Search

In this study, three strains of Trypanosoma cruzi were isolated at the same time and in the same endemic region in Mexico from a human patient with chronic chagasic cardiomyopathy (RyC-H); vector (Triatoma barberi) (RyC-V); and rodent reservoir (Peromyscus peromyscus) (RyC-R). The three strains were characterized by multilocus enzyme electrophoresis, random amplified polymorphic DNA, and by pathological profiles in experimental animals (biodemes). Based on the analysis of genetic markers the three parasite strains were typed as belonging to T. cruzi I major group, discrete typing unit 1. The pathological profile of RyC-H and RyC-V strains indicated medium virulence and low mortality and, accordingly, the strains should be considered as belonging to biodeme Type III. On the other hand, the parasites from RyC-R strain induced more severe inflammatory processes and high mortality (> 40%) and were considered as belonging to biodeme Type II. The relationship between genotypes and biological characteristics in T. cruzi strains is still debated and not clearly understood. An expert committee recommended in 1999 that Biodeme Type III would correspond to T. cruzi I group, whereas Biodeme Type II, to T. cruzi II group. Our findings suggest that, at least for Mexican isolates, this correlation does not stand and that biological characteristics such as pathogenicity and virulence could be determined by factors different from those identified in the genotypic characterization.

In Mexico, Triatoma longipennis (Usinger), Triatoma picturata (Usinger), and Triatoma pallidipennis (Stal), primary Chagas disease vector species of the phyllosoma complex, were analyzed by randomly amplified polymorphic DNA (RAPD). Sixteen decametric primers resolved individual profiles not identical, but partially discriminative between species. Analysis based on pairwise presence/absence comparisons between the three species was performed using three primers and two outgroup species Triatoma infestans (Klug) and Triatoma barberi (Usinger). Fifty-three bands in total were scored, although only two bands were constant among the three phyllosoma complex species. Two other bands were constant only for T. longipennis and T. picturata together, and not present in T. pallidipennis. Neighbor Joining tree and the multiple correspondence analysis discriminated T. pallidipennis clearly from the other two species, although there was overlap between T. longipennis and T. picturata. The results indicate a close relationship between the studied species and support the hypothesis of their recent evolution. The suitability of RAPD to discern populations within the species is discussed.

Trypanosome stocks isolated from bats (Chiroptera) and belonging to the subgenus Schizotrypanumwere analyzed by multilocus enzyme electrophoresis (MLEE) at 22 loci, random amplified polymorphic DNA (RAPD) with 14 primers and/or cytochrome b nucleotide sequence. Bat trypanosomes belonged to the species Trypanosoma cruzi marinkellei(10 stocks), Trypanosoma dionisii(four stocks) and Trypanosoma vespertilionis (three stocks). One T. rangeli stock and seven stocks of T. cruzi sensu stricto, the agent of Chagas disease, were included for comparison. The homology of several RAPD fragments shared by distinct species was verified by hybridization. The sequence of a 516-nucleotide portion of the maxicircle-encoded cytochrome b (CYb) coding region was determined in representative stocks of the species under study. Phylogenetic analysis of the data confirmed the previous taxonomic attribution of these bat trypanosomes based on biological, epidemiological and ecological features. However, a new finding was that within T. cruzi marinkellei two major subdivisions could be distinguished, T.c.m. I, found in the spear-nose bats Phyllostomus discolorand Phyllostomus hastatus, and T.c.m. II, from P. discolor .I n addition, the T. c. marinkellei ‘Z’ stock from a short-tailed bat (Carollia perspicillata) was distantly related to these two subdivisions, and the monophyly of T. c. marinkelleiis unclear based on the present data. Based on the present sample, the European species T. dionisii and T. vespertilionis appeared to be more homogeneous. RAPD andCYb data both suggested the monophyly of a group composed of T. cruzi and the two major subdivisions of T. cruzi marinkellei. This study shows that MLEE, RAPD andCYb can be used for taxonomic assignment and provide valuable phylogenetic information for strains and taxa within the subgenus Schizotrypanum. An evolutionary scenario in which the broad host-range parasite T. cruzi would be derived from a bat-restricted trypanosome ancestor is discussed. © 2002 Elsevier Science B.V. All rights reserved.

We studied the population genetic structure of 360 and 1247 adult Schistosoma mansoni using seven microsatellite and seven random amplified polymorphic DNA (RAPD) markers, respectively. Parasites were collected from their natural definitive host Rattus rattus in Guadeloupe (West Indies). We found a sex-specific genetic structure, a pattern never before reported in a parasitic organism. Male genotypes were more randomly distributed among rats than female genotypes. This interpretation was consistent with a lower differentiation between hosts for males relative to females, the higher genetic similarity between females in the same host and the observed local (i.e. within-individual-host) differences in allele frequencies between the two sexes. We discuss our results using ecological and immunological perspectives on host-parasite relationships. These results change our view on the epidemiology of schistosomiasis, a serious disease affecting humans in African and American intertropical zones.

Three randomly amplified polymorphic DNA (RAPD) markers, OPA-12420, OPB-061200 and OPA-01700, species specific to the root-knot nematode species Meloidogyne arenaria, M. incognita and M. javanica respectively, were identified. After sequencing these RAPD-PCR products, longer primers of 18 to 23 nucleotides were designed to complement the terminal DNA sequences of the DNA fragments. This resulted in three pairs of species specific primers that were used to amplify the sequence characterised amplified regions (SCARs). The developed sets of SCAR primers were successfully used in straightforward, fast and reliable PCR assays to identify M. incognita, M. javanica and M. arenaria. The length variant SCAR markers can be amplified from DNA from egg masses, second stage juveniles and females. This species identification technique is therefore independent of the nematode's life cycle stage. Moreover the SCAR-PCR assay was successfully applied using DNA extracts from infested plant material. The method has potential to be optimised for routine practical diagnostic tests facilitating the control of these economically important pest organisms. Identification de Meloigyne incognita, M. javanica et M. arenaria au moyen de l'amplification de régions de séquences caractéristiques (SCAR) par une technique PCR - Trois marqueurs d'ADN polymorphique amplifiée au hasard (RAPD) OPA-12420, OPB-O61200 et OPA-OI700, respectivement spécifiques des espèces de nématodes Meloidogyne arenaria, M. incognita et M. javanica, ont été identifiés. Après le séquençage de ces produits RAPD-PCR, les amorces les plus longues de 18 à 23 nucléotides ont été choisies pour compléter les séquences terminales d'ADN des fragments d'ADN. Cela a conduit à trois paires d'amorces spécifiques de l'espèce, utilisées pour amplifier les régions des séquences caractéristiques (SCAR). Les lots d'amorces SCAR mis au point ont été utilisés avec succès lors d'essais directs, rapides et surs pour identifier M. incognita, M. javanica et M. arenia. Les marqueurs peuvent être amplifiés à partir de l'ADN des masses d'oeufs, des juvéniles de deuxième stade ou des femelles. Cette technique d'identification spécifique est donc indépendante des différents états de développement du nématode. De plus la technique SCAR-PCR a été appliquée avec succès à l'ADN extrait du matériel végétal infesté. Cette méthode présente des potentialités d'amélioration permettant d'envisager des tests pratiques d'identification de routine, facilitant ainsi le contrôle de ces parasites économiquement importants.

Nous avons étudié une collection de 76 nouveaux isolats bactériens de nodules obtenus par piégeage sur plantes d'Acacia tortilis subsp. raddiana in vitro, inoculées avec des suspensions de sols prélevés dans divers sites au nord (Tunisie) et au sud (Sénégal, Mauritanie) du Sahara, en comparaison avec 54 souches de références. L'analyse des nouveaux isolats par RAPD et SDS-PAGE a montré une grande diversité taxonomique parmi les isolats d'A. tortilis subsp. raddiana. En effet, bien que toutes les souches puissent être qualifiées de « rhizobium à croissance rapide », elles se répartissent en au moins 9 groupes différents, dont plusieurs ne correspondent à aucun des groupes de rhizobia déjà décrits. Aucune relation entre la position taxonomique des souches, leur origine géographique, les conditions édaphiques ou la profondeur d'isolement n'a pu être établie. La caractérisation symbiotique des souches d'A. tortilis subsp. raddiana a, au contraire, montré une grande homogénéité des caractéristiques symbiotiques majeures. Toutes les souches nodulent également A. Senegal, Prosopis julifora et Leucaena leucocephala, qui constituent avec A. tortilis subsp. raddiana un groupe d'inoculation. L'analyse des profils chromatographiques des facteurs Nod (FN) d'une quinzaine de souches réparties dans les différents groupes taxonomiques montre qu'ils sont très similaires. L'homogénéité structurale des FN des souches d'A. tortilis subsp. raddiana a été confirmée par la détermination de la structure des FN de quelques souches représentatives. Cette étroite relation entre FN et plante d'isolement/spectre d'hôte indépendamment de la taxonomie des souches suggère l'existence d'une forte pression de sélection de la part de la plante hôte et confirme nos observations précédentes, à savoir que les facteurs Nod sont de bons indicateurs du potentiel de nodulation d'un rhizobium donné. We studied a collection of 76 new bacterial isolates from nodules developed on Acacia tortilis subsp. raddiana plants inoculated in vitro with soil suspensions harvested in different sites in North (Tunisia) and South (Senegal, Mauritania) parts of Sahara. RAPD and SDS-PAGE analyses in comparison with 54 reference strains from diverse origins showed great taxonomie diversity among the new isolates. All of them are fast-growing and form at least 9 different groups, several of which could correspond to undescribed groups. No relationship could be established between taxonomie groups, geographical origin (North/South of Sahara) of the strains, edaphic conditions, or depth of soil sampling (down to - 32 m). Opposite to their taxonomie diversity, the new isolates share identical main symbiotic properties. All strains nodulating A. tortilis subsp. raddiana can also nodulate Prosopis juliflora, Acacia Senegal and Leucaena leucocephala, these four plants then constituting a cross-inoculation group. By thin-layer chromatography, we showed that 20 A. tortilis subsp. raddiana strains, representative of the different taxonomie groups, share very similar Nod factor (NF) profiles, independently from their geographical origins. NF structure homogeneity was confirmed by NF structure determination of some representative strains. The consistency between NF and plant of isolation/nodulation spectrum, independently of the taxonomie position of the strains suggests a high selection pressure from the plant, and confirms our previous observations that NF are good markers for predicting the nodulation potential of a given rhizobial strain.

In this study, we successfully cryopreserved cotyledonary somatic embryos of diploid and triploid Arachis pintoi cytotypes using the encapsulation-dehydration technique. The highest survival rates were obtained when somatic embryos were encapsulated in calcium alginate beads and precultured in agitated (80 rpm) liquid establishment medium (EM) with daily increasing sucrose concentration (0.50, 0.75, and 1.0 M). The encapsulated somatic embryos were then dehydrated with silica gel for 5 h to 20% moisture content (fresh weight basis) and cooled either rapidly (direct immersion in liquid nitrogen, LN) or slowly (1ºC min-1 from 25ºC to -30ºC followed by immersion in LN). Beads were kept in LN for a minimum of 1 h and then were rapidly rewarmed in a 30ºC water-bath for 2 min. Finally, encapsulated somatic embryos were post-cultured in agitated (80 rpm) liquid EM with daily decreasing sucrose concentration (0.75 and 0.5 M) and transferred to solidified EM. Using this protocol, we obtained 26% and 30% plant regeneration from cryopreserved somatic embryos of diploid and triploid cytotypes. No morphological abnormalities were observed in any of the plants regenerated from cryopreserved embryos and their genetic stability was confirmed with 10 isozyme systems and nine RAPD profiles. Fil: Rey, Hebe Yolanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina; Fil: Faloci, Mirta Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina; Fil: Medina, Ricardo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina; Fil: Dolce, Natalia Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina; Fil: Engelmann, Florent. Centre National de la Recherche Scientifique. Institut de Recherche Pour Le Developpement; Francia; Fil: Mroginski, Luis Amado. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina

La Quinua (Chenopodium quinoa Willd.) es un pseudocereal originario de los Andes importante para la seguridad alimentaria de los pequeños agricultores, así como para la producción comercial. Recientemente, se ha afirmado que la erosión genética en Bolivia podría ser el resultado de la marginación del cultivo en el Altiplano norte y de su estandarización comercial en el Altiplano sur. El objetivo de este estudio fue cuantificar la estructura jerárquica de la variación genética presente en ocho poblaciones de quinua, que corresponden a formas cultivadas y formas silvestres, representativas del Altiplano y de valles interandinos de Bolivia. El análisis con marcadores polimórficos de ADN muestra que la quinua tiene una fuerte estructura de población y una alta variación intra-población. Un efecto de la estructura geográfica de las poblaciones se evidencia, debido al aislamiento de las poblaciones, no simplemente ligado a las distancias, pero más probablemente a las barreras climáticas y orográficas presentes en la zona estudiada. La estructura de la población es también reforzada por los intercambios limitados de semillas entre agricultores, revelado por entrevistas realizadas en campo. esta estructura de poblaciones aparece relacionada con las tres grandes zonas biogeográficas: la del norte y centro del Altiplano, valles interandinos y el Altiplano sur. La diversidad genética intrapoblacional fue mayor que la esperada para una especie principalmente autógama, y mayor que lo reportado en estudios anteriores en base a colecciones de germoplasma. Estos resultados se comentan en vista de los conocimientos actuales sobre la filogenia y la biología reproductiva de la especie, y sus implicaciones frente al manejo de los recursos genéticos pueden ser discutidas. (résumé d'auteur)

Quinoa (Chenopodium quinoa Willd.) is a pseudocereal originated from the Andes important for small farmers' food security as well as for commercial production. Recently, it has been claimed that in Bolivia genetic erosion could result from the marginalization of the crop in the north and from its commercial standardization in the south. The aim of this study was to quantify the hierarchical structure of the genetic variation present in eight quinoa field populations, consisting of cultivated and weedy individuals, representative of the altiplano and interandean valleys of Bolivia. Randomly amplified polymorphic DNA markers show that quinoa has a strong population structure and a high intra-population variation. An effect of geographical structure of the populations was highlighted, due to population isolation, not simply linked to distance but more probably to climatic and orographic barriers present in the studied zone. The population structure is also reinforced by the limited seed exchanges among farmers as revealed by field interviews. This population structure appears related to three major biogeographic zones: the northern and central altiplano, the interandean valley, and the southern Salar. Intrapopulation genetic diversity was higher than that expected for a mainly autogamous species, and higher than that reported in anterior studies based on germ.plasm collections. These results are commented in view of current knowledge on phylogeny and reproductive biology of the species, and their implications regarding genetic resources management are discussed.

Trypanosoma cruziis thought to undergo predominant clonal evolution, as determined by population genetics studies. However, this model does not exclude occasional recombination, which existence is strongly suggested by several recent studies. We sequenced a portion of the maxicircle cytochrome b (CYb) gene and of the nuclear rRNA promoter region from representative strains of six T. cruzi genetic lineages isolated from anthroponotic environments and man (lineages IIb, IId and IIe), sylvatic environments (lineages IIa and IIc) or both (lineage I). Phylogenetic analyses based on the two genes were incongruent. Remarkably, in lineage IIe, CYb and rRNA sequences were very closely related to those of lineages IIc and IIb, respectively. One stock of lineage IId showed rRNA sequence heterogeneity, with both IIb-like and IIc-like copies. Analysis of the size variation of six distinct pairs of putative homologous chromosomes revealed a bimodal distribution of chromosomal sizes across T. cruzi. Notably, stocks of lineages IId and IIe had several chromosomal pairs distributed in distinct modes, with the corresponding modes individually found in lineages IIb and IIc. Together, these data indicate the origin of lineages IId and IIe by hybridization between representatives of lineages IIb and IIc. CYb and rRNA sequences clustered into three and four major lineages, respectively. Data were in agreement with the distinction of six genetic lineages, but not with their proposed grouping into two primary lineages, as lineage II was not monophyletic. Based on a CYb substitution rate of 1% per million years (Myr), the major lineages are estimated to have diverged around 10 million years ago. © 2002 Elsevier Science B.V. All rights reserved.

Coffea canephora# possede l'une des aires de repartition les plus larges du sous-genre #Coffea# : elle s'etend d'ouest en est, de la Guinee au Soudan et, du nord au sud, du Cameroun a l'Angola. La conservation a long terme de cette espece s'effectue en champs a cause du comportement peu orthodoxe de ses graines lors de leur stockage. La premiere analyse de la diversite genetique de cette espece a ete realisee a partir du polymorphisme enzymatique. L'utilisation des marqueurs moleculaires est recente et les resultats presentes dans ce chapitre constituent les premieres donnees sur la variabilite moleculaire de #C. canephora#. L'analyse de la diversite agromorphologique ne permet pas de reveler une forte structuration de l'espece. A l'aide des locus isoenzymatiques discriminant les groupes guineen et congolais, un schema de selection recurrente reciproque de #C. canephora# fonde sur l'utilisation de ces deux groupes a ete propose et son efficacite a ete validee par la suite, ce qui confirme qu'il est important de connaitre la structure de la diversite pour exploiter au mieux les ressources genetiques. Les resultats de l'etude sur les marqueurs moleculaires devraient permettre d'ameliorer ce schema de selection. Un certain nombre de recommandations pour assurer une meilleure gestion #ex situ# des ressources genetiques est avance

Rice progenies used for the construction of genetic maps permit exhaustive identification and characterization of resistance genes present in their parental cultivars. We inoculated a rice progeny derived from the cross IR64 x Azucena with different Magnaporthe grisea isolates that showed differential responses on the parental cultivars. By QTL mapping, nine unlinked loci conferring resistance to each isolate were identified and named Pi-24( t) to Pi-32( t). They could correspond to nine specific resistance genes. Five of these resistance loci (RLs) were mapped at chromosomal locations where no resistance gene was previously reported, defining new resistance genes. Using degenerate primers of the NBS (nucleotide binding site) motif found in many resistance genes, two resistance gene analogues (RGAs) IR86 and IR14 were identified and mapped closely to two blast RLs (resistance identified in this study, i.e. Pi-29(t) and Pi-30(t) respectively). These two RLs may correspond to the Pi-11 and Pi-a blast resistance genes previously identified. Moreover, the ir86 and ir14 genes have been identified "in silico" on the indica rice cultivar 93-11, recently sequenced by Chinese researchers. Both genes encodes NBS-LRR-like proteins that are characteristics of plant-disease resistance genes.

Microsatellites or simple sequence repeats (SSR) were used to assess polymorphism among 16 Coffea arabica and four Coffea canephora accessions, and to identify DNA introgression fragments from C. canephora in four C. arabica lines. Thirty-one primer pairs allowed for the identification of 92 polymorphic alleles distributed over 37 loci. The C. arabica accessions derived from the genetic bases 'Typica' and 'Bourbon' were grouped separately according to their genetic origin. Two genotypes derived from a spontaneous hybrid (C. arabica x C. canephora) were classified with the C. canephora accessions from Central Africa. Coffea canephora from West Africa were separated from the other accessions studied. Four alleles related to introgression (i.e. present in C. canephora and introgressed lines, and absent in C. arabica) were identified. The SSR markers were used successfully for characterization of a particular cultivar ('Veranero') from Costa Rica, which is known for its late maturity. (Resume d'auteur)

We have analyzed 75 isolates of Plasmodium falciparum , collected in Venezuela during both the dry (November) and rainy (May–July) seasons, with a range of genetic markers including antigen genes and 14 random amplified polymorphic DNA (RAPD) primers. Thirteen P. falciparum stocks from Kenya and four other Plasmodium species are included in the analysis for comparison. Cross-hybridization shows that the 14 RAPD primers reveal 14 separate regions of the parasite's genome. The P. falciparum isolates are a monophyletic clade, significantly different from the other Plasmodium species. We identify three RAPD characters that could be useful as “tags” for rapid species identification. The Venezuelan genotypes fall into two discrete genetic subdivisions associated with either the dry or the rainy season; the isolates collected in the rainy season exhibit greater genetic diversity. There is significant linkage disequilibrium in each seasonal subsample and in the full sample. In contrast, no linkage disequilibrium is detected in the African sample. These results support the hypothesis that the population structure of P. falciparum in Venezuela, but not in Africa, is predominantly clonal. However, the impact of genetic recombination on Venezuelan P. falciparum seems higher than in parasitic species with long-term clonal evolution like Trypanosoma cruzi , the agent of Chagas' disease. The genetic structure of the Venezuelan samples is similar to that of Escherichia coli , a bacterium that propagates clonally, with occasional genetic recombination.

The colonization dynamics of the black truffle in an artificial field were assessed through analyses of microsatellite and RAPD markers. The truffle field was composed of three tree species and mycelial inoculum of three different origins, and was monitored for the first three years of truffle production. We found very low levels of genetic diversity. Isolation by distance was detected only at the between-tree level. This could be interpreted as local colonization around each tree facilitated by the presence of the tree root system. At the larger spatial scale of the European range, the absence of isolation by distance corroborates the hypothesis of an impact of glaciation on genetic variation, followed by rapid postglaciation demographic expansion. In addition, genetic variation of harvested truffles was explained by neither inoculation origin, nor tree species. Our study questions the real impact of man-made inoculation of tree root systems with fungal mycelia.

DOI: 10.1139/gen-44-4-589; International audience

Six discrete phylogenetic lineages were recently identified in #Trypanosoma cruzi$, on the basis of multifocus enzyme electrophoresis and random amplified polymorphic DNA (RAPD) characterisation. The objective of the present study was to develop specific PCR-based markers for the identification of each of the six lineages. Eighty-seven #T. cruzi$ stocks representative of all the lineages were characterised by RAPD with three primers, resulting in the identification of three fragments that were specifically amplified in the given sets of lineages. After cloning and sequencing these fragments, three pairs of sequenced-characterised amplified region (SCAR) primers were designed. After PCR amplification using the SCAR primers, the initial polymorphism was retained either as the presence or absence of amplification, or as size variation between the PCR products. Although most PCR products, taken individually, were distributed across several lineages, the combination of the three SCAR markers resulted in characteristic patterns that were distinct in the six lineages. Furthermore, #T. cruzi$ lineages were distinguished from #Trypanosoma rangeli$, #T. cruzi marinkellei$ and #T. cruzi$-like organisms. The excellent correspondence of these new PCR markers with the phylogenetic lineages, allied with their sensitivity, make them reliable tools for lineage identification and strain characterisation in #T. cruzi$. The approach described here could be generalised to any species of microorganism harbouring clear-cut phylogenetic subdivisions. (Résumé d'auteur)

A sylvatic #Triatoma infestans$ DM (dark morph) population detected in the Bolivian Chaco was characterized and compared with various domestic ones. The degree of differentiation of DM was clearly within the #T. infestans$ intra-specific level. Nevertheless marked chromatic and morphometric differences as well as differences in antennal pattern, chromosome banding and randomly amplified polymorphic DNA support the hypothesis of a distinct population. Continuous exchange of insects between wild and domestic habitats seems unlikely in the Chaco. (Résumé d'auteur)

La Trypanosomose Humaine Africaine (THA) est une affection parasitaire due à un protozoaire de l'espèce #Trypanosoma brucei$. La complexité de l'évolution clinique de la maladie est fréquemment évoquée. Lors de cette étude en Côte d'Ivoire, l'origine de cette complexité a été recherchée à la fois chez le parasite par l'étude de la diversité génétique au sein de #Trypanosoma brucei$ spp. et chez l'hôte chez lequel un susceptibilité individuelle à l'infection est suspectée. Deux enquêtes ont été nécessaires pour mener à bien ces recherches, la première consistant à étudier l'existence d'associations entre la diversité génétique des trypanosomes et la diversité des formes cliniques qu'ils occasionnent, et la deuxième consistant en un suivi à long terme de sujets refusant le traitement. Les techniques de caractérisation des trypanosomes ont mis en évidence un important monomorphisme génétique au sein des souches circulant en Côte d'Ivoire alors que l'étude clinique a confirmé une grande diversité de tableaux et d'évolutions cliniques. Cependant, les taux d'isolement observés ont été particulièrement faibles, pouvant entraîner un biais dans notre échantillonage de parasites, mais quoiqu'il en soit, l'existence d'une susceptibilité individuelle à l'infection semble devoir être prise en considération et devra être étudiée par des travaux complémentaires. (Résumé d'auteur)

A survey of natural ecotopes of #Triatoma infestans$ dark morph and other triatomine sylvatic species was performed in an uninhabited area of the Bolivian Chaco. Among the 321 triatomines collected by light trapping, only 4 #T. infestans$ dark morph specimens were identified. Predominant flying species were #T. guasayana$ and #T. sordida$ group 2 (51.7% and 37.1% of capture, respectively). The same species prevailed in terrestrial and epiphytic bromeliads where scarce #T. infestans$ dark morph nymphal instars were also detected. In parrot nests #T. delpontei$ prevailed broadly over other species (90.2% of the capture) and only 4 #T. infestans$ dark morph adults were collected. In contrast, #T. infestans$ dark morph was the predominant species captured in hollow trees (46.0% of the total collected). The abundance of immature forms (88.2% of the collection) shows that hollow trees constitute a favourable ecotope for this species. Of the 421 trees investigated, 33.7% were positive for triatomines. #T. infestans$ dark morph, found inside 15.0% of them, also had higher apparent density than other species (average number of #T. infestans$ in positive trees, 2.0 plus or minus 1.6 vs 1.3 plus or minus 0.6 for other species). Light trapping seems to be an efficient method to sample the #T. sordida$-#T. guasayana$ complex in that it shows a similar distribution to that observed in natural ecotopes. However, this method is ineffective for the assessment of the local abundance of #T. infestans$ dark morph. (Résumé d'auteur)

International audience; DNA sequence comparison of 412 base-pairs fragments of the mitochondrial cytochrome B gene was used to infer the genetic structure of nine geographical #Triatoma infestans$ populations and their phylogenetic relationship with #T. melanosoma$ and #T. brasiliensis$. #T. infestans$ and #T. melanosoma$ were compared by morphometry, allozyme and cytogenetic analyses, as well as subjected to reciprocal crosses, in order to clarify the taxonomic status of the latter. No differences were found to distinguish the two species and the crosses between them yielded progeny. #T. infestans$ populations presented four haplotypes that could be separated in two clusters : one formed by the samples from Bolivia (Andes and Chaco) and the other formed by samples from Argentina and Brazil. Silvatic and domestic #T. infestans$ populations from Bolivia (Andes) were genetically identical. (Résumé d'auteur)

Clonal propagation of oil palm (Elaeis guineensis Jacq.) through somatic embryogenesis has been achieved by several research groups (Corley et al, 1977; Pannetier et al, 1981; Paranjothy, 1984), and its merits have been well discussed from a theoretical angle (Soh, 1986). The French ORSTOM-CIRAD group has developed a micropropagation process up to the pilot scale in four production units spread over three producing countries. In vitro vegetative propagation has led to the production of more than one million clonal plantlets to date. The technique has been proven by field performances on more than 2,500 ha of clonal plantations. Scaling-up of the current process has revealed several bottlenecks that are now limiting the commercial development of the tissue culture process. The main difficulties encountered at the pilot scale are: (i) the production costs and (ii) the occurrence of variant palms (ca. 5%) in embryogenically derived plant material. The production costs are still high because the process remains very labour- intensive and proliferation rates are overall rather slow. The development of oil palm embryogenic cell suspension has been achieved and will certainly enable the large-scale propagation of selected genotypes at low cost. Studies have been conducted in order to improve medium-term conservation of somatic embryos derived from embryogenic suspensions and the vigour of the regenerated plant material. This new process is currently assessed in terms of genetic fidelity.

One of the enduring problems in the epidemiology of sleeping sickness is that there are 3 morphologically indistinguishable subspecies of Trypanosoma brucei involved in a complex transmission cycle between humans, tsetse and reservoir hosts. Two subspecies, T. b. gambiense and T. b. rhodesiense, are infective to man and cause gambian and rhodesian sleeping sickness, respectively. The third subspecies T. b. brucei cannot by definition infect humans, but coexists with the other trypanosomes in reservoir hosts and vectors.

International audience; A genetic and morphologic survey of #Anopheles darlingi$ populations collected from seven countries in Central and South America was performed to clarify the taxonomic status of this major malaria vector species in the Americas. Population genetics was based on three techniques including isozyme, random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR), and internal transcribed spacer 2 (ITS2) markers. The results of the isozyme analysis indicated moderate differences in the allele frequencies of three putative loci (glutamate oxalaoacetate transaminase-1, isocitrate dehydrogenase-1, and phosphoglucomutase) of the 31 analyzed. No fixed electromorphic differences separated the populations of #An. darlingi$, which showed little genetic divergence (Nei distances = 0.976-0.995). Fragments produced by RAPD-PCR demonstrated evidence of geographic partitioning and showed that all populations were separated by small genetic distances as measured with the 1 - S distance matrix. The ITS2 sequences for all samples were identical except for four individuals from Belize that differed by a three-base deletion (CCC). The morphologic study demonstrated that the Euclidean distances ranged from 0.02 to 0.14, with the highest value observed between populations from Belize and Bolivia. Based on these analyses, all the #An. darlingi$ populations examined demonstrated a genetic similarity that is consistent with the existence of a single species and suggest that gene flow is occurring throughout the species' geographic range. (Résumé d'auteur)

La morphologie, les profils isoenzymatiques, la caryolgie, la gamme d'hôtes et l'analyse de l'ADN (PCR-RAPD) de quatre populations atypiques de #Meloidogyne javanica$ originaires du Brésil (P1-P4) ont été comparés à ceux de deux populations typiques appartenant à la même espèce (S1 et S2). Ces approches ont permis la séparation de ces populations en deux groupes : P1, S1 et S2, d'une part et P3 et P4, d'autre part. En se basant sur l'analyse de l'ADN, la population P2 présente une position intermédiaire, mais semble très proche de P1 d'après ses caractères morphologiques et le nombre de ses chromosomes. Elle en diffère cependant par son phénotype estérasique et par sa gamme d'hôtes. La technique de PCR-RAPD a permis la détection d'une variabilité intraspécifique notable. Cela représente un avantage certain par rapport à l'utilisation des isoenzymes et des gammes d'hôtes, dans la mesure où le nombre d'hôtes différentiels et de systèmes enzymatiques disponsibles est limité. Par comparaison avec d'autres études, nos résultats mettent en évidence une variabilité intraspécifique élevée chez #M. javanica$, espèce considérée jusque là comme relativement homogène. (Résumé d'auteur)

Cette communication montre une évaluation comparative des différentes techniques largement utilisées en génétique des populations. Dans un premier temps, nous dressons la liste des différents types de marqueurs en même temps que nous considérons leurs avantages et désavantages respectifs. Ensuite, nous présentons des exemples de leur utlisation à partir de nos travaux : polymorphisme de réaction antigène anticorps, allozymes, marqueurs nucléaires anonymes, polymorphisme d'amplification aléatoire, minisatellites, microsatellites, variation de l'ADN mitochondrial, RFLP, SSCP, séquençage. Le choix du marqueur dépendra de la question particulière à laquelle on veut répondre : hétérozygotie et sélection versus dérive génétique dans les populations naturelles, marqueurs génétiques pour les recherches en aquaculture. Des exemples de nos propres travaux qui illustrent ces points sont présentés. (Résumé d'auteur)

Une analyse RAPD a été réalisée à l'aide d'amorces arbitraires de 10 nucléotides, dans le but d'étudier la conformité génétique de régénérants de palmier à huile (#Elaeis guineensis$ Jacq) issus d'embryogenèse somatique. Des palmiers régénérants présentant le phénotype "mantled" ont été identifiés au champ, et la capacité des marqueurs RAPD à mettre en évidence ces variants a été vérifiée. Sur les 387 amorces testées, 259 (67%) ont permis d'amplifier avec succès les fragments d'ADN génomique de palmier à huile avec des profils électrophorétiques répétables. Sur ces 387 amorces, 73 (19%) ont permis d'identifier un polymorphisme entre clones. A partir de ces 73 amorces, 24 ont été sélectionnées pour une expérimentation à plus grande échelle, destinée à comparer, dans un premier temps le génome des têtes de clone avec celui des régénérants clonaux qui en étaient issus, puis, dans un deuxième temps les régénérants normaux et variants. En criblant les 8900 marqueurs générés, nous n'avons pas pu identifier de variabilité intraclonale ni de différences entre tête de clone et régénérants. Il apparaît donc que le protocole de micropropagation clonale employé pour le palmier à huile, basé sur l'embryogenèse somatique, n'induit pas d'importants bouleversements génomiques. Nos résultats ont permis de montrer que l'approche RAPD n'est pas appropriée à la détection du phénotype variant "mantled". Dans cet article, l'emploi des marqueurs RAPD pour la mise en évidence des variations somaclonales chez le palmier à huile est discutée, et des approches moléculaires alternatives sont proposées. (Résumé d'auteur)

Trypanosoma cruzi$, protozoaire parasite responsable de la maladie de Chagas en Amérique latine, est caractérisé par une très grande variabilité génétique. Les populations naturelles du parasite montrent une structure clonale typique, les échanges sexués entre clones étant très rares, même à l'échelle évolutive. Un échantillon de 100 souches de #T.cruzi$ représentatives de la diversité génétique globale du parasite, a été sélectionné et analysé par la technique du Polymorphisme Révélé par Amplification Aléatoire (Random Amplified Polymorphic DNA, RAPD). L'analyse phylogénétique des données a révélé la forte structuration de la diversité clonale en six clades nettement individualisés correspondant possiblement à des lignées clonales et regroupés en deux lignées phylogénétiques majeures. Des marqueurs RAPD spécifiques de clades ont été clonés et séquencés, ce qui a permis le développement de diagnostics PCR pour l'identification des lignées clonales. Les produits PCR varient en taille et en séquence, d'une lignée à l'autre, et correspondent aux multiples allèles d'un même gène, comme cela a été montré par analyse du polymorphisme de longueur des fragments de restriction (RFLP)et par séquençage. L'analyse généalogique d'un de ces gènes a révélé que certains allèles ont subi des transferts horizontaux entre lignées clonales, ce qui démontre que des événements de recombinaison génétique ont eu lieu, occasionnellement, au cours de l'histoire évolutive de #T. cruzi$. Les données fournies par le séquençage d'une portion de l'ADN mitochondrial correspondant au gène du cytochrome b sont en accord avec cette conclusion, et ont permis de déterminer les relations phylogéniques entre #T. cruzi$ et d'autres trypanosomes du sous-genre #Schizotrypanum$, parasites de nombreuses espèces de chauves-souris... (D'après résumé d'auteur)

RAPD markers were used to investigate the genetic diversity of 31 Brazilian cassava clones. The results were compared with the genetic diversity revealed by botanical descriptors. Both sets of variates revealed identical relationships among the cultivars. Multivariate analysis of genetic similarities placed genotypes destinated for consumption "in nature" in one group, and cultivars useful for flour production in another. Brazil's abundance of landraces presents a broad dispersion and is consequently an important resource of genetic variability. The botanical descriptors were not able to differentiate thirteen pairs of cultivars compared two-by-two, while only one was not differentiated by RAPD markers. These results showed the power of RAPD markers over botanical descriptors in studying genetic diversity, identifying duplicates, as well as validating, or improving a core collection. The latter is particularly important in this vegetatively propagated crop. (Résumé d'auteur)