INTRODUCTION

Nigeria is a country in West Africa situated between Lat 4° 16’ N – 13° 52’ N and Long 2° 49’ E – 14° 37’ E, with an estimated land area of about 92.38 million ha (923,768 km²) (Adeyinka, 2012;Salami et al., 2019). Of this total land area, approximately 71 million ha are categorized as arable land, but only 40 million ha are cultivated (Olowe, 2021).

Forest regions that are endowed with forest plant resources in Nigeria are mostly in the southern region covering about 10% of Nigeria’s land area but it is reported that about 3.5% of the area declines annually due to outright de-reservations and encroachments (Aigbe and Oluku, 2012). Nigeria experiences two distinct seasons throughout the year: the rainy and dry seasons, with plants generally thriving more during the rainy season. The country’s diverse weather and soil types support various plants essential for human existence (Ajayi et al., 2022).

Nigeria is rich in plant bioresources, leading to the cultivation of numerous agronomic, horticultural, forest, and plantation plants due to different agro-climatic, cultural, and socioeconomic factors (Ogbu et al., 2010). Plant Genetic Resources (PGR) are invaluable resources containing the genetic makeup of plants crucial for current and future generations (Singh et al., 2020). Classified into various types, including weedy types, landraces, obsolete cultivars, wild relatives, breeding lines and genetic stocks, modern cultivars, indigenous and exotic species (Oluwaseyi, 2017). They provide a gene pool for engineering resistant and improved varieties during crop improvement programs.

Common plant types found in Nigeria include food crops (cassava, yam, maize, cowpea), cash crops (cocoa, kolanut, rubber, oil palm, cotton), tree plants (Albizia spp, Antiaris africana, Cederella odorata), fruits (pineapple, guava, pawpaw, banana, orange, mango), medicinal plants (Azadirachta indica, Khaya senegalensis, Vernonia amygdalina), ornamental plants (Mexican sunflower, water hyacinth, Chinese hibiscus, pride of Barbados), and forage plants (Combretum aculeatum, Acacia clavigera) (Dukku, 2013;Ekpete, 2013;Fawole and Oladele, 2007;Olamide, 2015;Onilude et al., 2020).

Nigeria is endowed with an abundance of PGR important as food sources, with aesthetic, pharmaceuticals, and economic value, and genetic stock for improved varieties. Currently, a total of 13,839 accessions from 45 crops, including approximately 205 wild relatives and more than 189 species considered threatened have been recorded. This loss of PGR and biodiversity has become a serious challenge lately (Ajiboye and Atoyebi, 2020). In classifying the threatened species in Nigeria, about eighteen (18) and sixteen (16) were categorized as endangered and critically endangered, respectively (Isichei, 2010). Genetic erosion has also occurred due to events of crop domestication and new crop variety’s introduction over the years (Onwe et al., 2023). Many of Nigeria’s indigenous crops have suffered under exploitation and less-priority conservation and are yet to be extensively developed to a commercial scale (Onwe et al., 2023).

The severity of climate change in recent times is accountable for the shift in Nigeria’s ecological zones (Otitoju, 2013), impacting water and soil resources significantly (Fasusi et al., 2022a). An observable effect of climate change is the measurable drop in the volume of Nigeria’s Lake Chad water within the last 30 years (Tologbonse et al., 2011). Generally, urbanization, deforestation, climate change, bushfires, exponential population growth, overgrazing, and environmental pollution are key factors contributing to plant genetic erosion (Ruas et al., 2022). The massive loss of forest resources in rural settlements is linked to the reliance of dwellers on wood for fuel or cooking (Abanikannda and Dantani, 2021;Bankole et al., 2024). The two main classes of forest resources are non-timber and timber forest resources (Table 1). Soft and hardwood trees are essential for furniture, plywood, cooking, textiles, and paper, and belong to the timber forest product. However, forest products that are grown for their plant material (flower, fibers, and creeper), animal products (silk, and honey), food and food additives (wild fruits, spices), and plant derivatives (rattan, raffia, or bamboo) belong to non-timber forest resources (Agbogidi, 2010).

The Nigerian government, private individuals, universities, and different funding bodies have contributed immensely to preventing plant genetic erosion in Nigeria (Osawaru et al., 2022). The government has established various plant-based research institutes to collect and conserve different plant types within the country. Some funding bodies have supported Nigerian farmers by establishing community seed banks to ensure the effective conservation of PGR and guarantee food security. For instance, the Biodiversity Education and Resource Center (BERC) in Abuja, Nigeria, implemented a small grants project (SGP) of about $48,000 between 2018 and 2020, aiding in community seed banking involving seeds of crops such as cowpea, sorghum, millet, sesame, and tomato for biodiversity conservation (BERC, 2021). Additionally, the Islamic Development Bank, in partnership with the Kano State Agropastoral Development Project (KSADP), supported rice community-based seed multiplication in 2022. This project, established in Kano state, aimed to assist farmers with improved rice seed resilience against disease and pests, resulting in twice the previous year’s yield -4 Mt/ha to 7.8 Mt/ha (Sasakawa Africa Association, 2023).

Several national legislations related to plant conservation have been enacted in Nigeria, including the Forestry Ordinance (1937), Environmental Impact Assessment (1992), Federal Environmental Protection Agency FEPA (1992), National Parks Act (1999), and National Environmental Standards and Regulations Enforcement Agency NESREA Act (2006) (Osawaru et al., 2022).

This review article focuses on examining the status of available PGR in Nigeria, conservation strategies adopted by plant-based institutes, and efforts devoted to preventing the extinction of PGR. The study aims to provide up-to-date information guiding future studies on sustaining PGR in Nigeria.

DETERMINANT FACTORS AFFECTING NIGERIA’S PLANT DIVERSITY

In Nigeria, the three main factors that affect plant diversity include:

Climate Change

There has been a change in weather patterns in Nigeria over an extended period, which is linked to alterations in land and ocean surfaces (Oluwaseyi, 2017). The severity of climate change is closely tied to certain human activities, such as deforestation, fossil fuel burning, transportation, and industries, leading to an increased concentration of greenhouse gases (carbon dioxide (CO₂), nitrous oxide (NO₂), methane (CH₄)) (Mousavi et al., 2023). This has resulted in elevated temperatures, extremes in precipitation (including drought and flooding), and the emergence of new plant diseases and insect pests (Omolara and Adekunle, 2021). Collectively, these factors significantly impact plant physiology and survival.

Plant cultivation in Nigeria is predominantly rain-fed farming (Fasusi et al., 2022b), amplifying the impact of climate change, particularly under drought conditions. The most destructive consequence of climate change in Nigeria is flooding, caused by the increased volume of water bodies overflowing onto dry land. The persistent flooding incidents from 1980 to 2022 have led to human displacement and the loss of farmlands (Oluwaseyi, 2017). In 2022 alone, approximately 34 out of Nigeria’s 36 states experienced flooding, resulting in soaring food costs due to extensive farmland losses (Ladan and Mayaki, 2023). The Olam Rice farm in Nasarawa state, for instance, suffered significant losses from the 2022 flooding, affecting over 4500 hectares of rice farmland (Ekpali, 2023).

Climate change induces a shift in agroecological zones across Nigeria, directly impacting climatic and edaphic factors (Pareek, 2017). Consequently, it poses a substantial threat to plant distribution and abundance in the country. Aside from this, climate change severity supports the survival and abundance of aphids and other insects with a declining population of natural enemies (Fasusi et al., 2024;Thomson et al., 2010).

Agroecological zones

Nigeria is distinctly composed of various agroecologies that influence the types of plants found in different regions. The forest zone constitutes approximately 14% of the land area, while the savanna zone covers roughly 86% of the land area. There are seven (7) agroecological zones in Nigeria, as illustrated in Figure 1 (Amusa et al., 2014). The specifics of each agroecological zone provide insights into the possible plant types that thrive in these areas, as outlined in Table 2. Moving from the southern to the northern region, there is a gradual reduction in both rainfall volume and duration (Oguntunde et al., 2011), leading to a corresponding decrease in plant diversity. The humid forest agroecological zone stands out as the richest zone, boasting diverse plant types attributed to the ample rainfall in the area.

Human Factor

The exponential population growth in Nigeria has exerted considerable pressure on available land, resulting in the displacement of natural plant habitats or forests to make way for human settlement. Comparing Nigeria’s current population of 218 million people to the projected 270 million by 2030 (Oluwatayo and Opoko, 2014), there will be an inevitable and unsustainable use of PGR, posing a threat to the country’s food security.

Numerous deforestation activities have contributed to the extinction of forest resources, leaving the soil vulnerable to flooding and erosion. The demand for timber resources, particularly mahoganies, Afara (Terminalia superba), and Opepe (Nauclea diderrichii) for furniture, paper, and more, has fueled illegal deforestation in Nigeria without adequate replanting (Osawaru et al., 2013). The high rural-to-urban migration of Nigerian youths has resulted in a significant decline in the cultivation of common landraces (wild cultivars), leading to their gradual extinction (Horrigan et al., 2002). Key farmers responsible for the continuous cultivation of these landraces in rural areas are aging and passing away without adequate replacement.

Moreover, the substantial number of nomadic herders has contributed to overgrazing by large herds of cattle, exposing the soil to erosion (Ofuoku, 2010). Indiscriminate bush burning further accelerates the loss of forest resources, with additional damage to soil texture, fertility, and soil organisms (Numbere and Obanye, 2023).

ACTIVITIES OF AGRICULTURAL INSTITUTE

The National Center for Genetic Resources and Biotechnology (NACGRAB) serves as the national focal point for PGR in Nigeria, established under Degree 33 of 1987 (now an Act of Parliament, 2016). NACGRAB oversees the operations of the National Committee on Naming, Registration, and Release of crop cultivars, breeds of livestock, and fisheries. Its broad range of activities encompasses the collection, preservation, stock inventory, viability monitoring, evaluation, and characterization of plant germplasm.

In collaboration with other government-established National Agricultural Research Institutes (NARIs), NACGRAB engages in the exchange of germplasm for research and the development of elite varieties. International partnerships are equally integral, with material exchanges involving organizations such as ICRISAT, ICARDA, and CMMYT. Each NARI specializes in improving specific mandate crops, as outlined in Table 3, and the organizational structure of PGR management in Nigeria is illustrated in Fig. 2.

NACGRAB boasts state-of-the-art facilities, including a germplasm extract room, threshing room, germination/ viability room, and processing equipment (Borokini et al., 2010). For effective seed conservation, NACGRAB maintains two storage rooms equipped with inbuilt dehumidifiers: a short-term storage room (15 °C and 30% RH) and a long-term storage room (-20 °C and 15% RH) (Bako, 2019). Alternative backups, in the form of two large deep freezers, ensure the safety of conserved germplasm in NACGRAB’s seed gene bank. Covering 12 hectares of land, NACGRAB’s collection combines in-situ and ex-situ collections, conserving over 3000 plant species (Ajiboye and Atoyebi, 2020).

Although NACGRAB has 13,839 accessions listed in its inventories, only 10,611 accessions are available in its baselines, possibly due to the loss of predominantly landrace accessions in field seed banks (Table 4). The documentation process assigns each plant germplasm a passport number, including various data from its characterization and evaluation. This documentation incorporates both breeders’ records and indigenous records. Different national programs, supported by NARIs, are established to characterize and evaluate plant germplasm. Information on the seed germplasm stored in the IITA seed genebank is accessible on the provided platform (https://www.genesys- pgr.org/), though there is limited information available on NARIs’ activities and their available PGRs, as outlined in Table 5. Notably, all these NARIs depend on the IITA and NACGRAB seed gene banks. The establishment of the Forestry Research Institute of Nigeria (FRIN) in 1954 fostered research that centered on the identification of forest species composition, regeneration, and allocation to farmers within Southern Nigeria (Erakhrumen, 2007).

CONSERVATION AND UTILIZATION OF PGR IN NIGERIA

The primary purpose of conserving PGR is to collect and preserve plant adaptive gene complexes for current and future use. There are two main approaches to PGR conservation: in-situ and ex-situ. In-situ conservation involves preserving PGR in their natural habitat, fostering the evolutionary process with minimal human interference (Bako, 2019;Salgotra and Chauhan, 2023). This approach allows for the conservation of wild plant species, particularly forest resources, and locally developed landraces. It utilizes forest reserves, parks, and natural reserves, often under the jurisdiction of the forest management ministry. Nigeria, with approximately 27 game reserves, strict nature reserves (SNRs), national parks, and 56 forest reserves, endeavors to achieve in-situ conservation (Bako, 2019). However, challenges such as encroachment and resource loss have limited the success of in-situ collections in Nigeria.

Ex-situ conservation, on the other hand, involves preserving PGR outside of their natural habitat. Field gene banks are deliberately meant to conserve seed propagated vegetatively and recalcitrant seeds (Onwe et al., 2023). This approach employs techniques such as greenhouses, seed gene banks, cryopreservation, and plant tissue cultures to secure endangered PGR and make valuable genetic resources available (Salgotra and Chauhan, 2023). Notably, the activities of most crop-based institutes in Nigeria, including National Agricultural Research Institutes (NARIs) and the National Center for Genetic Resources and Biotechnology (NACGRAB), primarily focus on ex-situ conservation with activities around three (3) decades now. In Nigeria, ex-situ conservation has demonstrated more success in preserving PGR compared to in-situ conservation.

The conservation of PGR in Nigeria is needed to adequately provide genetic material for all breeding studies that encourage climate-resilient crop development. This guarantees food security as better-performing plants under severe climate change are produced. This PGR serves as a vital source of food and oil for humans, fodder for animals, and contributes to the aesthetic value of landscapes and insect pollination (Malik and Singh, 2006). Additionally, PGR plays a role in providing condiments and pharmaceutical products (e.g., Parkia biglobosa), timber for furniture (e.g., Khaya grandifoliola), and non-timber forest products like chewing sticks and rattan (Dawson et al., 2014). Furthermore, they serve as raw materials for agro-allied industries, offering economic benefits by generating income, supporting trade, and creating employment opportunities.

CHALLENGES FACING PGR MANAGEMENT IN NIGERIA

Despite various efforts to sustain PGR in Nigeria, effective management has proven challenging due to several reasons. One prominent issue is the underfunding or inadequate budget allocation for PGR conservation (Nchuchuwe et al., 2012), negatively impacting overall performance. Nigeria faces challenges such as unreliable power supply and high electricity costs, which, in turn, affect the efficient functioning of seed genebanks.

Moreover, the scarcity of state-of-the-art seed genebanks or the inability to replace faulty equipment’s serviceable spare parts poses a significant hurdle. Negligence towards indigenous landraces, driven by farmers’ preferences for improved cultivars, is another contributing factor. Outdated information on PGR is a consequence of insufficient characterization and evaluation of available germplasm. In addressing these challenges, there is a pressing need to establish more ex-situ field collections in the different agro-ecological zones.

Furthermore, the effectiveness of PGR conservation is hindered by unreviewed national laws, decrees, or legislation. The absence of updated legal frameworks supporting PGR conservation allows more offenders to go unpunished, exacerbating issues, particularly with the depletion of forest resources. Addressing these challenges requires a holistic approach, including increased funding, improved infrastructure, enhanced characterization and evaluation processes, and the establishment of comprehensive legal frameworks.

FUTURE DIRECTION AND CONCLUSION

A pragmatic approach needed to conserve PGR in Nigeria is through the establishment of dedicated agencies, as presently designated agencies like the National Environmental Standards and Regulations Enforcement Agency (NESREA) are engaged in multiple obligations that render them ineffective. Also, the Nigerian government needs to revisit the Endangered Species Act (1985), the National Crop Varieties and Livestock Breeds Act (1987), the National Agricultural Seed Act (1992), the National Parks Decree (1999), Biodiversity Conservation laws, the National Biodiversity Strategy and Action plan (2016-2020), and the plant variety protection Act (2021) to suit today need. This involves enacting and implementing all these legal standards to protect endangered plant species, forest reserves, and botanical gardens from unauthorized operations. Hence, the prosecution of all offenders who have encroached into reserve areas is a deterrence to future offenders. Presently, Nigeria is yet to fully tap into the potential of biotechnological approaches in plant biodiversity conservation, hence, the need to harness the tools now with anticipation of successful sustenance of PGR in the future. A comprehensive survey and inventory of PGR across Nigeria are imperative to obtain an accurate estimate of plant species diversity and ensure up-to-date information. Efforts should be directed toward improving the documentation of PGRs and making this information readily available. Encouraging the sustainable cultivation of underutilized crops or plant species is crucial, and granting farmers in local communities easy access to these PGRs is equally important. Despite their less economic importance, more of Nigeria’s indigenous crops should be incorporated into the mandate crops of different institutions. This will significantly increase their values, use, and conservation. Promoting public awareness of the significance of PGR in Nigeria is essential through sensitization programs and introduction into the curriculum of Nigerian students. Government encouragement through adequate funding of PGR projects should upgrade available infrastructure for PGR conservation. This involves upgrading the genebank of NACGRAB to be well equipped with a regulated environmental condition. Environmental changes contribute to genetic erosion leading to the extinction and scarcity of some PGR, highlighting the urgency of conservation efforts.

The diverse plant-based research institutes in Nigeria play a pivotal role in the collection, characterization, evaluation, exploration, and conservation of PGR. These plant accessions are safely duplicated through the exchange of germplasm between the National Center for Genetic Resources and Biotechnology (NACGRAB) and global crop diversity trusts. The challenge of grossly inadequate information on Nigeria’s PGR hampers effective conservation. Recognizing the critical role of PGR in sustainable agriculture and food security is important. Therefore, concerted efforts should be made to address all challenges and ensure the conservation and responsible use of PGR for the benefit of now and future generations

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