Browsing by Author "Aloyce, Agatha"

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Biovar 2 of Ralstonia solanacearum Species Complex Causes Tomato Bacterial Wilt Disease in Tanzania
(Science Alert, 2020-03) Aloyce, Agatha; Ndakidemi, Patrick A.; Mbega, Ernest
Background and Objective: Bacterial wilt disease (BWD) caused by complex species of Ralstonia solanacearum (RSSC) has been categorized as one of the most significant plant diseases in the world. It is a serious problem of tomato and causes significant economic losses of tomato in Tanzania. The purpose of this study was to determine biovars of RSSC causing tomato BWD in Tanzania. Materials and Methods: Tomato stems showing typical symptoms of BWD were collected from main agro-ecological regions and were characterized by pathological and carbohydrate oxidation tests. The least significance difference (LSD) procedure was used for mean separation (p = 0.05) of disease incidence and severity. Results: A total of 29 out 40 RSSC isolates from infected tomato stems produced typical colonies of RSSC on triphenyl tetrazolium chloride medium out of which 19 (52%) were pathogenic on tomato variety Tanya. Carbohydrate oxidation test showed that most (90%) predominating isolates in main agro-ecological regions belong to biovar 3 while the rest (10%) belong to biovar 2 and prevail in the southern zone of Tanzania. This is the first report of prevalence of biovar 2 of Ralstonia in Tanzania and suggests a recent introduction of biovar 2 in tomato fields in Tanzania. Conclusion: Biovar 2 of RSSC is reported for the first time to cause tomato bacterial wilt disease in Tanzania. This alerts plant health regulators to embark on necessary phytosanitary measures to prevent further spread and/or introduction of the disease considering its quarantine status in different countries.
Characterization and management of bacterial wiltcausing pathogen(s) of tomato in Tanzania
(NM-AIST, 2020-04) Aloyce, Agatha
Bacterial wilt disease (BWD), caused by Ralstonia solanacearum (Smith) is one of the most destructive tomato diseases globally. A research was carried out from 2017 to 2019 to assess the incidence and severity of tomato BWD, characterize the pathogen and evaluate effects of selected pesticidal plants against BWD. Results indicated that 55.17% of the surveyed fields in different districts in Tanzania were significantly (p ≤ 0.05) infected by BWD with overall disease incidences and severities ranging from 5.8 to 44.6% and 10.70 to 59.30% respectively. Majority (70%) of farmers used synthetic chemicals, 13% used botanical, 10% did crop rotation and 7% did not use any BWD management measure. A total of 29 Ralstonia isolates were isolated from infected tomato plants out of which 19 (52%) were pathogenic on tomato variety Tanya. Carbohydrate oxidation test showed that most (90%) predominating isolates in the main agro-ecological zones belong to biovar 3 while the rest (10%) belong to biovar 2 and prevail in the southern zone of Tanzania. This is the first report of prevalence of biovar 2 of Ralstonia in Tanzania and it alerts global plant health regulators to prevent new introduction and/or spread of Ralstonia. Phylogenetic analysis based sequence data generated from the 16S-23S internal transcribed spacer (ITS) of isolates revealed that most (80%) were phylotype I and III and the rest (20%) were phylotype II of R. pseudosolanacearum and R. solanacearum geno-species respectively. Such results implied that BWD in the country is caused by diverse Ralstonia populations. In screening the effect of 20 plant extracts, the findings revealed that R. solanacearum can be managed using extracts from one of the tested plants (Patent Application ID Number G190916-2061) which was as effective as the positive control (ampiclox) in inhibiting growth of Ralstonia in in-vitro conditions. It produced inhibition zone of 19.25 mm almost similar to 20.58 mm by the ampiclox compared with 0.00 mm of the negative control. Similarly, the application of the extracts of the most effective plant managed BWD severity on tomato seedlings grown in screen-house 100% compared with the untreated seedlings which wilted. Therefore the extract from the most effective plant will be recommended after patenting for developing effective and sustainable management strategies of BWD in Tanzania based on the pathogen characteristics as generated during this study.
Climate change and its impact on wheat stem rust disease dynamics in Tanzania
(Springer Nature, 2024-03-29) Aloyce, Agatha
Wheat stem rust (Puccinia graminis f. sp. tritici) remains a major threat to global wheat production, yet its dynamics in Tanzania, especially in the context of climate change (CC), are not well understood. This research, conducted during the 2023 wheat growing season, investigates the impact of climate change on wheat stem rust in key wheat-growing regions of Tanzania of Manyara, Mbeya, Iringa, Kilimanjaro, and Arusha. The results show widespread occurrence of wheat stem rust across all surveyed fields, with the highest disease severity observed in the northern regions (Manyara, Arusha, and Kilimanjaro), where warmer temperatures (23–25 °C) and higher humidity (55–65%) create conducive conditions for disease development. Conversely, the southern regions, characterized by cooler temperatures (12–13 °C) and more variable humidity (55–75%), exhibited lower disease levels. The research also revealed that traditional wheat varieties, such as Mamba and Juhudi, are more susceptible to stem rust compared to modern varieties like Riziki and Njombe 7, with the Sifa variety showing significant resistance. Pearson correlation analysis confirmed strong positive correlations between disease severity and both relative humidity (r = 0.67, p < 0.01) and temperature (r = 0.72, p < 0.01). The findings suggest that rising temperatures and fluctuating rainfall patterns due to CC will likely intensify wheat stem rust incidence and severity in Tanzania, with projections indicating an increase of ≥20% in incidence and ≥30% in severity by mid-century. This research fills a critical gap in understanding the regional effects of CC on wheat diseases in sub-Saharan Africa. It underscores the need for adaptive management strategies, including the promotion of resistant wheat varieties, to mitigate future risks to wheat production. The research also highlights the importance of increased investment in research and policy to build agricultural resilience and enhance food security. Future research should focus on improving climate models for disease forecasting and exploring sustainable, region-specific management strategies for wheat stem rust. These findings offer valuable insights into the localized impacts of climate change on wheat diseases and provide actionable guidance for enhancing disease management strategies and promoting climate-smart agricultural practices in Tanzania.
Climate change and plant protection: challenges and innovations in disease forecasting systems in developing countries
(PAN, 2025-06-13) Aloyce, Agatha
Plant disease forecasting plays a crucial role in managing outbreaks and mitigating economic and health impacts, thereby contributing significantly to plant protection efforts. This proactive approach assesses the likelihood of disease outbreaks and increases in disease intensity, enabling timely intervention and resource optimization. However, climate change exacerbates this challenge by altering pathogen evolution and host-pathogen interactions, fostering the emergence of new pathogenic strains, shifting pathogen ranges, and expanding the geographic spread of plant diseases. In developing countries, these changes are compounded by limited resources and inadequate infrastructure, creating significant challenges for forecasting systems and plant protection efforts. The primary objective of this review was to assess the impact of climate change on plant disease forecasting systems, with a focus on biotic and abiotic stresses such as temperature changes, altered precipitation patterns, and extreme weather events. A systematic literature review was conducted using databases such as PubMed, Web of Science, and Google Scholar, selecting peer-reviewed studies published between 2020 and 2024. Key data on research objectives, methodologies, results, and implications were extracted and synthesized, demonstrating how climate induced stresses affect components of the disease tetrahedron, including host susceptibility, pathogen virulence, environmental conditions, and vector dynamics. The findings reveal that climate change significantly affects forecasting systems and plant protection strategies, emphasizing the need for reliable, and cost-effective forecasting models adaptable to diverse and evolving climate conditions, especially in resource-constrained settings. This review underscores the importance of developing innovative and context-specific strategies to enhance forecasting capabilities and plant protection. Future research should focus on advancing forecasting technologies, addressing data gaps, and adapting systems to evolving climate conditions to better safeguard food security and environmental sustainability.
Diversity of Ralstonia solanacearum Causing Tomato Bacterial Wilt Disease in Tanzania
(Knowledgia Scientific, 2023) Aloyce, Agatha; Mbega, Ernest
Background and Objective: Ralstonia solanacearum (Smith) is one of the most destructive bacterial plant pathogens in the world. It causes bacterial wilt disease (BWD) in several plant species including tomato. This research was carried out to understand the diversity of the causing bacterial isolates and develop management strategies based on the characteristics of the prevailing pathogens in Tanzania. Materials and Methods: Forty isolates were collected from the infected tomato plants preserved in the laboratory from the BWD field survey in 2018 in Tanzania. Isolates were grown on TTC medium and DNA was extracted from a single colony of each isolate using the bacterial DNA extraction kit for molecular analysis using PCR. The similarity coefficients were predicted by the Dice technique for all possible isolate pairs based on the fingerprint groups. Finally, the aligned sequences were contrasted with the standard strains in the National Center for Biotechnology Information (NCBI) database to determine resemblance using the Basic Local Alignment Tool (BLAST). Results: According to the results of the phylogenetic analysis, 80% of the samples belonged to phylotypes I and III of the R. pseudosolanacearum and 20% to phylotype II of the R. solanacearum genospecies, respectively. Findings have shown that Tanzania has a diversified population of the Ralstonia solanacearum species complex that causes tomato BWD. Two species and three phylotypes of infections that cause tomato BWD were found to predominate in various agro-ecological zones across the nation. Phylotypes I and III of Ralstonia pseudosolanacearum and phylotype II of Ralstonia solanacearum were the isolates that were found. Conclusion: Strong standard phytosanitary measures must be implemented worldwide by plant health authorities as a result of the first report of phylotype II of RSSC in Tanzania.Background and Objective: Ralstonia solanacearum (Smith) is one of the most destructive bacterial plant pathogens in the world. It causes bacterial wilt disease (BWD) in several plant species including tomato. This research was carried out to understand the diversity of the causing bacterial isolates and develop management strategies based on the characteristics of the prevailing pathogens in Tanzania. Materials and Methods: Forty isolates were collected from the infected tomato plants preserved in the laboratory from the BWD field survey in 2018 in Tanzania. Isolates were grown on TTC medium and DNA was extracted from a single colony of each isolate using the bacterial DNA extraction kit for molecular analysis using PCR. The similarity coefficients were predicted by the Dice technique for all possible isolate pairs based on the fingerprint groups. Finally, the aligned sequences were contrasted with the standard strains in the National Center for Biotechnology Information (NCBI) database to determine resemblance using the Basic Local Alignment Tool (BLAST). Results: According to the results of the phylogenetic analysis, 80% of the samples belonged to phylotypes I and III of the R. pseudosolanacearum and 20% to phylotype II of the R. solanacearum genospecies, respectively. Findings have shown that Tanzania has a diversified population of the Ralstonia solanacearum species complex that causes tomato BWD. Two species and three phylotypes of infections that cause tomato BWD were found to predominate in various agro-ecological zones across the nation. Phylotypes I and III of Ralstonia pseudosolanacearum and phylotype II of Ralstonia solanacearum were the isolates that were found. Conclusion: Strong standard phytosanitary measures must be implemented worldwide by plant health authorities as a result of the first report of phylotype II of RSSC in Tanzania.
Identification and Management Challenges Associated with Ralstonia solanacearum (Smith), Causal Agent of Bacterial Wilt Disease of Tomato in Sub-Saharan Africa.
(Science Alert, 2017) Aloyce, Agatha; Ndakidemi, Patrick; Mbega, Ernest
Tomato is the world's most consumed vegetable crop after potato and it is source of vitamins, minerals, fiber, lycopene, β-carotene and income. Despite its significant importance tomato can heavily be attacked by different pathogens including Ralstonia solanacearum that incites bacteria wilt disease. The disease is very devastating causing a considerable yield loss worldwide. The pathogen can survive in plant debris, infected plants and host weeds and spread from one field to another by irrigation or flood water, soil, farm equipment and workers and weeds which usually grow along waterways and it is difficult to manage due to complication in biology, nature of infestation and wide host range. In areas like the Sub-Saharan Africa where there exists a wide diversity of plant species, the pathogen becomes even more difficult to manage. It is on this basis that this review article, clearly discusses challenges for bacterial wilt disease identification and management in tomato farming systems with respect to the diagnosis methods used, pathogen genetic diversity and host range and pathogen survival mechanisms under different environment. The information will empower the responsible personnel involved in tomato production chain to have clear information about the pathogen and management options available against the disease in Sub-Saharan Africa.
Survey and conventional management methods of bacterial wilt disease in open fields and greenhouses in Tanzania
(Springer International Publishing, 2019-06-12) Aloyce, Agatha; Ndakidemi, Patrick; Mbega, Ernest
A study was conducted from January to February 2018 to determine bacterial wilt disease (BWD) incidence and severity in open-field and greenhouse environments in twelve tomato growing districts in Tanzania. About 220 farmers were interviewed to assess their knowledge on BWD by using a semi structured questionnaire. Results indicated significant (p < 0.05) difference of BWD incidence and severity among districts. Similarly, BWD incidence and severity were significantly (p < 0.05) higher in greenhouses than in the open field environments implying that BWD is a major challenge in tomato under greenhouse than in open-field environments. Most of the farmers were not certain about BWD symptomology and management. Majority (>80% of 220 respondents) of farmers could not identify sources of BWD in environment and do not adhere to sanitation measures recommended for greenhouse tomato production. 90% of the interviewed famers ventured into greenhouse tomato production by imitating from neighbors without technical guidance. To manage BWD, majority (70%) of farmers use chemicals which they reported as ineffective, 13% use botanical, 10% do crop rotation which was reported to be not practical because of land scarcity and long time that Ralstonia solanacearum can survive. Rest (7%) of farmers do not use any BWD management measure. There was no report of either use of disease resistant cultivars or biological control as a strategy for BWD management in the study area. There is therefore need to develop techniques for farmers to manage the BWD by exploring promising options such as use of effective botanical extracts.