1168.4 mm and 2500 mm (Adegbite et al., 2006). The peculiar rainfall duration of lesser than 6 months in the Sahel and Sudan savanna of Nigeria, makes the region not suitable for yam production (Fig. 3). Yam is an important staple crop of Nigerians which supplies about 258 dietary calories per day, therefore, is believed to be key to food security (IITA, 2009). It chiefly supplies carbohydrates plus a good source of essential amino acids, minerals (phosphorus, calcium, and magnesium), and vitamins as food crops (Mudiope et al., 2012). However, in East Asia, yam is cultivated solely for medicine (Kwon et al., 2016).

    There are differences in yam species mostly cultivated in Nigeria and Korea based on their uses and origin. In Korea, grown yams are D. polystachya and D. japonica which are of East Asia origin and important in herbal medicine (Hur et al., 2008;Cao et al., 2021). However, in Nigeria, yams mostly grown are D. alata and D. rotundata from Southeast Asia and West Africa respectively, and important for food while D. alata sometimes is used as herbal medicine (Otegbayo et al., 2005, Sugihara et al., 2020).

    Although Nigeria’s yam production has increased over the years, is yet to attain optimum production as the achieved yield is significantly lower than the potential yield of grown varieties. Most yields from West African countries exceed Nigeria’s yield in farmers’ plots. The average yield in Ghana is 18.22 t/ha, in Benin is 13.76 t/ha while Nigeria produced 7.94 t/ha in 2020 (FAOSTAT 2022). There are varying factors accounting for the yield gap experienced in Nigeria’s yam production.

    This review extensively examines the importance of yam in Nigeria’s food security and identified contributing and limiting factors to optimum production. This will guide further studies on effective management strategies to attain sustainable yam production.

    Cultivation Practices of Yam in Nigeria

    Yam is best cultivated on sandy loam soil that possesses good water-holding ability and organic matter content. The propagation of yam is mostly through yam setts from earlier harvested tubers grown on ridges with mulching to cushion against desiccation and excessive heat. The size of the yam sett affects the overall yield during harvesting. There are two planting dates for yam in Nigeria: Early yam is between November and December, and Late yam is between March and April. Stakes of different sizes are provided to support vegetative growth, for better exposure to sunlight, and to increase tuber yield by over 30% when compared to non-staked yam. Weeding is labor-intensive and done thrice before harvesting. Harvesting is within 6 to 12 months depending on the cultivar. The indicator of maturity before harvesting includes cessation of vine growth, fully flowering plant, and basal leaf color change to yellow. During harvesting, tubers are dug out from the soil with the aid of diggers, hoes, spades, and cutlasses. Yam tubers are most times stored under ambient temperature for a duration of 4-6 months (Sahore et al., 2007) to achieve more profit during sales. A study recommended 300kg/ha of NPK fertilizer at 8-12 weeks after planting for optimum yam production (Law-Ogbomo and Remison, 2009). A pre-emergence herbicide recommended for weed control is atrazine at the active ingredient dose of 2-3 kg/ha (Korieocha, 2014).

    Adoption of Yam as a major crop in Nigeria

    Out of the 10 edible yam types globally grown, six are cultivated in Nigeria. In Nigeria, guinea (white (Dioscorea rotundata) and yellow (Dioscorea cayenensis)) yam and water yam (Dioscorea alata) are widely cultivated. The minorly grown yams are the Aerial (D. bulbifera), sweet yam (D. dumetorum), and lesser (D. esculenta). They all belong to four taxonomic groups which are Enantiophyllum , Opsophyton, Lasiophyton, and Combilium (Lebot and Dulloo, 2021). West Africa is believed to be the origin of D. rotundata before it went through the domestication process that resulted in many landraces within Nigeria (Tamiru et al., 2007). An earlier study identified Nigeria and Togo as countries with the highest genetic diversity of D. dumetorum hence, considered centers of diversity and origin (Sonibare et al., 2010). The guinea yam is believed to emerge from the domestication process of wild yams belonging to the Enantiophllum group.

    Yam production is widely adopted across the middle belt, South-South, South-East, and South-West regions of Nigeria among the Tivs, Efik, Ibibios, Igbos, and Yoruba cultural groups (Obidiegwu and Akpabio, 2017). Farmers are encouraged to produce this crop due to its high demand as the “King of food” in most ethnic groups’ social functions such as traditional ceremonies, marriage, rituals, new yam festival, or burial (Obidiegwu and Akpabio, 2017). It is a source of income with a potential impact on foreign exchange based on income generated from exporting yam worth US$ 27.7 million to the United States in 2011 (Babatunde, 2012). Yam produced in Nigeria is mostly exported to United Arab Emirates, Canada, the United States, and India. Two different profit analysis study of yam production per hectare in Nigeria in 2013 reveals a 202.44 % profit with a gross margin of ₦463,039.88K, and another was ₦450,000 which was US$2,000 equivalent (Simpa and Nmadu 2014;Asala and Ebukiba 2016).

    The sociocultural preference for yam food products and increase in human population, and the size of land devoted to yam production account for the doubled production quantity between 1999 and 2020 (Figure 1).

    Constraints on Yam Production in Nigeria

    Biotic Stress

    The activities of weeds, pathogens, insects, and pests on yam farmland limit average yield. Insect pests and diseases constitute a major constraint to yam production in Nigeria. Every stage of development of yam (from seedling to harvesting or storage) is susceptible to disease infection. Diseases affecting yam production are classified mainly into field and storage diseases. Earlier reports established that about 50% of harvested yam tubers are lost during storage (Onayemi, 1983) due to microbial attacks permitted through earlier wounds before or during harvesting (Amusa et al., 2003). That is, the postharvest losses are due to insect attack, sprouting, respiration, and bacterial and fungal infestation leading to rotting, (Aboagye-Nuamah et al., 2005;Ajayi and Olorundare, 2014). Viruses affecting yam production belong to about 3 genera which include Potyvirus, Cucumovirus, and Badnavirus while others remain unclassified (Amusa et al., 2003;Asala et al., 2012;Diouf et al., 2022). A very high incidence rate and severity are associated with Yam mosaic virus (YMV) across yamgrowing regions of Nigeria. Aphids transmit potyvirus that infects different yam cultivars. Symptom expressions are green spotting, chlorotic spotting, mosaic, vein banding, mottling, curling, and symptomless (in cases of latent infection) (Amusa et al., 2003). Activities of viruses on yam limit its exchange as germplasm internationally (Asala et al., 2012). Prevalent plant parasitic nematode (PPN) in yam-growing regions of Nigeria belongs to about 14 genera. However, Pratylenchus spp, Scutellonema spp, and Meloidogyne spp remain the most widely distributed across Nigeria (Kingsley, 2021). They affect yam both on the field and in storage. They cause root galling, root lesions, and dry, and soft rots depending on the type of PPN. The Xiphinema spp is a typical PPN that acts as a vector of viruses that pose secondary infection in the field. In severe cases of PPN, foliar symptom expression involves early yellowing and leaf senescence cessation of vine growth (Amusa et al., 2003). The most devastating diseases causing agent in storage is the dry rot of yam while the most widely spread disease-causing agent in the yam field is Anthracnose. Anthracnose diseases are mostly caused by Colletotrichum gloeosporiodes (fungus). Rots caused by Aspergillus flavus, Aspergillus oryzae, Aspergillus niger, Fusarium moniliforme, Fusarium oxysporium, and Fusarium culmorum affect yam in storage (Amusa et al., 2003;Ajayi and Olorundare, 2014). They account for a postharvest loss of about 20-60% (Okigbo and Ikediugwu, 2000). This rot can be dry, wet, or soft rot. In Southwest Nigeria, Glomerela angulate causes field anthracnose disease also called ‘scorch disease’. Symptoms include leaf lesions that are small black or dark brown and could be large-scale necrosis or die-back of the stem and withered leaves in severe cases. Concentric leaf spot diseases are caused by Sclerotium rolfsii a folial yam disease with circular leaf spots forming a concentric ring (Amusa, 2001). Bacteria belonging to about 4 genera which include Micrococcus spp, Bacillus spp, Staphylococcus spp, and Enterococcus spp (Ajayi and Olorundare, 2014) affect yam production. Infected yam tubers when pressed ooze out whitish fluid with is unique to wet rot. This wet rot is associated with Erwinia carotovora pv (Amusa and Baiyewu, 1999). Summarily, yam disease agents adversely affect yam production by reducing both the quality and quantity of yam produce and rendering them unappealing to consumers with possible economic loss to farmers.

    Different forms of insect pests such as tuber and leaf beetles, mealy bugs, scale insects, termites, and crickets affect both on the field and in storage (Ogbonna, 2019). They create holes into tubers which enhance the activities of other pathogens such as fungal infestation that results in tuber rots. Grass cutters and bush rats also affect yam both on the field and in storage (Ogbonna, 2019). They dig into heaps to bring out planted yam sett or uproot growing tubers. Parasitic weeds such as Striga hermonthica and other non-parasitic weeds with rapid growth under staking limit yam production. The severity of weed effect on yam production occurs in cases of prolonged weed interference over a period of 3-4 months with a 54-90% yield reduction (Akobundu, 2006).

    Abiotic Stress

    Climate change significantly creates a varying pattern of precipitation and increased temperature across the different agroecology of Nigeria. This poses a great challenge for Nigerian farmers in compensating for the changes as they practice rain-fed farming. There have been frequent occurrences of flooding in yam producing region most especially in North Central which result in massive loss of farmland and displacement of farmers. A series of drought events in Nigeria resulted in the shift of agroecology with the physiological stress of crops grown (Shiru et al., 2020). Nigerian soils are characterized by diminishing soil fertility due to intense farming activities and less supply of fertilizer (Aniekwe and Mbah, 2014). Most of the soil under yam cultivation in the North-central and Southeast regions of Nigeria is found to have reduced Nitrogen, soil organic matter, and cation content which assures drastic yield decline with continuous yam cultivation (Neina, 2021). The record of yam yield over the years shows a decline from 9.4 t/ha in 1988 to 7.94 t/ ha in 2020 (FAOSATAT 2022), mostly attributed to decrease in soil fertility and biotic stress. A decline of at least 10% and 12% in white yam and yellow yam respectively are observed in the subsequent year of production (Neina, 2021). All of these suggests the need for augmentation of nutrient through fertilizer application. A study on the importance of fertilizer application on yam production presented an 80% increase in yield per hectare with NPK fertilizer application at the rate of 300 kg/ha when compared to zero fertilizer application (Law- Ogbomo and Remison, 2009).

    Other Limiting Factor

    Poor government policies such as the removal of government aid on the purchase of fertilizer lead to the inflation of prices which makes it unaffordable to Nigerian farmers (Aniekwe and Mbah, 2014). The frequent armed conflict in Northern Nigeria also militates against sustainable yam production due to threats to life. Agricultural inputs and resources are insufficient to close on yield gap. Most farmers lose a great percentage of harvested yam due to the inability to provide ambient conditions at the recommended storage temperature of about 12°-16 °C during storage. Farming activities in yam farms are purely labor intensive in the absence of farm machinery. The high cost of labor, staking, and improved yam cultivars limit production. Farmers lack access to funds to support farming activities. They recycle earlier harvested tubers which are easily perpetuated by pests and pathogens. Consumer demand for a few selected yam cultivars resulted in massive production of these preferred cultivars with biodiversity loss of other potentially important yam cultivars in Nigeria.

    Yam Breeding and Improvement activities in Nigeria

    The different constraints of yam production enhanced a concerted effort by the International Institute of Tropical Agriculture (IITA) and the National Root Crops Research Institute (NRCRI), Umudike, Nigeria to produce highyielding and resilient varieties. In achieving genetic improvement in yam, several studies were carried out to understand the complexity of the yam genome. This involves the characterization of germplasm and advancement in molecular markers designated in genome analysis. Also, linkage maps were constructed to identify quantitative trait loci in genes conferring resistance to Guinea and water yam against anthracnose and Yam mosaic virus (YMV) (Mignouna et al., 2003). Presently, IITA has about 5,839 germplasm accessions used in the yam improvement program. These germplasms include Nigeria’s 1,881 accessions (1,535 D. rotundata, 239 D. alata, and 40 D. cayenensis and others).

    The institute IITA has extensively selected and bred Guinea yams since the 1970s with more focus on genetically improving D. rotundata and D. alata (Mignouna et al., 2003). The clones and populations of both were developed by IITA and subjected to further evaluation and selection across different agroecological zones of Nigeria. The NRCRI further evaluated the IITA-derived breeding line before the final release of about 21 varieties, some of which are shown in Table 1. Wild yam is regarded as crucial in future breeding, hence conserved. Landrace cultivars that possess resistance against viruses of yam were also identified.

    Summarily, the goal of the breeding activities is to provide yam varieties that have stable and high tuber yield, resilient against pest and diseases, conform with consumers’ preference for tuber characteristics (culinary quality and size), and has a higher dry matter (Mignouna et al., 2007). A study projected at least a 30% yield increase if the improved varieties were adopted, and farmers utilizes sustainable technologies (Nwogha, 2022).

    Future Directions and Conclusion

    Although Nigeria’s yam production is thriving, there is a need to harness its potential to achieve food security. The indigenous practice of Nigerian yam farmers in managing the biotic stress of yam through roughing, timely planting and harvesting, weeding, burning, crop rotation, intercropping, and the use of botanical pesticides such as extracts from trees, wood ashes, and tree bark should be complemented with the adoption of released improved varieties. The build-up of this biotic stress is associated with the recycling of susceptible harvested yam tubers which makes farming unprofitable. The institutes IITA and NRCRI need to breed more improved yam cultivars that are resilient under drought, flooding, and other conditions that are linked with the current severity of climate change impact in Nigeria. Planting of disease-free yam setts assures tuber quality and quantity during harvest. Hence, the certification of planting material through rapid field tests is needed to limit yam infections (Asala et al., 2012). There is no updated information on the losses associated with biotic stress, therefore, the impact of weeds, pests, and diseases on yam production must be studied. Nigeria needs to fully explore more in utilizing active compounds in yam constituents to achieve therapeutic treatment of illnesses just like the Asians. There is a need for further studies on D. batatas and D. japonica grown in Korea for a better understanding of their nutritional benefits to humans and for genetic improvement.

    In conclusion, this review showcases the importance of yam production and its product in Nigeria’s food security with the identification of both determinants and constraints. The socioeconomic relevance of yam in Nigerian society places a high demand on its production. The constant increase in yam production in Nigeria is due to an increase in available farmland dedicated to yam cultivation. Lack of finance, low soil fertility, pest and disease pressure, and high cost of labor and staking remains the major constraint to yam production in Nigeria. To boost productivity, government support should be encouraged through access to loans, provision of storage facilities for yam-producing communities, and subsidies on farm inputs such as fertilizers and planting materials. Nigeria farmers regard yam quality as tubers sustainably generating income and suitable for chief yam products while disregarding other indicators such as nutritional value or bio- mass of other yam parts except for tubers, hence limiting the production of some important yam cultivars (Otegbayo et al.2010). The Nigerian government, however, is supporting yam production through breeding programs for improved varieties, minisett technology development, and training of farmers via on-farm demonstrations on soil nutrient management approaches, and the adoption of released yam varieties.

    적 요

    마(yam)는 나이지리아에서 영양학적 가치 뿐만 아니라 사회 문화적 및 농민의 소득창출원으로 중요한 역할을 하는 덩이줄 기 작물이다. 이러한 국내외적 수요에 따라 현재 나이지리아 는 4,541만톤의 마를 생산하여 세계 마 생산량의 67%를 차지 하는 마의 주요 생산국이다. 본 논문에서는 나이지리아에서 마 생산과정의 문제점과 원인을 구명하고 생산성 증대를 위한 방 안을 제시하고자 한다.

    1. 나이지리아 마 생산과정에서는 낮은 수량, 높은 비용 및 수확 후 관리 미비 등 많은 문제점이 있고, 특히 농가수량과 잠재수량과의 격차도 매우 크다.

    2. 마 생산성 증대와 생산의 지속가능성을 확보하기위한 주 요 제약요인으로 알려진 정책, 병, 충, 잡초 등에 대한 정보가 충분하지 않다.

    3. 국제 열대 농업 연구소(IITA)와 국립 뿌리 작물 연구소 (NRCRI)는 마 유전체의 복잡성을 이해하기 위한 여러 연구가 수행되었으며, 탄저병 및 마 모자이크 바이러스(YMV)에 대한 저항성과 연관된 유전자탐색 연구도 진행중이다.

    4. 현재 나이지리아에서 전통 방식으로 조리되는 마 음식에 적합한 질감을 나타내는 독특한 물리 화학적 특성을 보유하는 D. rotundataD. alata 두 종을 이용한 광범위한 육종연구 가 이루어지고 있다.

    5. 나이지리아 정부는 대출에 대한 접근, 마 생산 지역사회 를 위한 저장 시설 제공, 비료 및 재배 재료와 같은 농장 투 입물에 대한 보조금을 통해 정부 지원을 장려해야 하며 농민 들은 덩이줄기이외의 다른 마의 부분의 영양학적 가치나 생산 량에 대해 관심을 가져야 한다.


    This work was carried out with the support of “Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ0157422022)” Rural Development Administration, Republic of Korea



    The Trend in Yam Production (Million Metric Tonnes) between 1999 and 2020.

    Source: FAO (2022).


    The Trend in Yam Planting Area (10,000 ha) between 1999 and 2020.

    Source: FAO (2022).


    Yam Production region of Nigeria (Stuart et al., 2021).


    Yam (D. rotundata) displayed in Idi-Abere and Bodija markets within Ibadan, Oyo State.


    Information on improved yam varieties in Nigeria.


    1. Aboagye-Nuamah, F. , Offei, S.K. , Cornelius, E.W. , Bancroft, R.D. 2005. Severity of spoilage storage rots of white yam (Dioscorea rotundata Poir.). Annals of Applied Biology. 147:183- 190.
    2. Acquaah, G. 2005. Principles of crop production, Theory, Techniques and Technology. India, Prentice Hall of India private Ltd. 495p.
    3. Ajayi, A.O. , Olorundare, S.D. 2014. Bacterial and fungal species associated with yam (Dioscorea rotundata) rot at Akungba- Akoko, Ondo State of Nigeria. Applied Science Research Journal. 2:12-28.
    4. Akobundu, I.O. 2006. Weed interference and control in white yam (Dioscorea rotundata Poir). Weed Research. 21:267-272.
    5. Amusa, N.A. 2001. Screening of cassava and yam cultivars for resistance to anthracnose using toxic metabolites of Colletotrichum species. Mycopathologia. 150:137-142.
    6. Amusa, N.A. , Adigbite, A.A. , Muhammed, S. , Baiyewu, R.A. 2003. Yam diseases and its management in Nigeria. African Journal of Biotechnology. 2:497-502.
    7. Aniekwe, N.L. , Mbah, B.N. 2014. Growth and yield responses of soybean varieties to different soil fertility management practices In Abakaliki, Southeastern Nigeria. European Journal of Agriculture and Forestry Research. 2:12-31.
    8. Asala, S. , Alegbejo, M.D. , Kashina, B. , Banwo, O.O. , Asiedu, R. , Kumar, P.L. 2012. Distribution and incidence of viruses infecting yam (Dioscorea spp.) in Nigeria. Glob. J. Biotechnol. Biosci. 1:163-167.
    9. Asala, S.W. , Ebukiba, E.S. 2016. Profitability of yam production in Southern Guinea Savanna zone of Nigeria. Net Journal of Agricultural Science. 4:9-14.
    10. Babatunde, J. 2012. Yam Improvement for Income and food Security in West Africa (Y11FS WA) Project. Vanguard April, 2012.
    11. Cao, T. , Sun, J. , Shan, N. , Chen, X. , Wang, P. , Zhu, Q. , Xiao, Y. , Zhang, H. , Zhou, Q. , Huang, Y. 2021. Uncovering the genetic diversity of yams (Dioscorea spp.) in China by combining phenotypic trait and molecular marker analyses. Ecology and evolution. 11:9970-9986.
    12. Diouf, M.B. , Festus, R. , Silva, G. , Guyader, S. , Umber, M. , Seal, S. , Teycheney, P.Y. 2022. Viruses of yams (Dioscorea spp.): current gaps in knowledge and future research directions to improve disease management. Viruses. 14:1884.
    13. FAOSTAT.2022. Food and Agriculture Organization of the United Nations, Rome. Available at: accessed on 01/11/2022.
    14. Hur, G.Y. , Park, H.J. , Kim, H.A. , Ye, Y.M. , Park, H.S. 2008. Identification of Dioscorea batatas (sanyak) allergen as an inhalant and oral allergen. Journal of Korean medical science. 23:72-76.
    15. IITA.2009. IITA Annual report, International Institute of Tropical Agriculture, Ibadan, Nigeria.
    16. Kingsley, E. 2021. Investigation Of Plant-Parasitic Nematodes of Yam In Selected Yam Farms In Two Local Government Areas Of Rivers State. Tropical Agrobiodiversity (TRAB). 2:67-71.
    17. Korieocha, D.S. 2014. Weed control in national root crops research institute Umudike and its recommendation. Res. J. Agric. Environ. Manag. 4:1-4.
    18. Kwon, S.J. , Cho, I.S. , Yoon, J.Y. , Choi, S.K. , Choi, G.S. 2016. First Report of Broad bean wilt virus 2 in Dioscorea opposite Thunb. in Korea. Plant Disease. 100:538-538.
    19. Law-Ogbomo, K.E. , Remison, S.U. 2009. Yield and distribution/ uptake of nutrients of Dioscorea rotundata influenced by NPK fertilizer application. Notulae Botanicae Horti Agrobotanici Cluj-Napoca. 37:165-170.
    20. Lebot, V. , Dulloo, E. 2021. Global strategy for the conservation and use of yam genetic resources. Global Crop Diversity Trust, Bonn, Germany.
    21. Lee, J.H. , Park, C.Y. , Cho, H.J. , Oh, J. , Kim, B.S. , Park, E.H. , Son, C.G , Lee, S.H. 2017. Incidence of Viral Diseases and Occurrence of Three Unreported Viruses in Yams in Korea. Research in Plant Disease. 23:82-87.
    22. Lim, S. , Kim, N.H. , Cho, H.J. , Jeong, H.J. 2019. Enhancement of immune activities of Dioscorea japonica Thunberg in in vivo and ex vivo models. Korean Journal of Food Science and Technology. 51:398-403.
    23. Lim, J.S. , Oh, J. , Yun, H.S. , Lee, J.S. , Hahn, D. , Kim, J.S. 2022. Anti-neuroinflammatory activity of 6, 7-dihydroxy-2, 4-dimethoxy phenanthrene isolated from Dioscorea batatas Decne partly through suppressing the p38 MAPK/NF-κB pathway in BV2 microglial cells. Journal of Ethnopharmacology. 282: 114633.
    24. Manyong, V.M. , Asiedu, R. , Olaniyan, G.O. 2001. Farmers perception of and actions on, resources management constraints in the yam based systems of Western Nigeria In: Akoroda, M.O. and Ngeve, J.M (compilers) Root Crops in the 21st century. Proceeding of the 7th Triennial Symposium of the International society for Tropical Root Crops-African Branch, held at the Centre of International Conferences, Cotonou, Benin, 11-17 October, 1998. pp.156-167.
    25. Mignouna, H.D. , Abang, M.M. , Asiedu, R. 2003. Harnessing modern biotechnology for tropical tuber crop improvement: Yam (Dioscorea spp.) molecular breeding. African Journal of Biotechnology. 2:478-485.
    26. Mignouna, H.D. , Dansi, A. 2003. Yam (Dioscorea spp.) domestication by the Nago and Fon ethnic groups in Benin. Genetic Resources and Crop Evolution. 50:519-528.
    27. Moon, E. , Lee, S.O. , Kang, T.H. , Kim, H.J. , Choi, S.Z. , Son, M.W. , Kim, S.Y. 2014. Dioscorea extract (DA-9801) modulates markers of peripheral neuropathy in type 2 diabetic db/db mice. Biomolecules and Therapeutics. 22:445-452.
    28. Mudiope, J. , Coyne, D.L. , Adipala, E. , Talwana, H.A. 2012. Damage to yam (Dioscorea spp.) by root-knot nematode (Meloidogyne spp.) under field and storage conditions in Uganda. Nematropica. 42:137-145.
    29. Neina, D. 2021. Ecological and edaphic drivers of yam production in West Africa. Applied and Environmental Soil Science. 2021:13
    30. Nweke, F.I. , Ugwu, B.O. , Asadu, C.L.A. , Ay, P. 1991. Production costs in the yam-based cropping systems of southeastern Nigeria. RCMP research monograph. 6:3-42
    31. Nwogha, J.S. 2022. Preliminary verification of the adoption status of some yam (Dioscorea rotundata and Dioscorea alata) varieties in Nigeria using microsatellites markers. African Journal of Biotechnology. 21:198-207.
    32. Obidiegwu, J.E. , Akpabio, E.M. 2017. The geography of yam cultivation in southern Nigeria: Exploring its social meanings and cultural functions. Journal of Ethnic Foods. 4:28-35.
    33. Obidiegwu, J.E. , Lyons, J.B. , Chilaka, C.A. 2020. The Dioscorea Genus (Yam)—An appraisal of nutritional and therapeutic potentials. Foods. 9:1304.
    34. Ogbonna, K.I. 2019. Farmer indigenous experimentation for pest management under yam cultivation farming system in the humid ecological zone of Nigeria. Global Journal of Agricultural Sciences. 18:39-46.
    35. Okigbo, R.N. , Ikediugwu, F.E.O. 2000. Studies on biological control of postharvest rot in yams (Dioscorea spp.) using Trichoderma viride. Journal of Phytopathology. 148:351- 355.
    36. Onayemi, O. 1983. Observation on the dehydration characteristics of different varieties of yam and cocoyam. Abstract 6th symposium of the Int. Soc. For Trops. Peru February, 1983.
    37. Otegbayo, B. , Aina, J. , Sakyi-Dawson, E. , Bokanga, M. , Asiedu, R. 2005. Sensory texture profiling and development of standard rating scales for pounded yam. Journal of texture studies. 36:478-488.
    38. Otegbayo, B.O. , Samuel, F.O. , Kehinde, A.L. , Sangoyomi, T.E. , Okonkwo, C.C. 2010. Perception of food quality in yams among some Nigerian farmers. African Journal of Food Science. 4:541-549.
    39. Sahore, D.A. , Nemlin, G.J. , Kamenan, A. 2007. Changes in nutritional properties of yam (Dioscorea spp.), plantain (Musa spp.) and cassava (Manihot esculenta) during storage. Tropical Science. 47:81-88.
    40. Shiru, M.S. , Shahid, S. , Dewan, A. , Chung, E.S. , Alias, N. , Ahmed, K. , Hassan, Q.K. 2020. Projection of meteorological droughts in Nigeria during growing seasons under climate change scenarios. Scientific reports. 10:1-18.
    41. Sugihara, Y. , Darkwa, K. , Yaegashi, H. , Natsume, S. , Shimizu, M. , Abe, A. , Hirabuchi, A. , Ito, K. , Oikawa, K. , Tamiru- Oli, M. , Ohta, A. , Matsumoto, R. , Agre, P. , De Koeyer, D. , Pachakkil, B. , Yamanaka, S. , Asiedu, R. , Innan, H. , Asfaw, A. , Adebola, P. , Terauchi, R. 2020. Genome analyses reveal the hybrid origin of the staple crop white Guinea yam (Dioscorea rotundata). Proceedings of the National Academy of Sciences. 117:31987-31992.
    42. Simpa, J.O. , Nmadu, J.N. 2014. Profitability of Small-scale Yam Farms in Kogi State, Nigeria. Journal of Applied Agricultural Research. 6:95-105.
    43. Sonibare, M.A. , Asiedu, R. , Albach, D.C. 2010. Genetic diversity of Dioscorea dumetorum (Kunth) Pax using Amplified Fragment Length Polymorphisms (AFLP) and cpDNA. Biochemical Systematics and Ecology. 38:320-334.
    44. Statista.2019. Doris Dokua Sasu, in Ten major crops in Nigeria. Retrieved November 8, 2022.
    45. Stuart, E. , Asfaw, A. , Adebola, P. , Maroya, N. , Edemodu, A. , Adeosun, T. , Asiedu, R. , Almekinders, C. 2021. Yam seed system characteristics in Nigeria: Local practices, preferences, and the implications for seed system interventions. Outlook on Agriculture. 50:455-467.
    46. Tamiru, M. , Becker, H.C. , Maass, B.L. 2007. Genetic diversity in yam germplasm from Ethiopia and their relatedness to the main cultivated Dioscorea species assessed by AFLP markers. Crop Science. 47:1744-1753.
    47. Vincent, C.D. , Nwankwo, E.N. , Ogbonna, C.U. , Onyido, A.E. , Adewuyi, O. 2015. A survey of plant-parasitic nematodes of yam farms in Awka-North local government area, Anambra state, Nigeria. Journal of Applied Biosciences. 95:8950-8957.