Contribution of cassava-maize-common beans inter-cropping system to the management of cassava mosaic disease and its vector

Cassava mosaic disease (CMD) is reported as the most important constraint on cassava in Sub-Saharan Africa. The understanding of the disease epidemiology, the genetic diversity of the virus and its vector is a key factor for the disease management. In this study, cropping system associating cassava, common beans (Phaseolus vulgaris) and maize, the most frequent cassava cropping system in Eastern DR Congo, was investigated to understand the disease characteristics and existing interactions within this pathosystem: cassava mosaic begomoviruses (CMBs), cassava and non-cassava plants, Bemisia tabaci population and agro-ecosystems in which they are found. Different geographic locations mainly depending on the altitude levels showed a significant influence on CMD incidence and severity, and whitefly population. CMD and its vector pressure were high in low altitude, but significant decrease was observed in intercropped fields. Under high epidemic pressure, respective decreases of 19% and of 33.3% were recorded on disease incidence and whitefly population. Only two CMBs (ACMV and EACMV-UG) were detected both in cassava plants and in whiteflies collected on cassava and other plant species. In contrast, no CMBs were detected in non-cassava associated plants. Bemisia tabaci characterization based on MtCOI sequences analysis revealed the presence of a single haplotype close to Ug1, irrespective of the plant species on which the insects were collected. The low diversity of the CMBs and whitefly population combined with the impact of local intercropping system cassava, common beans and maize are discussed, underlining the interest of the other ways of CMD management besides crop resistance strategies.