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Distribution and diversity of viruses infecting yams (Dioscorea spp.) in Cameroon.

ABSTRACT: Yam (Dioscorea spp.) is an important food crop cultivated for its edible tubers in Cameroon. Surveys were conducted in Cameroon to determine the incidence and severity of yam mosaic disease and associated viruses in 124 yam farms in four agro-ecological zones in 2014 and 2016. Dioscorea rotundata, D. cayenensis, D. alata, D. Dumetorum and D. bulbifera were most frequently detected yam species in the fields. Symptoms of virus disease were observed on 81.5% of the farms surveyed and the disease incidence ranged from 0 to 96.7%, with an overall mean of 26.5%. Mean symptom severity estimated using a numerical rating scale of 1-5, ranged from 2 to 4.1, with an overall mean of 2.6. Representative set of leaf samples collected from farmers' fields were tested for three viruses known to cause yam mosaic disease in West Africa, viz., Yam mosaic virus (YMV), Yam mild mosaic virus (YMMV) and Cucumber mosaic virus (CMV), using multiplex RT-PCR. YMV and YMMV were detected in 220 (37.2%) of the 591 samples tested and 75% of the farms surveyed. None of the samples tested positive to CMV. Phylogenetic analysis based on the coat protein sequencing of 27 YMV isolates clustered these isolates into three phylogenetic groups. This study demonstrated high prevalence of mosaic disease in yam fields and YMV as main causal agent. Knowledge generated in this study will be useful to augment diagnostic tools and yam mosaic disease control with a view to improve on yam production in Cameroon.

SUBMITTER: Azeteh IN

PROVIDER: S-EPMC6917680 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:UnlabelledThe functional diversity of eukaryotic viruses infecting a single host strain from seawater samples originating from distant marine locations is unknown. To estimate this diversity, we used lysis plaque assays to detect viruses that infect the widespread species Ostreococcus lucimarinus, which is found in coastal and mesotrophic systems, and O. tauri, which was isolated from coastal and lagoon sites from the northwest Mediterranean Sea. Detection of viral lytic activities against O. tauri was not observed using seawater from most sites, except those close to the area where the host strain was isolated. In contrast, the more cosmopolitan O. lucimarinus species recovered viruses from locations in the Atlantic and Pacific Oceans and the Mediterranean Sea. Six new O. lucimarinus viruses (OlVs) then were characterized and their genomes sequenced. Two subgroups of OlVs were distinguished based on their genetic distances and on the inversion of a central 32-kb-long DNA fragment, but overall their genomes displayed a high level of synteny. The two groups did not correspond to proximity of isolation sites, and the phylogenetic distance between these subgroups was higher than the distances observed among viruses infecting O. tauri. Our study demonstrates that viruses originating from very distant sites are able to infect the same algal host strain and can be more diverse than those infecting different species of the same genus. Finally, distinctive features and evolutionary distances between these different viral subgroups does not appear to be linked to biogeography of the viral isolates.ImportanceMarine eukaryotic phytoplankton virus diversity has yet to be addressed, and more specifically, it is unclear whether diversity is connected to geographical distance and whether differential infection and lysis patterns exist among such viruses that infect the same host strain. Here, we assessed the genetic distance of geographically segregated viruses that infect the ubiquitous green microalga Ostreococcus. This study provides the first glimpse into the diversity of predicted gene functions in Ostreococcus viruses originating from distant sites and provides new insights into potential host distributions and restrictions in the world oceans.

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Distribution and diversity of viruses infecting yams (Dioscorea spp.) in Cameroon.

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