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Open Access Article; Published online: 15 Nov 2018 ; Cassava brown streak disease (CBSD), caused by two viruses (Cassava brown streak virus and Ugandan cassava brown streak virus) is one of the most important diseases affecting cassava in East and Central Africa. The viruses are spread through infected stem cuttings and by the whitefly Bemisia tabaci. Recognized from coastal East Africa since the 1930s, it is only in recent years that outbreaks have occurred in higher altitude areas of the African Great Lakes region (Legg et al. 2011). CBSD caused by UCBSV was officially reported for the first time from eastern Democratic Republic of Congo (DRC) in Nord-Kivu Province by Mulimbi et al. (2012). Eastern DRC is on the 'front' of the westwards-spreading pandemic of CBSD, and it is vital to understand the identity and epidemiology of viruses associated with this outbreak. If CBSV was to be reported from DRC, this increased diversity of CBSD-causing viruses would increase the threat posed by the disease and make management more difficult.

Published Online:17 Aug 2021 ; Cassava plays a key role in ensuring food security and generating income for smallholder farmers throughout Central Africa, particularly in the Democratic Republic of Congo (DRC). This status is threatened, however, by cassava brown streak disease (CBSD), which has expanded its incidence and range in eastern DRC. The study described here comprises the first extensive assessment of temporal change in the occurrence of CBSD and its causal viruses in DRC, based on surveys conducted during 2016 and 2018. Cassava fields were inspected in Ituri, Nord-Kivu, Sud-Kivu, Tanganyika, and Haut-Katanga provinces within eastern DRC to record foliar incidence and severity of CBSD. Leaf samples were collected for virus detection and species-level identification. New occurrences of CBSD, confirmed by virus diagnostic tests, were recorded in two provinces (Haut-Katanga and Sud-Kivu) and nine previously unaffected territories, covering an area of >62,000 km2, and at up to 900 km from locations of previously published reports of CBSD in DRC. Overall, average CBSD incidence within fields was 13.2% in 2016 and 16.1% in 2018. In the new spread zone of Haut-Katanga, incidence increased from 1.7 to 15.9%. CBSD is now present in provinces covering 321,000 km2, which is approximately 14% of the total area of DRC. This represents a major expansion of the CBSD epidemic, which was only recorded from one province (Nord-Kivu) in 2012. Both Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus were detected in Ituri, Nord-Kivu, and Sud-Kivu, but only CBSV was detected in Haut-Katanga. Overall, these results confirm the increasing threat that CBSD poses to cassava production in DRC and describe an important expansion in the African pandemic of CBSD.