TITLE:
Multiple Cassava Viruses’ Co-Infections and Resurgence of Pests Are Leading to Severe Symptoms and Yield Losses on Cassava in the South-Kivu Region, Democratic Republic of Congo
AUTHORS:
E. B. Bisimwa, D. R. Birindwa, M. O. Yomeni, N. Rudahaba, K. Byamungu, C. Bragard
KEYWORDS:
Cassava Genotypes, Distribution, Climate Factors, South-Kivu, Re-Emergence, Whitefly
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.10 No.11,
November
15,
2019
ABSTRACT: A survey was completed during the last five years
(2014-2018) to update and assess changes in the cassava pests and diseases
occurrence as well as to understand how these changes occur regarding the
recent new viruses spread under a climate change context in the South-Kivu
region, Democratic Republic of Congo. The eight territories of South-Kivu were
surveyed during the rainy seasons from 2015 until 2017 except for Uvira and Fizi
where data were recorded in 2018 regarding the prevalence of unstable agro
ecological factors which may influence pest and diseases dynamic in these two
territories. During the data collection, pests and disease incidence and
severity were recorded as well as the sampling of cassava leaves for molecular
viruses’ detection. The recorded data showed that Cassava mosaic disease (CMD)
remains the most encountered disease (75% - 80%) and its vector (the whitefly Bemisia tabaci) the most important pest
(10 - 18 adult whiteflies per leaf). The major changes were recorded for
Cassava brown streak disease, recently reported in the region, for which a
significant increase was recorded, with not reports before 2012 to 70% - 80%
incidence in 2018 in the Ruzizi plain area (Uvira and Fizi). Molecular detection revealed a coexistence of both
two viruses, the cassava brown streak virus (CBSV) and Ugandan cassava brown
streak virus (UCBSV) in single and mixed infections. Co-infections
cassava mosaic and cassava brown streak diseases were frequently recorded
resulting in severe expression leaves’ symptoms and tuber yields’ losses.
Common pests and diseases considered as minor have drastically become serious
threat to cassava production by increasing both their incidence and severity
values. The cassava bacterial blight (20%), cassava green mite (20% - 70%),
cassava mealy bugs and cassava grasshoppers were recorded as a great challenge
in relation with an occurrence of long dry season resulting in four consecutive
dry months without rain. The high occurrence of CBSD on new CMD-resistant
varieties has enforced farmers to recover local CMD-susceptible varieties which
revealed a relative CBSD-tolerance and moderate yield losses. This need for
virus control is really challenging cassava crop in a region where the diseases pressure is high and people consume cassava
and its products seven days a week. Research gaps identified in the study are
the need for breeding new varieties with tolerance/resistance to both CMD and
CBSD viruses as well as the extensive use of rapid multiplex diagnostic tools
to ensure early diagnostic and availability of good quality planting material
at farmers’ level.