Bark essential oil of Cedrelopsis grevei from Madagascar: investigation of steam-distillation conditions.

The effect of the distillation time on the yield and chemical composition of the bark essential oil of Cedrelopsis grevei Baill. was investigated. Distillation kinetics were determined for three batches of bark sampled from two sites, i.e., Itampolo (batches IT1 and IT2) and Salary (SAL), located in a region in the south of Madagascar with characteristically large populations of C. grevei. The bark samples were subjected to steam distillation, and the essential oil was collected at 3-h intervals. The total yield (calculated after 14 h of distillation) varied from 0.9 to 1.7%, according to the batch tested. Moreover, the essential oils obtained were characterized by GC-FID and GC/MS analyses. During the course of the distillation, the relative percentages of the most volatile components (monoterpenes and sesquiterpene hydrocarbons) diminished progressively, whereas the least volatile ones (oxygenated derivatives) increased at a consistent rate. Principal component analysis (PCA) and agglomerative hierarchical clustering analysis (AHC) of the results, performed on 13 principal components, allowed distinguishing three chemical groups, corresponding to the three batches, irrespective of the distillation time. This indicated that the chemical variability currently observed with commercial samples is not mainly linked to the experimental conditions of the extraction process, as the distillation time did not significantly alter the chemical composition of the essential oils.

Comparing patterns and scales of plant virus phylogeography: Rice yellow mottle virus in Madagascar and in continental Africa.

Rice yellow mottle virus (RYMV) in Madagascar Island provides an opportunity to study the spread of a plant virus disease after a relatively recent introduction in a large and isolated country with a heterogeneous host landscape ecology. Here, we take advantage of field survey data on the occurrence of RYMV disease throughout Madagascar dating back to the 1970s, and of virus genetic data from ninety-four isolates collected since 1989 in most regions of the country to reconstruct the epidemic history. We find that the Malagasy isolates belong to a unique recombinant strain that most likely entered Madagascar through a long-distance introduction from the most eastern part of mainland Africa. We infer the spread of RYMV as a continuous process using a Bayesian statistical framework. In order to calibrate the time scale in calendar time units in this analysis, we pool the information about the RYMV evolutionary rate from several geographical partitions. Whereas the field surveys and the phylogeographic reconstructions both point to a rapid southward invasion across hundreds of kilometers throughout Madagascar within three to four decades, they differ on the inferred origin location and time of the epidemic. The phylogeographic reconstructions suggest a lineage displacement and unveil a re-invasion of the northern regions that may have remained unnoticed otherwise. Despite ecological differences that could affect the transmission potential of RYMV in Madagascar and in mainland Africa, we estimate similar invasion and dispersal rates. We could not identify environmental factors that have a relevant impact on the lineage dispersal velocity of RYMV in Madagascar. This study highlights the value and complementarity of (historical) nongenetic and (more contemporaneous) genetic surveillance data for reconstructing the history of spread of plant viruses.

Rice yellow mottle virus in Madagascar and in the Zanzibar Archipelago; island systems and evolutionary time scale to study virus emergence.

Rice yellow mottle virus (RYMV), of the genus Sobemovirus, is a major threat to rice cultivation in Africa. Long range transmission of RYMV, difficult to study experimentally, is inferred from a detailed analysis of the molecular diversity of the virus in Madagascar and in the Zanzibar Archipelago (Zanzibar and Pemba Islands; Tanzania) compared with that found elsewhere in Africa. A unique successful introduction of RYMV to Madagascar, which is ca. 400 km from mainland Africa, contrasted with recurrent introductions of the virus to the Zanzibar Archipelago, ca. 40 km from the East African coast. Accordingly, RYMV dispersal over distances of hundreds of kilometers is rare whereas spread of the virus over distances of tens of kilometers is relatively frequent. The dates of introduction of RYMV to Madagascar and to Pemba Island were estimated from three sets of ORF4 sequences of virus isolates collected between 1966 and 2011. They were compared with the dates of the first field detection in Madagascar (1989) and in Pemba Island (1990). The estimates did not depend substantially on the data set used or on the evolutionary model applied and their credible intervals were narrow. The estimated dates are recent - 1978 (1969-1986) and 1985 (1977-1993) in Madagascar and in Pemba Island, respectively - compared to the early diversification of RYMV in East Africa ca. 200 years ago. They predated by 5-10 years the first field detections in these islands. The interplay between virus sources, rice cultivation and long range dispersal which led to RYMV emergence and spread is enlightened.