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The banana Xanthomonas wilt (BXW) disease, caused by the bacteriumXanthomonas campestris pv. musacearum (XCM), endangers the livelihoods ofmillions of farmers in the Great Lakes region of East and Central Africa. Thedisease was first identified in Uganda in 2001 and has since then also been reportedin Eastern Democratic Republic of Congo, Rwanda, Kenya and Tanzania. Thepathogen kills plants quickly and spreads rapidly over a large area making thedisease one of the most dreaded in banana (Musa spp.). The development of diseaseresistant banana cultivars remains a high priority, since farmers are reluctant toemploy labor-intensive disease control measures. Prospects of developing cultivarswith resistance to BXW through conventional breeding are limited, as no source ofgermplasm exhibiting resistance against XCM has been identified. Transgenictechnologies for banana may provide a timely and cost-effective alternative solutionto the BXW pandemic. The ferredoxin-like amphipathic protein (pflp) andhypersensitive response assisting protein (hrap), isolated from sweet pepper(Capsicum annuum) are novel proteins that can intensify the harpinPSS-mediatedhypersensitive response. The International Institute of Tropical Agriculture (IITA)has negotiated royalty-free license from Academia Sinica, Taiwan, patent holder,through the African Agricultural Technology Foundation (AATF) for access to thetechnology for bacterial wilt resistance. The partners, IITA, the NationalAgriculture Research Organization (NARO) in Uganda and AATF, have signed atripartite agreement for development of BXW-resistant transgenic bananas.Hundreds of transgenic lines of banana cultivars have been generated, which arescreened for disease resistance under laboratory conditions. Most promising lineswill be evaluated for efficacy against XCM in fields. ; Gatsby Charitable Foundation ; Peer Review

Objective: Since 2001 Xanthomonas wilt (BXW) has drastically reduced banana productivity in over 8000 km2 of farmland in Nord Kivu Province of eastern Democratic Republic of Congo. Banana constitutes the major source of income and staple diet for 700,000 residents of the affected area and an additional approximately five million people who depend on banana in the neighboring regions. This paper looks at some of the factors that have contributed to disease spread and presents strategies that could contribute to effective management. Methodology and results: The paper is based on a review of existing published literature, technical reports and some outcomes of disease surveys carried out in the eastern DRC. The dominant banana cultivar grown is Pisang Awak which is highly susceptible to BXW. The affected region is in the high altitude agroecological zone and disease appears to be transmitted through a combination of mechanisms including insect vectors and natural factors, e.g. water splash. Mechanical tools have less importance in disease spread, largely due to low effort made by farmers to management of banana plantations. In threatened areas, disease management has focused on training farmers to recognize disease and effective preventive measures. In affected areas efforts have been mostly directed to reducing inoculum and halting disease spread by destroying infected mats. Conclusion and applications of findings: Poor and inconsistent implementation of management measures, either due to lack of knowledge, persisting civil instability or lack of resources among other factors continue to limit success in managing the disease. Recent surveys show that the disease is spreading westwards, with increased risk of further spread through the Congo basin to key Musa producing regions in central and west Africa. Some of the factors that could slow down the westward spread of BXW include sparse human populations in the forest zone, unfavorably hot ecological conditions in the forest, and higher plantain densities in western DRC. ; Peer Review

Banana production in Eastern Africa is threatened by the presence of a new devastating bacterial disease caused by Xanthomonas vasicola pv. musacearum (formerly Xanthomonas campestris pv. musacearum). The disease has been identified in Uganda, Eastern Democratic Republic of Congo, Rwanda and Tanzania. Disease symptoms include wilting and yellowing of leaves, excretion of a yellowish bacterial ooze, premature ripening of the bunch, rotting of fruit and internal yellow discoloration of the vascular bundles. Plants are infected either by insects through the inflorescence or by soil-borne bacterial inoculum through the lower parts of the plant. Short- and long-distance transmission of the disease mainly occurs via contaminated tools and insects, though other organisms such as birds may also be involved. Although no banana cultivar with resistance to the disease has been identified as yet, it appears that certain cultivars have mechanisms to 'escape' the disease. Management and control of the disease involve methods that reduce the inoculum's density and spread of the pathogen. Removal of the male bud (de-budding) has proven to be very effective in preventing the disease incidence since the male bud appears to be the primary infection site. The economic impact of banana Xanthomonas wilt is not fully understood but its impact on food security in the region is very significant. While germplasm screening for the disease is ongoing, efforts to genetically engineer resistance in some banana cultivars are also making good progress. This paper presents a review of the disease and management strategies that have been successful in curtailing its spread. ; Peer Review

Banana Xanthomonas Wilt (BXW) poses a serious threat to livelihoods and food security for millions of households in Africa. Despite considerable investments in Uganda by the Government and other national and international stakeholders, the disease persists in the country after periods of significant resurgence. Building on the Agricultural Innovation Systems framework, this paper reviews the role of the major stakeholders involved in controlling the disease in Uganda. Next, using household survey data, it analyzes economic costs and benefits of adopting an integrated BXW control package for the Ugandan smallholder farmers. After 2015, there has been a significant reduction in both public and private investments in BXW management, which may contribute to future disease resurgence. Our analysis reveals a high level of partial adoption of BXW recommended practices, and just a third of farmers adopting a full control package. This means significant economic losses for non- adopters, as indicated by our findings that households adopting the full package registered a net balance of US$65 per acre higher than non-adopters. We find that disproportionally large costs need to be borne at the beginning of the process, while the benefits are distributed over time, which may present a barrier to adoption by resource-poor smallholders. ; Peer Review

Despite massive efforts by regional governments and partners in the East and Central African region towards fighting Xanthomonas Wilt of banana, the disease is reported to continue to spread to new areas and resurge in others it had been contained. The use of asymptomatic but infectious plants is hypothesized to play a leading role in the persistence of the disease and it's introduction to new areas. A model for the transmission of BXW by symptomless plants is proposed and analyzed. It incorporates both horizontal and vertical transmission modes and a dual source of inoculum in the force of infection. The basic reproduction number, R0, is obtained and it is found to completely determine the global dynamics of the model. By construction of a suitable Lyapunov function for the second additive compound system, the global stability of the endemic equilibrium is established. Numerical simulation and sensitivity analysis of the basic reproduction number indicate that the disease is mainly driven by parameters involving asymptomatic plants rather than symptomatic ones. ; Peer Review

Article purchased; Published online: 28 Feb 2010 ; Xanthomonas campestris pv. musacearum (Xcm) causes a disease onbanana (Musa spp.) and enset (Ensete spp.) known as banana xanthomonaswilt (BXW). Recent studies have shown that Xcm is a strain of X. vasicola(Aritua et al., 2008). However, the status of pathovars within thespecies remains unclear. Prior to its discovery in Uganda in October 2001,the disease had been limited to Ethiopia (first reported 1968). Since thenthe disease has spread to the Democratic Republic of Congo and Rwanda(observed in May 2004 and September 2005 respectively). BXW cancause high yield losses and is a high priority concern within the GreatLakes region. A comprehensive review of the pathogen and diseasewas recently published by Smith et al. (2008). Thus far, outbreaks inTanzania, Kenya and Burundi have only been referred to in symposiumproceedings and on various websites. These new records are thus officiallyreported here for the first time.In Tanzania, the disease was first reported in the Kagera region of northwest Tanzania, bordering Lake Victoria, Uganda, Rwanda and Burundi,in September 2005 (Mgenzi et al., 2006). Spread has continued, but not toother major banana growing areas. In Kenya, the disease was firstreported in September 2006 in the Teso District, of western Kenya,bordering Uganda (Anon, 2006). Spread has since been reported as slow.In Burundi the disease was first observed during October 2006 (Anon.,2006). The current status of BXW in Burundi is unclear with no recentsubstantiated reports.Bacterial cultures were isolated from diseased racemes from Tanzaniaand Burundi at CABI, UK and from Kenya at KARI (NARL). All cultureswere identified to species level at FERA by fatty acid profiling (MIDI system)and DNA analysis using X. vasicola specific primers (Aritua et al.,unpublished data) and partial sequencing of the gyrase B gene (Parkinsonet al., 2007). Koch's postulates were fulfilled for all strains at FERA bystem inoculation of banana plants (height approximately 30 cm) with abacterial suspension (200 lL with ~107 cfu ⁄ mL) under controlled environmentalconditions (minimum temperature 27ºC). Identification ofXcm isolates from Burundi and Kenya was further supported by OhioState University and KARI, respectively, using X. vasicola specific primers(Lewis-Levy Miller, unpublished data) that have a different target site tothose of Aritua et al. (unpublished data).Reference cultures are held by the UK National Collection of PlantPathogenic Bacteria, Accession Nos. NCPPB 4392-5 (Tanzania), 4434(Kenya) and 4433 (Burundi). ; Peer Review

For decades, Xanthomonas vasicola pv. musacearum (Xvm) has been an economically important bacterial pathogen on enset in Ethiopia. Since 2001, Xvm has also been responsible for significant losses to banana crops in several East and Central African countries, with devastating consequences for smallholder farmers. Understanding the genetic diversity within Xvm populations is essential for the smart design of transnationally reasoned, durable, and effective management practices. Previous studies have revealed limited genetic diversity in Xvm, with East African isolates from banana each falling into one of two closely related clades previously designated as sublineages SL 1 and SL 2, the former of which had also been detected on banana and enset in Ethiopia. Given the presumed origin of Xvm in Ethiopia, we hypothesized that both clades might be found in that country, along with additional genotypes not seen in Central and East African bananas. Genotyping of 97 isolates and whole-genome sequencing of 15 isolates revealed not only the presence of SL 2 in Ethiopia, but additional diversity beyond SL 1 and SL 2 in four new clades. Moreover, SL 2 was detected in the Democratic Republic of Congo, where previously SL 1 was the only clade reported. These results demonstrate a greater range of genetic diversity among Xvm isolates than previously reported, especially in Ethiopia, and further support the hypothesis that the East/Central Africa xanthomonas wilt epidemic has been caused by a restricted set of genotypes drawn from a highly diverse pathogen pool in Ethiopia.

For decades, Xanthomonas vasicola pv. musacearum (Xvm) has been an economically important bacterial pathogen on enset in Ethiopia. Since 2001, Xvm has also been responsible for significant losses to banana crops in several East and Central African countries, with devastating consequences for smallholder farmers. Understanding the genetic diversity within Xvm populations is essential for the smart design of transnationally reasoned, durable, and effective management practices. Previous studies have revealed limited genetic diversity in Xvm, with East African isolates from banana each falling into one of two closely related clades previously designated as sublineages SL 1 and SL 2, the former of which had also been detected on banana and enset in Ethiopia. Given the presumed origin of Xvm in Ethiopia, we hypothesized that both clades might be found in that country, along with additional genotypes not seen in Central and East African bananas. Genotyping of 97 isolates and whole-genome sequencing of 15 isolates revealed not only the presence of SL 2 in Ethiopia, but additional diversity beyond SL 1 and SL 2 in four new clades. Moreover, SL 2 was detected in the Democratic Republic of Congo, where previously SL 1 was the only clade reported. These results demonstrate a greater range of genetic diversity among Xvm isolates than previously reported, especially in Ethiopia, and further support the hypothesis that the East/Central Africa xanthomonas wilt epidemic has been caused by a restricted set of genotypes drawn from a highly diverse pathogen pool in Ethiopia. ; Wellcome Trust Multi-User Equipment Award; Wellcome Trust Institutional Strategic Support Fund; BBSRC Impact Accelerator Award grant and BBSRC LOLA award. ; https://onlinelibrary.wiley.com/journal/13653059 ; am2021 ; Forestry and Agricultural Biotechnology Institute (FABI) ; Microbiology and Plant Pathology

For decades, Xanthomonas vasicola pv. musacearum (Xvm) has been an economically important bacterial pathogen on enset in Ethiopia. Since 2001, Xvm has also been responsible for significant losses to banana crops in several East and Central African countries, with devastating consequences for smallholder farmers. Understanding the genetic diversity within Xvm populations is essential for the smart design of transnationally reasoned, durable, and effective management practices. Previous studies have revealed limited genetic diversity in Xvm, with East African isolates from banana each falling into one of two closely related clades previously designated as sublineages SL 1 and SL 2, the former of which had also been detected on banana and enset in Ethiopia. Given the presumed origin of Xvm in Ethiopia, we hypothesized that both clades might be found in that country, along with additional genotypes not seen in Central and East African bananas. Genotyping of 97 isolates and whole-genome sequencing of 15 isolates revealed not only the presence of SL 2 in Ethiopia, but additional diversity beyond SL 1 and SL 2 in four new clades. Moreover, SL 2 was detected in the Democratic Republic of Congo, where previously SL 1 was the only clade reported. These results demonstrate a greater range of genetic diversity among Xvm isolates than previously reported, especially in Ethiopia, and further support the hypothesis that the East/Central Africa xanthomonas wilt epidemic has been caused by a restricted set of genotypes drawn from a highly diverse pathogen pool in Ethiopia.

For decades, Xanthomonas vasicola pv. musacearum (Xvm) has been an economically important bacterial pathogen on enset in Ethiopia. Since 2001, Xvm has also been responsible for significant losses to banana crops in several East and Central African countries, with devastating consequences for smallholder farmers. Understanding the genetic diversity within Xvm populations is essential for the smart design of transnationally reasoned, durable, and effective management practices. Previous studies have revealed limited genetic diversity in Xvm, with East African isolates from banana each falling into one of two closely related clades previously designated as sublineages SL 1 and SL 2, the former of which had also been detected on banana and enset in Ethiopia. Given the presumed origin of Xvm in Ethiopia, we hypothesized that both clades might be found in that country, along with additional genotypes not seen in Central and East African bananas. Genotyping of 97 isolates and whole‐genome sequencing of 15 isolates revealed not only the presence of SL 2 in Ethiopia, but additional diversity beyond SL 1 and SL 2 in four new clades. Moreover, SL 2 was detected in the Democratic Republic of Congo, where previously SL 1 was the only clade reported. These results demonstrate a greater range of genetic diversity among Xvm isolates than previously reported, especially in Ethiopia, and further support the hypothesis that the East/Central Africa xanthomonas wilt epidemic has been caused by a restricted set of genotypes drawn from a highly diverse pathogen pool in Ethiopia.

Banana (Musa sp.) represents one of the most important world food crops after maize, rice, wheat and cassava. Many pests and diseases have significantly affected banana cultivation. Banana Xanthomonas wilt (BXW), caused by the bacterium Xanthomonas campestris pv. musacearum, is one of the most important diseases and currently considered as the biggest threat to banana production in the Great Lakes region of Africa including Uganda, Democratic Republic of Congo, Rwanda, Kenya, Tanzania and Burundi. The pathogen is highly contagious and its spread has endangered the livelihood of millions of farmers who rely on banana for food and income. The development of disease resistant bananas remains a high priority since farmers are reluctant to employ labor-intensive disease control measures and there is no host plant resistance among banana cultivars. The International Institute of Tropical Agriculture (IITA), in partnership with the National Agriculture Research Organization (NARO), Uganda and the African Agriculture Technology Foundation (AATF), have developed hundreds of transgenic bananas constitutively expressing the Hypersensitive Response Assisting Protein (Hrap) or Plant Ferredoxin Like Protein (Pflp) gene originated from sweet pepper (Capsicum annuum). These transgenic lines have exhibited strong resistance to BXW in the laboratory and screen house tests. The best 65 resistant lines were planted in a confined field trial in October 2010 at NARL, Kawanda, Uganda after approval from the National Biosafety Committee. This is a significant step toward development of transgenic banana cultivars resistant to BXW, which will boost the available arsenal to fight this epidemic disease and save livelihoods in Africa. These transgenic lines are under evaluation for disease resistance and agronomic performance in field conditions. This technology may also provide effective control to other bacterial diseases such as moko or blood disease of banana occurring in other parts of the world. ; Peer Review

Changes in land-use have been observed in banana-based systems in the African Great Lakes region affected by Xanthomonas wilt disease (XW) of banana. Through focus group discussions (FGDs) and the 4-cell method (to map the area under production and the number of households involved), changes in land-use were assessed in 13 XW-affected landscapes/villages along a 230 km transect from Masisi (where XW arrived in 2001) to Bukavu (XW arrived around 2014) in the Eastern Democratic Republic of Congo. Farmers' perceptions on the sustainability of new land uses were also documented. Soil nutrient content and erosion levels were measured for five major land-use options/trajectories on 147 fields across 55 farms in three landscapes along the transect. From banana being ranked the most important crop (92% of landscapes) before XW outbreaks, its importance had declined, with it grown on smaller farms by most households in 36% of the landscapes, while in 64% of cases by few households on smaller plots. Farmers uprooted entire banana mats or fields, expanding land under other crops. Species richness did not change at landscape level, although 21 crops were introduced at farm level. Banana is, however, still perceived as more sustainable due to its multi-functional roles. Soils under banana had better chemical attributes, while high erosion levels (Mg ha(-1) year(-1)) occurred under cassava (1.7-148.9) compared with banana (0.3-10.7) and trees (0.3-5.9). The shifts from banana could thus affect supply of key services and sustainability of the farming systems. This study offers a good basis for interventions in XW-affected landscapes.

Changes in land-use have been observed in banana-based systems in the African Great Lakes region affected by Xanthomonas wilt disease (XW) of banana. Through focus group discussions (FGDs) and the 4-cell method (to map the area under production and the number of households involved), changes in land-use were assessed in 13 XW-affected landscapes/villages along a 230 km transect from Masisi (where XW arrived in 2001) to Bukavu (XW arrived around 2014) in the Eastern Democratic Republic of Congo. Farmers' perceptions on the sustainability of new land uses were also documented. Soil nutrient content and erosion levels were measured for five major land-use options/trajectories on 147 fields across 55 farms in three landscapes along the transect. From banana being ranked the most important crop (92% of landscapes) before XW outbreaks, its importance had declined, with it grown on smaller farms by most households in 36% of the landscapes, while in 64% of cases by few households on smaller plots. Farmers uprooted entire banana mats or fields, expanding land under other crops. Species richness did not change at landscape level, although 21 crops were introduced at farm level. Banana is, however, still perceived as more sustainable due to its multi-functional roles. Soils under banana had better chemical attributes, while high erosion levels (Mg ha−1 year−1) occurred under cassava (1.7–148.9) compared with banana (0.3–10.7) and trees (0.3–5.9). The shifts from banana could thus affect supply of key services and sustainability of the farming systems. This study offers a good basis for interventions in XW-affected landscapes. ; Directorate-General for Development Cooperation and Humanitarian Aid, Belgium ; Peer Review

Changes in land-use have been observed in banana-based systems in the African Great Lakes region affected by Xanthomonas wilt disease (XW) of banana. Through focus group discussions (FGDs) and the 4-cell method (to map the area under production and the number of households involved), changes in land-use were assessed in 13 XW-affected landscapes/villages along a 230 km transect from Masisi (where XW arrived in 2001) to Bukavu (XW arrived around 2014) in the Eastern Democratic Republic of Congo. Farmers&rsquo ; perceptions on the sustainability of new land uses were also documented. Soil nutrient content and erosion levels were measured for five major land-use options/trajectories on 147 fields across 55 farms in three landscapes along the transect. From banana being ranked the most important crop (92% of landscapes) before XW outbreaks, its importance had declined, with it grown on smaller farms by most households in 36% of the landscapes, while in 64% of cases by few households on smaller plots. Farmers uprooted entire banana mats or fields, expanding land under other crops. Species richness did not change at landscape level, although 21 crops were introduced at farm level. Banana is, however, still perceived as more sustainable due to its multi-functional roles. Soils under banana had better chemical attributes, while high erosion levels (Mg ha&minus ; 1 year&minus ; 1) occurred under cassava (1.7&ndash ; 148.9) compared with banana (0.3&ndash ; 10.7) and trees (0.3&ndash ; 5.9). The shifts from banana could thus affect supply of key services and sustainability of the farming systems. This study offers a good basis for interventions in XW-affected landscapes.

The request for this training was initiated by L'Institut des Sciences Agronomiques du Burundi(ISABU), who invited IITA to provide tuition and materials for the production and use of semiselectivemedia for banana Xanthomonas wilt (*see box below). ISABU wanted to create the capacity toindependently diagnose and culture BXW from diseased banana plant samples.IITA were already working on BXW in Burundi under the Crop Crisis Control (C3P) projectmanaged by Catholic Relief Service (CRS). IITA and CRS liaised closely to develop a regionaltraining course, so that participants from Rwanda and DRC could also learn new techniques, whileencouraging greater coordination in the future. The original request for training was broadenedextensively to include new methods for surveillance and vigilance of all banana diseases.The course was attended by 11 participants from extension and research, Universities and IRAZ, aregional organisation. The trainers were Fen Beed and Komi Fiaboe (IITA), Eric Boa of the GlobalPlant Clinic (CABI) and Julian Smith (CSL), combining expertise in research, surveillance, vigilanceand diagnostics for plant diseases. All trainers are closely involved with BXW in East Africa.The training consisted of presentations, group discussions and practical demonstrations.Participants saw how to make the semi-selective medium for BXW and isolate bacteria. Theypracticed field and laboratory diagnostic techniques and carrying out participatory plant diseasesurveys, a new method tried here for the first time. They learnt how to use FTA cards to collectDNA samples from the field for laboratory analysis. FTA cards can be safely transported and sentoutside the country without the risk of spreading the disease. A prototype rapid serologicaldiagnostic test for BXW (lateral flow device or LFD) was demonstrated in the field and lab.Participants discussed how to quantify disease incidence and severity and learnt how to use GPSequipment and characterise field sites. The participatory disease surveys in Rugombo and Gitundahelped to pinpoint areas where more intensive assessments of BXW incidence and severity mightbe carried out. They also revealed how growers interpret symptoms and hence report potential newdiseases.The presentations described current knowledge of BXW and related advances in laboratorydiagnostics. The importance of publishing New Disease Reports was emphasised and the purposeof Pest Risk Analysis (PRA) explained in relation to BXW and other key diseases. Participantsreceived a comprehensive list of reference and lab materials which will assist in detection andcontrol of BXW and other banana diseases. Course feedback was positive and encouraging.Participants were asked to consider how they would use their new knowledge and methods afterthe course had ended and link more closely with national and regional partners.A proposal for further work is included in this report. A follow-on intensive programme oftraining, surveys and clinics seeks to reduce current threats to agricultural productivity through earlydetection of and timely advice on plant diseases. A practical blend of good science, effectivesurveillance and proven advisory services will strengthen the joint contributions of extension andresearch to increase food security, income generation and improved trade. The proposal highlightsfurther support required from national and regional organisations, as well as governments anddonors. These include local training for field and lab diagnostic techniques and expansion of theparticipatory disease surveys and strengthening of disease vigilance through the establishment of(mobile) plant health clinics. ; Catholic Relief Services ; United States Agency for International Development