Natural Sciences
Emergence of a Viral Disease Epidemic of Sweet potato in Eastern Africa is Imminent – Plant virologists warn
When COVID-19 emerged in 2019, it first remained temporarily localized as an epidemic in Huan China until it broke Chinese national and Asian continental borders attaining a global pandemic status. With COVID-19 and other epidemics and/or pandemics of humans and livestock, it is easier to explain the obvious impact on humans and/or livestock.
What about virus epidemics and pandemics that affect plants?
Virus epidemics and pandemics that affect plants cause significant disruptions in food production. In fact, the emergence and re-emergence of extremely dangerous plant viruses is the major pain to the 21st century agriculture and sustainable food production.
Viral diseases of plants lead to complex outcomes of food shortages, economic meltdown and loss of lives especially when the affected crop plants are central to the economics and livelihoods of the people. Think of what would happen if an epidemic caused significant effect or eliminated crops like maize, banana, cassava or sweetpotato from sub-Saharan Africa.
Most viruses affecting livestock and humans are spread and transmitted by means of physical contact between hosts. Furthermore, human and livestock hosts are mobile. On the other hand, plants do not move and must thus depend on other agents (vectors) for the spread of viruses between hosts. Consequently, over 98% of plant viruses are transmitted by vectors. These vectors may include arthropods (especially insects), nematodes, fungi, and parasitic plants. In plants, a virus disease epidemic becomes optimized by the ability of vectors facilitating fast spread of the virus in an agro-ecosystem.
New study predicts emergence of disease epidemic in sweetpotato
A new study led by Prof. Arthur Tugume at the Department of Plant Sciences, Microbiology and Biotechnology in the College of Natural Sciences at Makerere University predicts potential of emergence of a new disease epidemic in sweetpotato.
The study recognizes that by default, viruses are not constrained to perpetually occupy a single ecological niche. This is because viruses have inherent genetic and evolutionary abilities that enable their acquisition of better fitness to always expand their host and geographical ranges.
While viruses enjoy such fitness advantages in nature, the current study points out unique examples where some viruses in eastern Africa behave awkwardly. These viruses first hid under the guise of being less important and seemingly of no impact in cropping systems, and all of a sudden hell broke loose and the entire farming system was caught unaware.
The study titled; “Endemism and reemergence potential of the ipomovirus Sweetpotato mild mottle virus (family Potyviridae) in Eastern Africa: half a century of mystery” shows that a virus, named Sweetpotato mild mottle virus (SPMMV) was first detected in eastern Africa in the 1970’s. SPMMV is currently the third most prevalent virus of sweepotato in the region and is most destructive in mixed infections with other viruses. Very strangely, SPMMV is geographically restricted to eastern Africa (confirmed only in Uganda, Kenya and Tanzania). This sharply contradicts other known sweetpotato viruses that occur globally wherever sweetpotato is grown.
According to Dr. Deusdedith Mbanzibwa a co-author and Head of Disease Control Unit at Tanzanian Agricultural Research Institute, “it is a half-century-old mystery how SPMMV remains localized in East Africa while other viruses on sweetpotato show a global incidence.” Dr. Mbanzibwa adds, “it is important we generate basic information on this virus as soon as possible such that immediately an epidemic explodes we can counter-it based on the information we have as opposed to being caught unaware of the destructive effects of an epidemic.”
Why should we be concerned about outbreak of an epidemic on sweetpotato?
Plant disease epidemics cause a breakdown in food production and availability in communities that depend on the affected plants as food staples. If sweetpotato production breaks down, it directly translates into limited food supplies in local communities that depend on it for food.
According to Dr. Titus Alicai, a senior virologist and co-author based at the National Crops Resources Research Institute (NaCRRI), Namulonge Uganda, “between the 1980’s-1990’s, a devastating viral pandemic (cassava mosaic disease, CMD) destroyed cassava cropping systems in eastern Africa. As a result, dozens of lives were lost because many communities solely depended on cassava for food and income”. Although these viruses had been detected in the region as early as 1800’s, it was not until the 1980s that destructive effects of the disease became apparent.
Dr. Alicai adds that, “when cassava got destroyed by CMD, sweetpotato became an immediate alternative to millions of hungry people, but now sweetpotato is also burdened with diseases arising from viruses.” Despite heavy investments in disease control in cassava, the CMD pandemic is not completely controlled.
Why is eastern Africa important with respect to emergence of plant viruses?
According to this study, SPMMV is not the first unique virus to emerge or reemerge in eastern Africa. An earlier study by Prof. Tugume and colleagues published in 2010 in Molecular Ecology showed that East Africa is a hotspot for the evolutionary diversification of yet another virus in sweetpotato, named Sweetpotato feathery mottle virus (SPFMV).
Many studies show this region as the home of epidemics in rice caused by Rice yellow mottle virus (RYMV). Highly lethal strains of Cassava mosaic geminiviruses (CMGs) causing CMD initiated this epidemic from eastern Africa. Unique strains of Sweetpotato chlorotic stunt virus (SPCSV) are incident in eastern Africa. SPCSV is unique because it almost indiscriminately enhances the viral concentrations of other co-infecting viruses in sweetpotato. The list of damaging plant viruses or their strains that have emerged from eastern African region is long and cannot not be exhausted here.
Biologists studying diversity of plants and animals have also coded eastern Africa as a home of the “hottest hotspot of biodiversity” of endemic land plants and animals located in Eastern Arc Mountains of Kenya and Tanzania. The features of eastern African ecosystem that incite virus epidemics in plants are not fully known. However, it is suspected that the microclimatic changes as modulated by the Indian Ocean dipole could be one of the drivers of virus emergence and reemergence in the region.
Emergence of SPMMV in sweetpotato closely resemble that of viruses in cassava
The current study specifically compared SPMMV with two viruses infecting cassava: cassava brown streak virus, and Ugandan cassava brown streak virus, collectively called cassava brown streak ipomoviruses (CBSIs).
CBSIs first appeared in the 1930’s in coastal east Africa but went completely silent for about 70 years and then suddenly re-emerged in late 1990’s-mid 2000’s to what is today the single largest threat to cassava production in Africa. CBSIs cause a disease called “cassava brown streak disease” (CBSD). Between 1930’s-1990’s, the CBSIs were able to “amass ability” to cause untold suffering of cassava cropping from 2000’s to-date.
Similarly, since the 1970’s when SPMMV was first reported in the region, the virus has been “amassing an ability” to cause more disease in sweetpotato. This is implied directly by evidence of positive selection found in its genes. Positive selection refers to “survival for the fittest” in Charles Darwin’s terms to mean that, individual virus particles in the SPMMV population are becoming more and more highly efficient in causing disease. Today, half a century later, one can argue that it is about time that the SPMMV will incite a new disease.
Note that both SPMMV and CBSIs belong to the same taxonomic grouping of plant viruses in a genus called “Ipomovirus”, and family called “Potyviridae” which is the largest family of plant viruses with RNA genomes. Hence, similarities in the disease spread between SPMMV and CBSIs are not unexpected.
Expert guide to sweetpotato virology research for preparations against the epidemic
“If we can generate advance basic scientific information concerning how the SPMMV infects sweetpotato plants, how it is transmitted by vectors between plants, and circumstances fostering field spread of the virus, we will be better prepared to handle an epidemic that may arise from the virus,” Prof. Tugume states.
He adds: “we should be able to undertake these studies quickly because SPMMV is naturally incident on sweetpotatoes in Uganda, Kenya and Tanzania in levels causing less damage on its own at the moment, although this damage escalates when the virus occurs in multiple infections.”
The co-authors highlight serious research gaps for critical research investment in sweetpotato virology. Vector transmission is such an important aspect of virus disease epidemics of plants. Therefore, this study has proposed three possible explanations to account for the virus-vector and virus-host relationships of SPMMV. These are called hypothesis #1, #2, and #3, built in a fashion that allows experimentation to prove them right or wrong:
- Hypothesis #1: “SPMMV is opportunistically aphid-transmitted with potyvirus SPFMV as a helper virus.” This hypothesis postulates that SPMMV is transmitted by “chance” by a group of insects called aphids but this happens when SPMMV co-infects sweetpotatoes with another virus, SPFMV that is transmitted efficiently by aphids.
- Hypothesis #2: “Vector-mediated transmission of SPMMV is modulated by synergism with SPCSV.” Under this hypothesis, the concentrations of SPMMV in plant tissues increases when it co-infects with another virus, SPCSV, and this increases chances of SPMMV being picked by insects for transmission to other plants.
- Hypothesis #3: “SPMMV tropism and histo-localization changes upon co-infection with SPCSV.” How much viral concentration is found in different plant tissues can change depending on which tissues that are preferred by the virus. Certain plant viruses prefer to stay and multiply from certain tissues than others.
Dr. Alicai said, “If we can determine vector transmission dynamics including the actual vector(s) transmitting SPMMV, which plant tissues the virus prefers for its multiplication, and generate many complete sequences of SPMMV genomes, we will be better prepared for epidemics arising from the emergence of SPMMV”.
Sweetpotato is a vegetatively propagated plant in which the top-most 15-40cm part of the plant is used for initiating the new crop, a practice that is the main route of accelerated of virus spread in the cropping system. Also, insects especially aphids and whiteflies are the major vectors transmitting viruses in sweetpotato. The research gaps highlighted with respect to SPMMV require urgent attention for advance preparation in case an epidemic breaks loose on the sweetpotato cropping system.
This study has been published by the American Phytopathological Society (APS) in an open access journal, “Phytobiomes Journal”, and is freely accessible on https://apsjournals.apsnet.org/doi/10.1094/PBIOMES-05-22-0031-RVW
For more details, please contact;
Prof. Arthur Tugume
Lead Scientist
Department of Plant Sciences, Microbiology and Biotechnology
College of Natural Sciences (CoNAS)
Makerere University
Email: arthur.tugume@mak.ac.ug
Tel: +256772514841
Dr. Deusdedith Mbanzibwa
Tanzania Agricultural Research Institute (TARI),
Biosciences Centre, Dodoma, Tanzania
Email: d.mbanzibwa@yahoo.co.uk
Email: Tel: +255755881758
Dr. Titus Alicai
Root Crops Research Program
National Crops Resources Research Institute (NaCRRI)
National Agricultural Research Organization (NARO)
Email: talicai@hotmail.com
Tel: +256772970585
Hasifa Kabejja
Principal Communication Officer
College of Natural Sciences
Makerere University
Email: pr.cns@mak.ac.ug
Tel: +256774904211
Natural Sciences
Mak Researchers develop Innovative Integrated Wetlands-bivalve system to Mitigate Effects of Pollution in Aquaculture farms in the Lake Victoria Basin
By Hasifa Kabejja & Dr. Robinson Odong
Overview
The fisheries sub-sector in Uganda is crucial, supporting over 5 million livelihoods and providing essential protein for up to 17 million people, with an average consumption of 10 kg per capita. Uganda’s population is projected to double in the next 27 years, prompting the National Development Plan III to aim for a significant increase in fish production, with aquaculture expected to contribute 1 million MT by 2030. The Fisheries and Aquaculture Act 2022 emphasizes adherence to National Environmental Management principles to achieve sustainable production systems.
However, as aquaculture grows, the sector faces environmental challenges due to increased intensive production and on-farm waste, including nutrients from feed, uneaten feed, poor quality feeds, pseudofeces, escaped farmed fish, and residual chemicals. These pollutants pose risks such as habitat quality deterioration, biodiversity loss, eutrophication of waterways, and the emergence of drug-resistant pathogens.
Mitigating the effects of environmental pollution from aquaculture
Through a Project titled: Mitigating the Effects of Environmental Pollution from aquaculture on freshwater resources in Lake Victoria Basin (MEEP), researchers from Makerere University in collaboration with the National Environment Management Authority (NEMA) set out to assess the effects of aquaculture facilities and practices on Lake Victoria, its catchment rivers and wetlands. The team led by Dr Ronald Semyalo from the Department of Zoology, Entomology and Fisheries Sciences (ZEFS) at Makerere University subsequently examined the effectiveness of innovative technologies, such as integrated wetland-bivalve systems, in mitigating these impacts. They also reviewed the application of national environment and aquaculture regulations in controlling environmental pollution. The study surveyed fish farms in three districts of Buikwe, Jinja, and Mukono within the Victoria Water Management Zone. Other project team members were: Dr Jerome Lugumira from NEMA, Dr Robinson Odong and Mr. Drake Ssempijja from ZEFS, Makerere University, and Ms. Ritah Namisango, Senior Public Relations Officer at Makerere. The Project was supported by the Government of Uganda through the Makerere University Research and Innovations Fund (MakRIF).
During their engagement with different stakeholders in the fishing industry including the fish farmers from Jinja, Buikwe and Mukono, as well as experts from the Directorate of Water Resources at the Ministry of Water and Environment, NEMA, and the Directorate of Aquaculture Development at MAAF, the research team established that only 138 out of 380 registered fish farms were active, with 45.6% of the farms in Jinja, 35.5% in Mukono; and 18.8% in Buikwe. Overall, over 60% of the farms were inactive posing serious environmental threats.
Dissemination of the research findings
On 26th June 2024, the project team held a workshop at Colline Hotel Mukono to disseminate the research finding to stakeholders who included fish farmers from Buikwe, Jinja and Mukono, District Fisheries Officers, as well as representatives from NEMA and MAAIF. In the presentations, the team highlighted the environmental impacts of aquaculture practices and the possibility of innovatively using nature-based, environmentally friendly innovations as a mitigation measure. The presentations covered farm characteristics, water and feed management practices, water quality assessments and waste management methods. The participants engaged in discussion on the implications of the results and shared their experiences and challenges in managing aquaculture operations.
Key findings as disseminated by the PI
Out of the 380 farms, 119 were assessed. Below are the key findings;
- Environmental Impact Assessment: It was established that 81% of the farmers had not conducted Environmental Impact Assessments (EIAs) and Environmental audits. This, the researchers noted was one of the major causes of abandoned farms.
- Farm Characteristics: The majority of farms used earthen ponds (66.9%) and were semi-intensive (63.6%), relying on manufactured feed and pond fertilization. Intensive farms (30.5%) exclusively used manufactured feeds, while extensive farms (4.2%) relied solely on pond fertilization.
- Fish Species: Nile tilapia was the top choice (96.1%) for monoculture farms, while tilapia and catfish were preferred for polyculture systems (46.9%). Intensive farms predominantly farmed Nile tilapia.
- Demographics: Most respondents were male (90.7%), with a median age of 35 years. The largest age group was 31 to 59 years (43.2%).
- Fish diseases: The research revealed a number of diseases affecting aquaculture including: lesions/wounds on the belly and cysts on the scales, skin lesions and cysts on the belly, popping eyes and white substance on fins, open skin wounds, open wounds on the head, skin lesions – greyish, swollen eyes, whitish and black patches on the skin on the pelvic fin, wounds on the head.
- Water Use: Fish farms primarily relied on spring water and lake water. Other sources, such as streams, wells, and rivers, were also utilized. In most cases, the water source was shared with the community. Only a small percentage of respondents acknowledged any known disease outbreaks on their farms. There was a strong association between the district in which the farm was located and the water source used. Majority of those using lake water were in Jinja District, while most of those using spring water were in Mukono District. Additionally, there was a significant association between the fish species cultured and the water source used.
- Feed Management: A significant proportion of the farms heavily relied on factory-made feeds. These feeds were often used in combination with farm feed materials, such as maize bran, potato vines, yam leaves, and kitchen waste. A smaller number of farmers exclusively relied on farm-made feeds, while an even smaller percentage solely relied on pond fertilization. Manufactured feeds were used in various forms: powder and floating pellets, powder, crumble, and floating pellets, powder only, floating pellets only, and sinking pellets. The most prevalent method of feed delivery was feeding by response, while some farms also practiced feeding by ration.
- Waste Management: The findings indicated a concerning lack of treatment for aquaculture effluent, with majority of respondents (69%) releasing it directly into natural streams or wetlands. This highlights the need for improved environmental management practices. Common waste sources included faecal matter and dead fish. Most farms incinerated or buried solid waste.
- Water Quality: Measurements at the representative visited farms showed compliance with FAO optimal conditions for fish farms. The physicochemical parameters of the farms visited were in line with FAO optimal conditions for fish farms.
- Prevailing Regulatory System: A comprehensive gap analysis was conducted to supplement the findings from the survey. It aimed to identify weaknesses and areas for improvement in current policies and regulations governing aquaculture. It also evaluated the effectiveness of existing measures in addressing environmental pollution, waste management, and sustainable water use. This exercise provided a foundation for developing more robust and effective regulatory frameworks that support sustainable aquaculture practices, protect water resources, and enhance the overall environmental health of the Lake Victoria basin.
Project output
***Innovative Integrated wetlands-bivalves system was developed to mitigate the impact of pollution emanating from aquaculture on the environment
Effluent from poor aquaculture practices may contain uneaten feed residues and associated components, such as suspended solids, nutrient nitrogen and phosphorus and organic materials. If discharged without any form of treatment, such effluent contributes to excessive nutrient enrichment of water bodies, a phenomenon referred to as eutrophication. Eutrophic waters have diminished ecological value, for example are low in oxygen level and can lead to fish kills. Wetland plants, such as duckweeds can aid in cleansing of aquaculture effluent of excess pollutants, through various mechanisms. For example, the plant roots adsorb suspended solids, besides offering conducive attachment surfaces for beneficial microorganisms which perform various nutrient recycling roles. The plants also uptake excess nutrients, hence reducing their levels in water. Bivalves (Molluscs) are filter feeders, hence uptake and cleanse water of detrital or solid materials, hence augmenting the roles of the plants. The integration of wetlands-bivalves system offer synergistic roles in aquaculture effluent treatment. The plants and bivalves used in the treatment can in turn be removed and used for other beneficial purposes.
Presentation on policy gaps
During the dissemination workshop, Dr Jerome Lugumira, the Natural Resources Manager, Soils and Land Use at NEMA sensitized participants on the National Environment Act, 2019 with special emphasis on policy regulations for the aquaculture sector. He emphasized the need to acquire an EIA certificate before engaging in aquaculture. Highlighting the gaps in policy, Dr Lugumira noted that Schedule 4 of the National Environment Act, 2019 does not sufficiently guide the Fisheries sector; while the Physical Planning Act, 2010 is biased towards physical development planning, and the Water Act, 1997 provides for a waste discharge permit but no consideration of the extent of wastes discharged from fish farms of varying size and intensity is provided.
He further noted that the National Environment (Wetlands, Riverbanks and Lakeshores Management) Regulations, 2000 do not guide on areas where aquaculture best fits, indicating that the application of the 25% wetland area beyond which one needs approval is vague.
Additionally, he explained that the National Environment (Waste Management) Regulations, 2020 refer to fish waste generally and not whether it means waste from fish or all waste from fish farms, such as off-cuts, unwanted materials, and that the National Environment (Standards for Discharge of Effluent into Water or Land) Regulations, 2020 consider effluent discharge and not that released in-situ and that disposed directly into water via cages and into soil via land-based systems.
Dr Lugumira called for the review of the National Environment (Wetlands, Riverbanks and Lakeshores Management) Regulations, 2000, by requiring the mandated Lead Agency (WMD) to issue approvals for access to wetlands, and appending guidance on wetlands and lake areas where aquaculture is suitable. He suggested that submissions seeking approval from NEMA should have all required approvals from MAAIF, WMD and DLGs. “The assessment process should be supported by a technical officer skilled in fisheries sciences and not generalists,” he noted.
Overview on the state of capture fisheries and aquaculture in Uganda
Sharing an overview on the state of capture fisheries and aquaculture in Uganda, Mr. Geoffrey Dheyongera, Principal Fisheries Officer at MAAIF, noted that the global decline/stagnation in capture fisheries stocks had increased demand for fish, calling for a boost in fish production through stock enhancement in water bodies and promotion of aquaculture. “There is need for huge investment in aquaculture. The Aquaculture Policy targets 1 million MT from aquaculture through establishment of aquaparks with intensive management activities.”
Key concerns raised by the farmers
During the focused group discussions, participants highlighted a number of factors undermining the growth of the aquaculture sector. These include;
- Ignorance about the laws/policy guidelines
- Low skills and lack of exposure in aquaculture management
- Low numbers of technical staff to guide the farmers
- Inexperienced technical staff
- Cheating by fish seed producers
- Expensive and poor quality feeds
- Fluctuating prices of fish
- Competition with capture fisheries/negative attitude towards farmed fish
- Increased degradation of the environment which affects water quality
- High interest rates on loans
- Farmers fear for exorbitant taxes
Proposals for improvement
- Government should recruit technical staff to assist farmers
- Thorough training of extension staff
- Encourage value addition to farmed fish
- Integrate climate smart interventions in aquaculture
- Policies regulating the sector should be popularized
- Undertake periodical review of the existing policies
- Encourage multi-stakeholder involvement in the implementation of policies
- Invest in research responsive to fish and aquaculture sector needs
- Monitor quality of fish feeds to satisfy farmers’ needs and environmental safety
- Private hatchery operators must be supported by the responsible sector agencies to ensure quality seed. Likewise, fish seed must come from certified hatcheries.
- Inspection of farms should be strengthened
- Train farmers on proper aquaculture management practices
- Farmers should work in groups to reduce production costs, negotiate better prices for their products, access credit facilities and maximize profits
Remarks by the Guest of Honour, Mukono District CAO, and the Principal, CoNAS
In his remarks, the Guest of Honour, also Assistant Commissioner Aquaculture Management at MAAIF, Mr. Alio Andrew, guided the farmers on proper aquaculture practices, and encouraged Ugandans to invest in the fish sector. “The demand for fish has increased. Aquaculture remains a viable option,” he noted. He also raised the need to support private hatchery operators to produce quality seed, emphasizing that fish seed should only be bought from certified hatcheries. He highlighted the significance of biosecurity in aquaculture, and the need to collect appropriate data on the sector.
The CAO Mukono District called for intensified training of farmers in aquaculture management practices. She advised the farmers to work in groups if they are to make reasonable profits.
The Principal, College of Natural Sciences (CoNAS), Makerere University, Prof. Winston Tumps Ireeta, acknowledged the involvement of the community in research, and appreciated the fish farmers for actively participating in the project activities. He expressed gratitude to the Government of Uganda for the continued support towards research at Makerere University. Besides other initiatives geared towards improving research at Makerere, the Government is supporting over 700 research projects at Makerere through the Research and Innovations Fund. He also appreciated MAAIF and NEMA for the technical guidance extended towards the project.
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