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Introduction: Banana bunchy top disease (BBTD) caused by banana bunchy top virus (BBTV) poses a significant threat to Uganda's food and income security. Methods: To map BBTD spread and inform its management, a delimiting survey was undertaken covering the high-risk zones bordering the Democratic Republic of Congo (DR Congo) in the west, Rwanda and Tanzania in the south, and South Sudan in the north. BBTD is endemic in the DR Congo and present in Tanzania and Rwanda. The survey and environmental data were then used to map the vulnerability of Uganda's banana landscapes. Results and discussion: BBTD was only confirmed on 9% of sampled farms in north- and midwestern Uganda, with yield losses of 75% to 100%. Farmers observed BBTD over a 0.5-4.4-year period, suggesting a delayed detection. Suckers were the predominate planting materials used, increasing the risk of disease spread. Landscape suitability for BBTD was influenced by precipitation of the driest month, banana presence in 2016, land surface temperature difference (LSTD), the interaction between wind speed and LSTD, isothermality, wind speed, and the normalized difference vegetation index. These variables affect either or both the virus and aphid vector populations. Altitude did not influence the model, possibly due to disease introduction at mid to high altitudes through infected planting materials. The low-lying zones (around River Nile and Lakes Albert, Edward, and Victoria) are highly vulnerable. BBTD risk was low in northeastern Uganda with low banana production. The prediction map shows some suitable landscapes in the southwest that can expose this major banana production zone to BBTD, necessitating proactive measures. [ABSTRACT FROM AUTHOR]

Three hundred and ninety-four sweet potato accessions from Latin America and East Africa were screened by polymerase chain reaction ( PCR) for the presence of begomoviruses, and 46 were found to be positive. All were symptomless in sweet potato and generated leaf curling and/or chlorosis in Ipomoea setosa. The five most divergent isolates, based on complete genome sequences, were used to study interactions with Sweet potato chlorotic stunt virus ( SPCSV), known to cause synergistic diseases with other viruses. Co-infections led to increased titres of begomoviruses and decreased titres of SPCSV in all cases, although the extent of the changes varied notably between begomovirus isolates. Symptoms of leaf curling only developed temporarily in combination with isolate St V1 and coincided with the presence of the highest begomovirus concentrations in the plant. Small interfering RNA ( siRNA) sequence analysis revealed that co-infection of SPCSV with isolate St V1 led to relatively increased siRNA targeting of the central part of the SPCSV genome and a reduction in targeting of the genomic ends, but no changes to the targeting of St V1 relative to single infection of either virus. These changes were not observed in the interaction between SPCSV and the RNA virus Sweet potato feathery mottle virus (genus Potyvirus), implying specific effects of begomoviruses on RNA silencing of SPCSV in dually infected plants. Infection in RNase3-expressing transgenic plants showed that this protein was sufficient to mediate this synergistic interaction with DNA viruses, similar to RNA viruses, but exposed distinct effects on RNA silencing when RNase3 was expressed from its native virus, or constitutively from a transgene, despite a similar pathogenic outcome. [ABSTRACT FROM AUTHOR]