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Doungous O.,Ekona Regional Research Center | Kalendar R.,University of Helsinki | Adiobo A.,Ekona Regional Research Center | Schulman A.H.,University of Helsinki | Schulman A.H.,Luke Natural Resources Institute Finland
Euphytica | Year: 2015

Retrotransposon-based molecular markers were applied for the first time within the genera Xanthosoma and Colocasia to assess intraspecific variability among 27 accessions of cocoyam (Xanthosoma sagittifolium) and taro (Colocasia esulenta). Retrotransposons were isolated and sequenced; long terminal repeat (LTR) primers were designed to obtain inter-retrotransposon amplified polymorphism (IRAP) fingerprints. A set of six chosen LTR primers yielded 433 reproducible bands across 20 X. sagittifolium samples. Out of the 433 bands, 400 fragments (92 %) were polymorphic. In seven C.esculenta accessions, the six primers amplified a total of 354 reproducible, informative data points, of which 285 (80.5 %) were polymorphic. Cluster analysis placed all the accessions in two groups according to their species. The accessions of X. sagittifolium were further divided into two subgroups corresponding to their ploidy level. Moreover, the genetic variability accessed by IRAP markers allowed separation of X. sagittifolium and C. esculenta accessions according to their type and botanical variety respectively. The results suggest that retrotransposon activity continued after Xanthosoma speciation. The data and approach provides a basis for better germplasm management, future systematic studies and genetic improvement, as well as for exploration of the role of retrotransposons in cocoyam and taro polyploid formation and genome dynamics. © 2015, Springer Science+Business Media Dordrecht.

Ehabe E.E.,Ekona Regional Research Center | Frederic B.,CIRAD - Agricultural Research for Development
Journal of Rubber Research | Year: 2011

In a suitable organic solvent, Hevea natural rubber (NR) disintegrates into an insoluble gel phase (macrogel) and a sol phase consisting of polyisoprene chains with micro-aggregates (microgel). Studies on Hevea microgel following the advent of its quantitation by steric exclusion chromatography (SEC) are quite recent. In this study, transesterification of NR favoured macrogel elimination with unclear effects on the microgel. The NR's structure and the relative gel quantities varied in solution (depending on the solvents used) and during transesterification to produce substantial quantities of low-to-average molar mass chains (probably from the macrogel and/or the microgel fraction). The macrogel broke down equally to microgel. This microgel, representing 25%-30% Hevea rubber, remained insensitive to transesterification. The NR's structure was made up essentially of variably-sized membranedelimited entities. On dissolution, these entities were denatured and through this liberated more or less branched polyisoprene chains, as well as some microgel and macrogel.

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