La relativité du facteur d'impact en recherche agronomique

Le facteur d'impact (= FI) d'une revue est un indicateur couramment utilisé pour l'évaluation de la production scientifique d'une équipe ou d'un organisme de recherche. La valeur de cet indicateur dépend de divers paramètres comme l'année de publication ou le champ disciplinaire (= subject category). De ce fait, les revues à facteur d'impact sont réparties par Thomson-ISI en 171 champs disciplinaires, une revue pouvant être répertoriée dans un ou plusieurs champs disciplinaires. Le Cirad, mène ses activités de recherche dans le domaine de l'agronomie tropicale. Le mode de représentation en box plots, ou boîtes à moustaches, appliqué aux 17 champs disciplinaires identifiés pour la majorité des articles publiés par le Cirad dans les revues à facteurs d'impact, permet d'illustrer la relativité de la valeur du facteur d'impact selon ces disciplines. Ce mode de représentation permet aussi: 1- d'identifier, pour certaines disciplines, des valeurs de FI hors normes, appelées outliers; 2- de montrer que la notoriété d'une revue, vue sous l'angle des FI, dépend du champ disciplinaire dans lequel celle-ci est étudiée, et 3- de constater que des comparaisons, hors champs disciplinaires, des valeurs brutes des FI peuvent conduire à des interprétations abusives. [Résumé d'auteur

Combining biological approaches to highlight the evolution of Musa complex

The diversity of the banana complex can be deciphered only by jointly characterizing the original wild species and their relatives, the primitive diploid forms and the triploid varieties. Sexuality, the primary source of diversity, is strongly disrupted in the cultivated varieties (sterility, parthenocarpy and vegetative propagation) and is relayed by human selection of punctuated mutations vegetatively maintained. Many biological tools illustrate peculiar facets of the diversity and their joint analysis enables an evolutionary reading of this diversity. The access to forms resulting from ancient events and vegetatively maintained is a valuable asset. We propose various assumptions in the structure of wild species, on the domestication of the edible diploids from hybrids between wild forms, on the direct ancestry of triploids from cultivated diploids, and on the ancient migrations. The comparison with data from archaeology, linguistics and human genetics will enable the validation, refinement and dating of the proposed domestication process. (Texte intégral

How eBSV polymorphism could enlighten BSV and banana evolution story?

The nuclear genome of banana plants is invaded by numerous viral sequences of banana streak viruses (BSV), a DNA virus belonging to the family Caulimoviridae. These integrations are mostly defective as a result of pseudogenisation driven by the host genome evolution. Conversely some named infectious, can release a functional viral genome following activating stresses. We characterized the infectious endogenous BSV (eBSV) for three BSV species (BSOLV, BSGFV and BSImV) present within the Musa balbisiana B genome of the seedy diploid Pisang Klutuk Wulung (PKW). Our aim is to study PKW-related BSV integrations among the diversity of the banana B genomes in order to retrace the evolutionary BSV and banana stories We extended on purpose the M. balbisiana diversity by the addition of interspecific hybrids with M. acuminata showing different levels of ploidy for the B genome (ABB, AAB, AB) of the banana sample in order to include unsampled or extinct M. balbisiana ressources. We also based the analysis referring to the two areas of sympatry between M. acuminata and M. balbisiana and the centers of origin for the most largely cultivated AAB cultivars. One was in India and the other one in East Asia going from Philippines to New Guinea (Perrier et al, 2009). We characterized the PKW-related eBSV allelic polymorphism using PCR markers (described in poster Galzi & Duroy et al.) and Southern blots on 77 accessions. We codified the results of Southern blot and PCR in order to calculate a common dissimilarity matrix and interpret the eBSV distribution. As a result, three dendrograms of PKW-related eBSV made with the Neighbor Joining (NJ) method on the 77 banana accessions, for each BSV species, are presented as well as one dendogram resulting of NJ analysis for the three BSV species all together . We show that the known phylogeny of banana accessions can enlighten the eBSV structure diversity and that eBSV polymorphisms can help to understand the particularly unresolved M. balbisiana diversity. An evolutionary scheme of BSV/eBSV banana evolution will be proposed. (Texte intégral

Risk assessment of spreading Banana streak viruses in the Dominican Republic through large scale cultivation of plantain cultivars and hybrids harbouring infectious eBSVs. [O.33]

Most cultivated plantains are interspecific cultivars or hybrids: they harbour Musa acuminata (A) genomes and Musa balbisiana (B) genomes which hosts infectious endogenous Banana streak virus sequences (eBSVs). Spontaneous infections can arise in plantains following activation of these sequences by biotic and abiotic stresses, such as tissue culture and temperature differences, while several mealybug species can transmit BSV horizontally. The level of activation of infectious eBSVs by tissue culture has been quantified for several plantain cultivars and hybrids [1, 2], but virtually nothing is known about activation levels under field conditions, thus preventing the assessment of the risk of spreading BSV through large scale cultivation of plantains. This question was addressed in the Dominican Republic, using the most widely cultivated plantain types in the country: triploid AAB cultivar Macho x Hembra (MxH) and tetraploid AAAB hybrid FHIA21. Both carry infectious eBSV alleles OL1 and GF7 of the two distinct BSV species BSOLV and BSGFV, respectively, but are devoid of infectious eBSVs of species BSIMV. Firstly, a nationwide survey was conducted throughout all Dominican banana growing areas. A total of 590 leaf samples of FHIA21 and MxH were collected from 36 locations reflecting the diversity of banana cultivation conditions in the country (temperature, irrigation, type of planting material, presence of mealybugs...). Samples were indexed for viral species BSOLV, BSGFV and BSIMV. Based on these results, two locations were selected for an in depth survey: 100 FHIA21 and 100 MxH leaf samples were collected from nearby plots in each location, and mealybug samples were also collected on sampled plants. All plant samples were indexed for viral species BSOLV, BSGFV and BSIMV, whereas total DNA was extracted from mealybugs and used to type mealybug species and search for BSV in mealybugs. Results from indexings and molecular analyses were used in a multifactorial statistical analysis taking into account environmental factors. Overall, results suggest that in the Dominican Republic, BSV infections in plantains MxH and FHIA21 result from the activation of infectious eBSVs rather than from horizontal transmission by mealybug vectors. They show that infection levels are significantly more important in FHIA21 than in MxH, highlighting the importance of genetic background in eBSV activation processes. Activation of infectious eBSVs was also assessed experimentally in FHIA21 and MxH. To this end, an experimental plot was set up under field culture conditions, using FHIA21 and MxH plants produced either by tissue culture or by suckers. Mealybugs and ants were controlled by insecticide treatment throughout the experiment, therefore ensuring that BSV infections could only arise from the activation of infectious eBSVs. All 484 plants of the plot were indexed regularly for BSV species BSOLV, BSGFV and BSIMV. Indexing results were used in a multifactorial statistical analysis, providing the first comparative risk assessment of spreading Banana streak viruses through cultivation of plantain cultivars and hybrids originating from tissue culture or suckers. (Résumé d'auteur