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
Overview
The Ugandan government has increasingly recognized the critical role of science education in driving the nation’s economic development. As such, it has put in place deliberate policies aimed at popularizing science education in schools. This initiative seeks to equip the youth with the knowledge and skills necessary to contribute effectively to the country’s development. Since 2004, science education has been made compulsory in lower secondary schools, and the Uganda Government has continuously emphasized the importance of science and technology through policies like the National Science, Technology, and Innovation (STI) Policy, introduced in 2009. These policies aim to create a strong foundation for the country’s “Transformation for Prosperity,” focusing on technological innovation and development. The introduction of astronomy and space science as part of the curriculum supports this vision, offering students the tools to explore scientific concepts that will drive future innovation.
About the Project – Use of Astronomy and Space Science to Promote Science Education in Schools
In an initiative geared towards bolstering science education in Uganda, Makerere University Department of Physics is leveraging the wonders of astronomy and space science to ignite curiosity and enthusiasm among learners. The project, led by Prof. Florence Mutonyi D’ujanga from the Department of Physics has reached 10 schools in Kampala, Luwero, and Mukono districts, using the vast universe to inspire the next generation of scientists, engineers, and mathematicians. The astronomy outreach activities have impacted numerous schools across different regions in Uganda. The initiative started during the COVID-19 lockdown, with initial outreach to nearby schools in Kampala. As the programme gained momentum, it expanded to various districts, benefiting students from both primary and secondary levels. The schools that have participated in the programme include, Kampala: Makerere College School and Makerere CoU Primary School, Luwero: Mulusa Academy (Wobulenzi), Wobulenzi Bright Parents, Janan Luwum S.S., and Janan Luwum Nursery & P/S, MUkono: Our Lady of Africa S.S., Kyesereka CoU P/S, Mpoma Royal College, and Mpoma Junior School.
Aims and Objectives of the Project
Funded by the Government of Uganda through the Makerere University Research and Innovations Fund (MakRIF), the central aim of this initiative was to use astronomy and space science to capture the imagination of students, encouraging them to embrace the study of science and mathematics. “By engaging students in hands-on, interactive learning activities, the project seeks to improve their performance in these critical subjects. The initiative focuses on making science enjoyable, accessible, and inspiring, fostering a positive attitude toward the subject from an early age,” explained Prof. D’ujanga.
Activities conducted
The project began with a questionnaire to assess the students’ initial understanding of astronomy, followed by tailored outreach activities that addressed gaps in knowledge and sparked excitement about the subject. The activities included;
- Telescope Assembly: Students learned to assemble telescopes using local materials, helping them gain a hands-on understanding of how astronomy tools function.
- Sky Viewing: Students had the opportunity to observe celestial bodies like stars, planets, and constellations, experiencing the universe up close.
- Cultural Astronomy Storytelling: This component introduced students to the rich cultural narratives surrounding astronomy, linking science with history and tradition.
- Astronomy Quiz Sessions: Fun, educational quizzes challenged students’ knowledge of astronomy, stimulating a deeper interest in the subject.
- Planetarium Shows: The project also featured immersive planetarium shows, which are a highlight for many students. These shows provided an exciting visual experience, where learners could see projections of stars, planets, and other celestial phenomena. The planetarium is at the heart of this outreach programme. Traditionally used for educational purposes in the field of astronomy, the planetarium has a hemispheric domed ceiling, which serves as a projection screen for images of celestial objects. The immersive environment fosters curiosity and excitement among learners, laying a solid foundation for further study in science. One of the main objectives of the planetarium shows is to break down the myth that sciences are difficult. By using visual and interactive methods, the project demonstrates that learning about space and the universe can be both fun and inspiring.
Project research dissemination event
On 21st March 2025, the project team hosted a dissemination event at Makerere University to present and share their research findings. The event was presided over by Prof. Winston Tumps Ireeta, the Principal of the College of Natural Sciences (CoNAS) and Acting Deputy Vice Chancellor in charge of Finance and Administration at Makerere University. The event was attended by students, school administrators, as well as representatives from MakRIF and the Ministry of Science, Technology, and Innovation. In her address, the Project Principal Investigator (PI), Prof. Florence D’ujanga, emphasized the importance of sparking curiosity in students to encourage them to pursue scientific studies. “By making astronomy and space science more accessible and engaging, this project seeks to inspire greater interest in science education, ultimately benefiting Uganda’s long-term development in critical fields such as technology, engineering, and mathematics,” she explained.
On behalf of MakRIF, Dr. Mercy Rebekah Amiyo expressed appreciation to the research team for their invaluable initiative in promoting the study of science through astronomy. Dr. Amiyo praised the team’s dedication to making complex scientific concepts more engaging. She called upon the project team to secure property rights and take proactive steps toward the commercialization of the project.
In his remarks, the Guest of Honour, Prof. Winston Tumps Ireeta emphasized the importance of nurturing scientists who understand principles rather than simply memorizing frameworks. He emphasized the importance of early exposure for children to develop an appreciation for science. He expressed gratitude to the Government of Uganda for its continued support towards research activities at Makerere University.
Testimonies by students
Sharing their testimonies about the project, Jonathan Mugabi and James Tanzinge, both S.4 students at Makerere College School, expressed heartfelt gratitude for the opportunity it provided. They noted that the project had ignited a newfound passion for research, significantly expanding their interest in exploring scientific topics. Through their participation, they were introduced to essential scientific vocabulary, which has helped to deepen their understanding of complex concepts. Additionally, the project exposed them to cutting-edge technology, fostering a sense of excitement and curiosity about the role of innovation in science. As a result, both students have developed a strong desire to continue their studies in the sciences at a higher level, inspired by the hands-on experiences and knowledge they gained from this initiative.
Click on the link below for the pictorial of the dissemination conference;
https://drive.google.com/drive/folders/1Wv5xLOwiNe8Tc9uOWBpt9xvOtwffLHdo?usp=sharing
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