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
Newly admitted students to the College of Natural Sciences (CoNAS) have been strongly encouraged to make academic excellence their top priority as they begin their university journey. During the official College orientation held on 6th August 2025, continuing students shared valuable insights aimed at helping the freshers adapt and thrive both academically and socially in the university environment.
Speaking at the event, Ms. Britah Kemigisha and Mr. Leakey Mbabazi, students of Conservation Biology and Petroleum Geosciences respectively, offered practical advice drawn from their experiences at CoNAS. The two students emphasized the importance of time management, consistent class attendance, and fostering healthy academic competition.
“Be ambitious and attend classes because attendance earns you some marks. Be competitive in a way that promotes excellence,” Mbabazi advised. He encouraged freshers to approach university life with purpose, noting that unlike in high school, university students must take personal responsibility for their learning outcomes. He recommended the use of professional networking platforms like LinkedIn, emphasizing their value in facilitating meaningful connections, expanding one’s professional network, discovering job opportunities, and staying updated on industry trends and insights.
Ms. Kemigisha underscored the importance of building supportive peer networks. “Form groups and inspire each other with rewards based on academic excellence,” she advised, emphasizing that academic group work, peer mentorship, and study circles can be powerful tools for motivation and accountability. According to her, surrounding oneself with goal-oriented individuals creates a positive learning environment that fosters growth and resilience, especially when faced with academic challenges.
The orientation programme served as a platform to introduce First Year students to the academic programmes, services, and student life at CoNAS and the University in general. The session led by the Deputy Principal, Prof. Juma Kasozi featured presentations by both College and University leaders, who sensitized the new students on key university policies, academic structures, and support services. School Deans and Heads of Departments in attendance briefed students on the specific programmes offered within their respective units. These included the Dean, School of Physical Sciences, Prof. Michael Owor; the Dean, School of Biosciences, Prof. Arthur Tugume; the Head, Department of Biochemistry and Systems Biology, represented by Dr Joel Isanga; the Head, Department of Chemistry, Dr Emmanuel Tebandeke; the Head, Department of Geology and Petroleum Studies, Dr Arthur Batte; the Head, Department of Mathematics, Dr Ismail Mirumbe; the Head, Department of Physics, Dr Denis Okello; the Head, Department of Zoology, Entomology, and Fisheries Sciences, Dr Godfrey Kawooya Kubiriza; the Head, Department of Plant Sciences, Microbiology, and Biotechnology represented by Dr Godwin Anywar, and a representative from the Department of Exercise and Sports Science. Students were also sensitized on the registration and examination processes, ICT support services, library services, fees payment policies, the Anti-sexual Harassment Policy, counselling and guidance services, the emerging leaders programme, and general welfare at the University.
On behalf of the Principal, the Deputy Principal, Prof. Juma Kasozi warmly welcomed the newly admitted students to the College.He provided an insightful overview of the key academic units and programmes offered both within the College and across the University. In his address, Prof. Kasozi congratulated the students on securing admission into one of the most competitive, vibrant, and intellectually rigorous colleges within the University. He encouraged the students to take full ownership of their academic journey, emphasizing the importance of commitment, discipline, and focus from the very beginning. Highlighting the value of hard work and determination, he reminded them that the foundation they lay now will shape their future success.
In his address, the Manager of the Counselling and Guidance Centre at the University, Mr. Henry Nsubuga, emphasized the importance of safeguarding mental health. He urged students to prioritize their psychological well-being, noting that maintaining a healthy mind is fundamental for academic success and overall personal development. Mr. Nsubuga encouraged students to actively seek support and adopt positive coping mechanisms to navigate the pressures of academic life.
The lectures are expected to commence on Monday, 11th August 2024.
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Natural Sciences
Makerere Researchers Call for Urgent Conservation of Medicinal Plants in Eastern Uganda
Researchers from the Department of Plant Sciences, Microbiology, and Biotechnology at the College of Natural Sciences (CoNAS), Makerere University have highlighted the urgent need to conserve medicinal plants in the face of increasing threats from climate change, over-harvesting, and habitat destruction.
Despite Namutumba District’s rich diversity of medicinal plants, conservation efforts are limited, and several species are already classified as globally and nationally threatened. This highlights the urgent need for focused conservation strategies to safeguard these vulnerable medicinal plants.
Under a project titled “Knowledge, Attitudes, and Conservation of Commonly Traded Medicinal Plants in a Climate-Changing Environment in Eastern Uganda,” a team of researchers led by Dr Patience Tugume documented 174 medicinal plant species. The goal was to assess the existential threats facing these plants due to unsustainable harvesting practices and the lack of effective conservation measures. These species are widely used to treat various health conditions, including malaria, syphilis, diabetes, hypertension, and certain cancers. The findings of the study are intended to guide the development of species-specific, evidence-based interventions to curb possible extinction and loss of medicinal plant resources. The research revealed troubling trends in the availability of key medicinal plants, including:
- The herbalists mostly collected their medicinal plants from bushlands (92.0%), markets (82.3%) and wetlands (74.7%) and were rarely cultivated. This is of great concern regarding the conservation and future availability of these resources.
- It was noted that 36% of the herbal products were made from roots, which presents a conservation threat since the heavy utilization of roots affects the regeneration of the medicinal plants.
- Common plants used were: Kigelia africana (Naibere), Erythrina abyssinica (Ekiyirikiti) and Geranium sauveolens (Lokowe). Kigelia africana was the most cited species by the herbalists, indicating heavy utilization and a high conservation threat if deliberate measures are not taken to ensure its future availability.
- Almost all respondents (289, 96.3%) acknowledged a considerable decline in the availability of 13 medicinal plants species including Aloe wollastonii (Ekigagi), Commiphora africana (Nkulidho), Myrica kandtiana (Mukikimbo) and Acacia sieberiana (Mufundawuzi).
- Four plant species i.e. Tamarindus indica (Enkoge), Warburgia ugandensis (Balwegira), Mitragyna rubrastipulata (Mutamatama) and Mondia whitei (Mulondo) appear on the Red List of Globally and Nationally Threatened Species and were mentioned among the plants whose population has greatly declined.
- The causes of decline in availability of medicinal plants included climate change, overharvesting, agricultural expansion, habitat destruction, land use change and inadequate regulations.
- There were no medicinal plant conservation efforts by herbalists.
The study recommended the following practices to ensure conservation of the medicinal plants:
- Promote the use of sustainable harvesting techniques to ensure conservation of medicinal plants.
- Conduct capacity building for stakeholders in the medicinal plants sector on conservation, value addition and standardization.
- Establish community botanical gardens raw plant collection and sensitization programmes.
- Advocate for agroforestry among herbalists to reduce the dependence on natural habitats.
- Develop and enforce regulations on accessing natural areas for medicinal plants.
- Promote conservation awareness campaigns.
Research Dissemination in Namutumba District
At the research dissemination workshop held in Namutumba District on 23rd July 2025, and attended by district leaders, researchers, and local herbalists, the project team led by Dr Patience Tugume expressed hope that the insights gained from the project, particularly in medicinal plants conservation approaches, will be invaluable for minimising the decline in medicinal plants.
In her remarks, Dr Tugume, thanked the Government of Uganda through the Makerere University Research and Innovations Fund (MakRIF) for funding the project. She expressed gratitude to the research team composed of Dr Abubakar Sadik Mustafa, Dr Jamilu E. Ssenku, Dr Savina Asiimwe, and Dr Abdul Walusansa who have worked with her closely from project inception in February 2024. She further thanked the research assistants and all respondents, mainly the herbalists that participated in the study.
In a special way, she appreciated Mr. Fred Aggrey Bangu (Resident District Commissioner), Mr. Ofwono Emmanuel (Chief Administrative Officer), Mr. Kiire Noah (Communication Officer), Mr. Mugunywa Enock (District Community Development Officer), Mr. Kirya Moses (District Environmental Officer), Mr. Bamusubire William (District Forest Officer) and the leaders of herbalist associations for providing support throughout the study and sparing time to attend the dissemination workshop.
Addressing the participants, the Resident District Commissioner, Mr. Fred Aggrey Bangu urged all stakeholders to engage in a collaborative discussion on how the study findings can be translated into practical solutions to promote sustainable use and conservation of commonly used medicinal plants in Namutumba District amidst adverse effects of climate change.
Mr. Ofwono Emmanuel, the Chief Administrative Officer, praised the Makerere research team for selecting Namutumba as the study area. He said the research served as an eye-opener to the district officials and community, especially regarding the pressure exerted on natural medicinal resources.
Report compiled by Dr Patience Tugume and Dr Abubakar Sadik Mustafa – Department of Plant Sciences, Microbiology and Biotechnology, CoNAS, Makerere University
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