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
Makerere University Convocation has honored Mubiru Enock Joel with an award in recognition of his outstanding academic performance. Mubiru, who graduated with a Bachelor of Science in Mathematics and Physics, scored a CGPA of 4.91, making him the best student in the sciences at Makerere University this year. The award, which included a plaque and a cheque of UGX1 million, was presented to him by the Chair of the Convocation on January 14, 2025, the second day of the 75th graduation ceremony.
Overall, the College of Natural Sciences (CoNAS) presented 310 students for the award of degrees of Makerere University at the 75th graduation ceremony. Of these, 14 graduated with PhD (5 female 9 male), 36 MSc (10 female and 26 male) and 260 BSc (113 female and 147 male).
In the course of the 75th graduation ceremony that started on 13th January and will end on 17th January 2025, a total of 13,662 graduands will receive degrees and diplomas of Makerere University.
Of these, 143 will graduate with PhDs, 1,813 with Masters degrees, 11,454 with Bachelor’s degrees and 243 with postgraduate diplomas. 53 % of the graduands are female and 47% are male. 44% of the PhD graduands are female. A total of 491 graduands will receive first class degrees. 16% of the students will be graduating with post-graduate degrees and diplomas.
Chancellor’s Address
In his address, Makerere University Chancellor Dr. Chrispus Kiyonga congratulated the graduands on their success and expressed appreciation for the support provided by the lecturers, administrators, parents, and guardians. He emphasized that the success of the university is a collective effort, appreciating the faculty and University Council for their critical roles in delivering quality education.
Dr. Kiyonga also extended his gratitude to the President of Uganda, H.E. Yoweri Kaguta Tibuhaburwa Museveni, and the NRM government for their invaluable financial support to Makerere University. The Government has so far allocated UGX30 billion to Makerere University through the Research and Innovations Fund (Mak-RIF).
Looking to the future, Dr. Kiyonga encouraged the University to increase its outreach programmes, particularly in the agricultural sector. He proposed collaborations with medium- to large-scale farmers, where students could gain hands-on experience while also assisting farmers in local communities. He also advocated for stronger partnerships with the private sector to support the commercialization of innovations emerging from Makerere University.
Furthermore, the Chancellor highlighted the President’s directive to teach Political Economy to all university students. He stressed the importance of transforming Africa through the strategic utilization of its resources and emphasized the value of political economy knowledge in this process.
Vice Chancellor’s Address
In his remarks, Makerere University Vice Chancellor, Prof. Barnabas Nawangwe congratulated the graduands and expressed deep appreciation for the unwavering commitment of the teaching staff, administrators, parents, and guardians. He also welcomed the Chancellor, Dr. Chrispus Kiyonga, emphasizing that his vast experience would be an asset to the institution.
Prof. Nawangwe acknowledged the College of Natural Sciences for providing foundational training for all the other science-based disciplines at the University. He also commended the College for its ground-breaking research and contribution to the development of mathematics in the region. “The College of Natural Sciences is unique because it handles all the foundation disciplines for all the other science-based disciplines. But apart from the basic sciences, the College provides training and conducts research in critical applied science disciplines, including geology and petroleum studies, industrial chemistry, and others. The College is central in the development of mathematics in the East and Central Africa region and it has also taken the initiative to investigate the problem of poor performance in biology by secondary school students,” the Vice Chancellor noted.
He encouraged the graduands to seize every opportunity and to consider starting their own enterprises, using the knowledge and skills they have acquired during their studies. “Do not despair if you cannot find employment. Instead, reflect on the immense opportunities around you and consider entrepreneurship as a path to success,” he urged.
Message from the Minister of Education and Sports
On behalf of the First Lady and Minister of Education and Sports, Hon. Janet Kataaha Museveni, the Minister of State for Primary Education, Hon. Dr. Joyce Moriku Kaducu, congratulated the graduates and thanked the university for its commitment to excellence in education and research. She emphasized the transformative power of higher education and praised Makerere University for its contribution to the nation’s development.
She also expressed gratitude to the parents and guardians, acknowledging their critical role in the success of the students. “Your support has played an integral part in making this achievement possible,” she said.
Commencement lecture by Prof. Puleng LenkaBula
In her commencement lecture, Prof. Puleng LenkaBula, Vice Chancellor of the University of South Africa, expressed gratitude for the support that Makerere University and Uganda provided in the fight against apartheid. She encouraged the graduands to use the knowledge acquired to address the continent’s challenges, particularly in the transformation of Africa and the empowerment of women. Prof. LenkaBula called for greater collaboration among African intellectuals to create a better future for the continent, particularly through research that directly benefits communities.
Research Excellence and Teacher Recognition
At the ceremony, Makerere University recognized outstanding researchers and educators from CoNAS. The Senior Researcher Award was presented to Assoc. Prof. Juma Kasozi (Department of Mathematics), Assoc. Prof. Charles Masembe (Department of Zoology, Entomology and Fisheries Sciences), and Dr. Jamilu Ssenku (Department of Plant Sciences, Microbiology and Biotechnology). The Mid-Career Researcher Award went to Dr. Julius Mulindwa (Department of Biochemistry), Dr. Patience Tugume (Department of Plant Sciences, Microbiology and Biotechnology), and Dr. Patrick Ssebugere (Department of Chemistry), while Dr. Omara Timothy (Department of Chemistry), Dr. Mukiibi Ssewannyaga Ivan (Department of Geology and Petroleum Studies), and Dr. Sadik Mustafa Abubakar (Department of Plant Sciences, Microbiology and Biotechnology) were recognized as the best Early Career Researchers. In addition, Prof. Ann Akol (Department of Zoology, Entomology and Fisheries Sciences), Dr. Sadik Mustafa Abubakar, and Dr. Kalega Peggy (Department of Geology and Petroleum Studies) were honoured as the best teachers of the year from CoNAS.
Transcripts and Certificates
Graduates who participated in today’s ceremony can collect their transcripts from their respective colleges.
Natural Sciences
Meet Mubiru Enock Joel: Makerere University’s Top Performing Science Student of the Year
-
Natural Sciences2 weeks agoMeet Mubiru Enock Joel: Makerere University’s Top Performing Science Student of the Year
-
General2 weeks ago75th Graduation Highlights
-
Education2 weeks agoMakerere University Hosts Exchange Students from Norway for Field-Based Learning in Uganda
-
General1 week agoMak 75th Graduation Commences with 49 PhDs Conferred
-
Computing & IS1 week agoClose to 700 Graduate from CoCIS at the Mak 75th Graduation