East African cassava mosaic-like viruses from Africa to Indian ocean islands: molecular diversity, evolutionary history and geographical dissemination of a bipartite begomovirus

Abstract

BackgroundCassava (Manihot esculenta) is a major food source for over 200 million sub-Saharan Africans. Unfortunately, its cultivation is severely hampered by cassava mosaic disease (CMD). Caused by a complex of bipartite cassava mosaic geminiviruses (CMG) species (Family: Geminivirideae; Genus: Begomovirus) CMD has been widely described throughout Africa and it is apparent that CMG's are expanding their geographical distribution. Determining where and when CMG movements have occurred could help curtail its spread and reveal the ecological and anthropic factors associated with similar viral invasions. We applied Bayesian phylogeographic inference and recombination analyses to available and newly described CMG sequences to reconstruct a plausible history of CMG diversification and migration between Africa and South West Indian Ocean (SWIO) islands.ResultsThe isolation and analysis of 114 DNA-A and 41 DNA-B sequences demonstrated the presence of three CMG species circulating in the Comoros and Seychelles archipelagos (East African cassava mosaic virus, EACMV; East African cassava mosaic Kenya virus, EACMKV; and East African cassava mosaic Cameroon virus, EACMCV). Phylogeographic analyses suggest that CMG’s presence on these SWIO islands is probably the result of at least four independent introduction events from mainland Africa occurring between 1988 and 2009. Amongst the islands of the Comoros archipelago, two major migration pathways were inferred: One from Grande Comore to Mohéli and the second from Mayotte to Anjouan. While only two recombination events characteristic of SWIO islands isolates were identified, numerous re-assortments events were detected between EACMV and EACMKV, which seem to almost freely interchange their genome components.ConclusionsRapid and extensive virus spread within the SWIO islands was demonstrated for three CMG complex species. Strong evolutionary or ecological interaction between CMG species may explain both their propensity to exchange components and the absence of recombination with non-CMG begomoviruses. Our results suggest an important role of anthropic factors in CMGs spread as the principal axes of viral migration correspond with major routes of human movement and commercial trade. Finer-scale temporal analyses of CMGs to precisely scale the relative contributions of human and insect transmission to their movement dynamics will require further extensive sampling in the SWIO region.

Divergent evolutionary and epidemiological dynamics of cassava mosaic geminiviruses in Madagascar

“…7): a finding which confirms the results of a previous study [32]. Our results additionally infer that the presence of EACMV-like viruses in Madagascar is the consequence of three to four independent introduction events.…”

“…Interestingly, our results confirm the major differences in the composition of CMG populations between Madagascar and the islands of the nearby Comoros archipelago where EACMV along with EACMKV are the dominant CMG species [32]. Despite extensive sampling, neither SACMV nor ACMV have ever been found in the Comoros.…”

“…Several studies of CMG diversity and evolution have been conducted in East Africa [13, 19, 33], West Africa [18, 19] and on the South West Indian Ocean islands [32]. Whereas these studies have revealed the extensive dissemination of different CMG species across Africa and the SWIO islands, each study focused primarily on only a small subset of the known CMG species: a factor which has made it difficult to compare the spatial distributions and evolutionary characteristics of the different CMGs.…”

Recent Biotechnological Advances in the Improvement of Cassava

“…With the emergence of new molecular and sequencing capabilities, CMGs have been shown to exhibit considerable sequence and biological differences and so far, 11 species have been described in the cassava growing regions of African and the Indian subcontinent [28] and some of these viruses co-infect the same plant resulting in a synergistic interaction, characterized by severe symptoms (Figure 3). Interestingly, cassava was introduced in Africa from South America [29], yet CMGs are not found in South America and therefore these viruses are likely recent descendants of geminiviruses adapted to indigenous uncultivated African plant species [30]. The problem of CMGs has been compounded by the emergence, in eastern Africa, of cassava brown streak disease (CBSD), which is caused by cassava brown streak viruses (CBSVs (Family, Potyviridae: Genus, Ipomovirus).…”

Molecular-assisted selection for resistance to cassava mosaic disease in Manihot esculenta Crantz

“…CMD is transmitted by Bemisia tabaci (Genn) biotype B at different stages, as well as by the use of infected propagation material and cutting tools that are commonly used in cassava cultivation (De Bruyn et al, 2012). The damage that is caused by this disease can reach 100 % of the crop (Thresh et al, 1994), with estimated production losses of approximately $ 440 million annually in Africa (Thresh et al, 1997).…”