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We examined the genotypic diversity of 64 Bradyrhizobium strains isolated from nodules from 27 native leguminous plant species in Senegal (West Africa) belonging to the genera Abrus , Alysicarpus , Bryaspis , Chamaecrista , Cassia , Crotalaria , Desmodium , Eriosema , Indigofera , Moghania , Rhynchosia , Sesbania , Tephrosia , and Zornia , which play an ecological role and have agronomic potential in arid regions. The strains were characterized by intergenic spacer (between 16S and 23S rRNA genes) PCR and restriction fragment length polymorphism (IGS PCR-RFLP) and amplified fragment length polymorphism (AFLP) fingerprinting analyses. Fifty-three reference strains of the different Bradyrhizobium species and described groups were included for comparison. The strains were diverse and formed 27 groups by AFLP and 16 groups by IGS PCR-RFLP. The sizes of the IGS PCR products from the Bradyrhizobium strains that were studied varied from 780 to 1,038 bp and were correlated with the IGS PCR-RFLP results. The grouping of strains was consistent by the three methods AFLP, IGS PCR-RFLP, and previously reported 16S amplified ribosomal DNA restriction analysis. For investigating the whole genome, AFLP was the most discriminative technique, thus being of particular interest for future taxonomic studies in Bradyrhizobium , for which DNA is difficult to obtain in quantity and quality to perform extensive DNA:DNA hybridizations.

An interspecific partial genetic linkage map of #Coffea$ sp. based on 62 backcross hybrids is presented. F1 hybrids were generated by a cross between the wild #C. pseudozanguebariae$ and the anciently cultivated #C. liberica$ var. #dewevrei$ (DEW) ; progeny were then derived from a backcross between F1 hybrid and DEW. The map construction consisted of a two-step strategy using 5.5 and 3.1 LOD scores revealed by simulation file. The map consisted of 181 loci : 167 amplified fragment length polymorphism (AFLP) and 13 radom fragment length polymorphism (RFLP) loci. The markers were assembled into 14 linkage groups, each with 4-31 markers covering 1,144 cM. Segregation distorsion was observed for 30% of all loci, in particular 3:1 and 1:3 ratios equally favouring each of the two parents. The existence of such ratios suggests genetic conversions events. This map also represents an initial step towards the detection of quantitative trait loci. (Résumé d'auteur)

The technique described here is a fast and simple method of extracting chloroplast DNA (cpDNA). It overcomes the need for differential centrifugation using density gradients. The leaves do not have to be kept in the dark and lyophilized before extraction, but lyophilization is still possible. The chloroplasts are specifically lysed in a cell extract of leaves, using a non-ionic detergent. After isolation by centrifugation, the cpDNA is purified by the combined action of proteolytic enzymes and detergents, followed by the elimination of proteins using a mixture of chloroform and isoamyl alcohol. This method provided good quality restriction profiles for all species analyzed.

At the present time, the precise taxonomial status of many strains classified as #Bradyrhizobium$ still remains unclear. There is a need to develop a reliable grouping method, specifying the genetic relationships between these strains. Phenotypic methods as auxanography or protein profiling did not prove valuable for classification of bradyrhizobia and were not in good agreement with phylogenetic data. The purpose of this work is to develop a strategy to analyse the diversity of bradyrhizobia and to identify genomic groups among our collection of strains isolated from 9 small legume species in Senegal. #B. japonicum$, #B. elkanii$ and representatives of previously described groups by Moreira et al. (1993) and Dupuy et al. (1994) were included as references. Bacterial diversity was assessed by two different techniques, PCR-RFLP analysis of the IGS region between 16S and 23S rDNA (IGS) and the AFLP technique. Groupings of strains obtained by the two methodologies will be presented and compared. 16S rDNA PCR-RFLP analysis of strains representative of IGS clusters from small legumes was also performed. (Résumé d'auteur)

Deux isolats de la granulose de #S. littoralis$ ont été isolés de larves mortes provenant de champs de cotton non traités dans les governorats Gharbeia et Sharkeia en Egypte. Les 2 isolats ont été caractérisés par leur profils de restriction. Les profils obtenus différent de celui publié précédement en provenance de Côte d'Ivoire en Afrique. Les profils polypeptidiques des capisdes ont été déterminé et comparé avec celui de leur homologue africain. Des tests biologiques ont été entrepris. (Résumé d'auteur)

We isolated 71 slow-growing bacterial strains from nodules of 27 native leguminous plants species in Senegal (West Africa) belonging to the genera #Abrus$, #Alysicarpus$, #Bryaspis$, #Chamaecrista$, #Cassia$, #Crotalaria$, #Desmodium$, #Eriosema$, #Indigofera$, #Moghania$, #Rhynchosia$, #Sesbania$, #Tephrosia$, and #Zornia$ playing an ecological role and having agronomic potential in arid regions. The isolates were charaterised by restriction fragment length polymorphism (RFLP) analysis of PCR-amplified 165 rDNA and comparative SDS-PAGE of whole-cell proteins ; reference strains of the different known rhizobial species and groups were included as references. We conclude that these nodule isolates are diverse, and form several phylogenetic subgroups inside #Bradyrhizobium$. Nodulation tests performed on 5 plant species demonstrated host specificity among the strains studied. (Résumé d'auteur)

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.

La NouvelleCalédonie possède une forte concentration en Casuarinaceae endémiques. On y dénombre huit espèces de #Gymnostoma# et une espèce de #Casuarina : C. collina#. Vingt-six souches de #Frankia# ont été isolées de nodules de #C. collina# et étudiées par diverses techniques incluant l'infectivité, l'effectivité, le spectre d'hôte et la PCR/RFLP de l'ITS 16S-23S. Tous ces #Frankia# présentent les mêmes caractéristiques que celles décrites chez les souches atypiques de #Casuarina# spp. Ce travail a mis en évidence, chez les #Frankia# de #C. collina#, les caractéristiques originales suivantes : (i) ils sont localisés à l'intérieur des nodules ; (ii) ils appartiennent au groupe des #Frankia# infectifs sur #Elaeagnus#;(iii) ils se regroupent dans quatre groupes ITS déjà décrits chez #Gymnostoma#. En fait, il est très probable que les souches atypiques de #C. collina# et les #Frankia# de #Gymnostoma# soient les mêmes. On peut formuler l'hypothèse que les #Frankia# de #Gymnostoma# pourraient utiliser #C. collina# comme alternative en absence de leur hôte naturel ou quand les conditions écologiques sont favorables à #C. collina#.

Analyses of DNA polymorphism and virulence variation were used to evaluate the population structure of Xanthomonas axonopodis pv. manihotis, the pathogen causing cassava bacterial blight in Colombia. We collected strains from the major cassava-growing regions which can be grouped into different edaphoclimatic zones (ECZs) according to environmental conditions, production constraints, and economic parameters. DNA polymorphism was assessed by a restriction fragment length polymorphism analysis, using an X. axonopodis pv. manihotis plasmid DNA sequence (pthB) as a probe to evaluate the genetic relatedness among 189 Colombian strains. The sampling intensity permitted the estimation of genetic differentiation within and among ECZs, sites, and fields and even within an individual plant. A multiple correspondence analysis indicated that the Colombian X. axonopodis pv. manihotis population showed a high degree of diversity relative to X. axonopodis pv. manihotis populations studied previously, and the entire collection was grouped into seven clusters. A general correlation was observed between the clusters and the geographical origin of the strains, as each cluster was largely composed of strains from the same ECZ. Representative strains, identified with pthB, were further characterized by ribotyping, hybridization to two repetitive genomic probes (pBS6 and pBS8), and restriction analysis of plasmid contents to evaluate the complementarity of these markers. Virulence variation was observed within the Colombian collection. Strains of different aggressiveness were found in all ecological zones, but no correlation between virulence variation and DNA polymorphism was observed. The genetic and virulence analyses contribute to understanding the X. axonopodis pv. manihotis population structure in Colombia.

RFLP analysis of mitochondrial DNA (mtDNA) was used to study variation within 13 populations of #Clarias batrachus$, sampled respectively in Vietnam, Thailand and in the Indonesian Archipelago. In this study an amplified region corresponding approximately to 2.3 kilobases of the Cytochrome-b and D-loop genes was digested using 8 restriction enzymes (HinfI, Hin6I, MvaI, MspI, HaeIII, BanHI, NdeII, DraI). 12 mtDNA haplotypes were found in 40 specimens. Each sampling location was characterised by one haplotype, except Palembang (Sumatra, Indonesia) and Samarinda (Kalimantan, Indonesia) where 2 and 4 haplotypes were found respectively. The consensus tree calculated from 15 more parsimonious networks showed that mtDNA haplotypes are geographically distributed. Three well differentiated clusters were identified. The first cluster is composed by populations from both Thailand and Vietnam, the second cluster by two populations from West Sumatra between populations which come from highlands (altiude more than 1000 meters in Bukittingui, and 300 meters in Nias Island) and populations located in lowlands. The significant genetic relatedness observed between populations from Sumatra (Jambi, Palembang, Muara Tebo, Teluk Kuantan) and populations from Java indicate a possible common origin which is probably in Kalimantan. This result is supported by the high diversity of haplotypes revealed in Samarinda (Kalimantan) and their intermediate position in the genetic network. The populations from highlands in West Sumatra which share a common haplotype are genetically more related to populations from Thailand and Vietnam than to populations from the rest of Indonesia. These populations seems to be relict populations from a first colonisation event which arise from the continental part of Asia... (D'après résumé d'auteur)

La réaction en chaîne des polymérases/polymorphisme des fragments de restriction (PCR-RFLP) a été utilisée pour séparer des isolats du nématode #Bursaphelenchus$. Les isolats de #B. xylophilus$ examinés provenaient du Japon, des USA, de Chine et du Canada, et ceux de #B. mucronatus$ du Japon, de Chine et de la France. L'ADN ribosomal contenant le gène 5.8S, les segments de transciption interne 1 et 2, et les segments partiels des gènes 18S et 28S ont été amplifiés par PCR. La digestion des produits amplifiés provenant de chaque isolat à l'aide de douze endonucléases de restriction et l'examen des données en RFLP qui en découlent révèlent, par une analyse en grappe, une séparation significative entre #B. xylophilus$ et #B. mucronatus$. Parmi les isolats de #B. xylophilus$ examinés, les isolats pathogènes du Japon, ceux de Chine et des USA étaient tous identiques, tandis que les isloats non pathogènes du Japon étaient légèrement distincts et que ceux du Canada formaient une grappe séparée. Parmi les isolats de #B. mucronatus$, deux isolats provenant du Japon étaient très semblables ; de même un autre isolat du Japon et un isolat de Chine étaient identiques. Les données provenant des séquences d'ADN montrent 98 différences (substitution nucléotidiques ou séparations) dans les 884 paires de bases examinées chez les isolats de #B. xylophilus$ et #B. mucronatus$. Les données provenant des séquences d'ADN chez #Aphelenchus avenae$ et #Aphelenchoides fragariae$ diffèrent non seulement de celles des #Bursaphelenchus$ mais aussi entre elles. Afin de préciser les relations phylogéniques de ces espèces, les données séquentielles du gène 5.8S provenant de l'ADN ribosomal ont été examinées... (D'après résume d'auteur)

Resistance to antifolate antimalarial drugs (cycloguanil, a biologically active metabolite of proguanil, and pyrimethamine) is associated with a Ser- to Asn-108 point mutation in the dihydrofolate reductase thymidylate synthase gene of #Plasmodium falciparum$. The frequency of this mutation was studied in 127 clinical isolates obtained in Yaounde, Cameroon using a simple and rapid molecular technique based on the polymerase chain reaction and restriction fragment lengh polymorphism. Of the 127 isolates, pure wild-type Ser-108 codon, pure mutant-type Asn-108 codon, and mixed codons were observed in 66, 55, and six parasites, respectively. The proportion of antifolate-resistant, pure mutant-type codon, with respect to pure wild-type or mixed alleles, was 43% (55 to 127). The results of the molecular assay were compared with those of semimicro isotopic in vitro assay in 34 isolates. All 17 pure Ser-108 isolates and two isolates with mixed alleles were sensitive to both pyrimethamine (50% inhibitory concentration [IC50] < 100 nM) and cycloguanil (IC50 < 50 nM). Fourteen of 15 isolates with the mutant-type Asn-108 codon were resistant to pyrimethamine and cycloguanil. One isolate with Asn-108 showed a slightly elevated pyrimethamine IC50 (78 nM), which was within the sensitive range. This study provides further evidence that antifolate-resistant #P. falciparum$ isolates are already present in Yaounde, Cameroon. (Résumé d'auteur)

DNA polymorphism and variation in virulence of #Xanthomonas axonopodis$ pv. #manihotis$ (Xam), the causal agent of cassava bacterial blight, were studied within a pathogen population from Venezuela. Collections were made in several fields at different sites within an edaphoclimatic zone where cassava is a major crop. DNA polymorphism was assessed by RFLP analysis, using an Xam plasmidic DNA sequence (ptbB) as a probe to determine the relatedness of 91 Venezuelan isolates. A high degree of polymorphism existed among the isolates, whether collected from the same or different fields. Based on a multiple correspondence analysis, the Xam population was distributed into eight clusters and no correlation was observed between genetic diversity and geographic origin. One set of haplotype strains representing the range of variability detected in Venezuela was further characterized by another RFLP analysis using two repetitive genomic probes (pBS6 and pBS8) to establish the usefulness of these probes and their complementarity with the ptbB probe. Variation for virulence was observed in the Xam Venezuelan collection by inoculating a set of cassava cultivars with 28 isolates of the pathogen, each representig a haplotype. Understanding the genetic and pathogenic variation in the pathogen population is useful for designing cassava bacterial blight management strategies. (Résumé d'auteur)

Strains of #Xanthomonas campestris$ pv. #vignicola$ (Xcv), isolated from cowpea leaves with blight or minute pustules and collected from various geographic areas, were selected on the basis of pathological and physiological features. All strains were analyzed for genotypic markers by two methods : ribotyping with EcoRI endonuclease, and RFLP analysis with a plasmid probe (pthB) containing a gene required for pathogenicity from #Xanthomonas campestris$ pv. #manihotis$. Ribotyping revealed a unique pattern for all the strains that corresponded to the previously described ribotype rRNA7. Based on polymorphism detected by pthB among Xcv strains, nine haplotypes were defined. The observed genetic variation was independent of the geographic origin of the strains and of pathogenic variation. Some haplotypes were widely distributed, whereas others were localized. In some cases, we could differentiate strains isolated from blight symptoms and pustules according to haplotypic composition. However, in most cases, no significant differences were observed. Our results and the previous pathogenic and biochemical characterizations suggest that the strains isolated from leaves with blight symptoms or minute pustules belong to the same pathovar. We provide information on pathogen diversity that can be used to identify and characterize resistant germplasm. (Résumé d'auteur)

L'analyse du polymorphisme de longueur des fragments de restriction d'ADN amplifie (PCR-RFLP) presente de nombreux avantages pour la caracterisation de la diversite microbienne: relative rapidite, faible cout, possibilite d'application a l'ensemlble ries taxons bacteriens, bonne reproductibilite, possibilite d'analyse simultanee d'un grand nombre de souches, interet au niveau taxonomique. Afin d'optimiser sort usage, nous avons cherche a determiner combien d'enzymes et lesquels etaient le plus approprie, en effectuant une analyse systematique par ordinateur de la capacite de 25 enzymes de restriction differentes a generer par PCR-RFLP, seules ou en combinaison, (les profils de digestion permettant la distinction d'especes proches taxonomiquement. La sous-unite 16S de l'ARN ribosomal (rrs; pour ribosomal RNA small subunit) a ete choisie pour simuler ces PCR-RFLP: elle correspond a la region la plus frequemment etudiee et permet en general une bonne discrimination au niveau de l'espece; de plus, de nombreuses sequences rrs sont disponibles dans les banques de donnees. L'etude a ete focalisee sur les rhizobia qui representent un bon modele de genres differents, entremeles avec d'autres genres tres proches taxonomiquement, et parce que leur importance en agriculture induit la necessite d'outils performants pour la caracterisation de grands nombres de nouveaux isolats. La digestion de 24 sequences rrs correspondant aux souches-types de differentes especes a ete simulee par ordinateur. Les profils de digestion obtenus pour les differentes sequences ont ete compares deux par deux afin de determiner le nombre de profils distincts generes par chaque enzyme individuellement. ou par les combinaisons systematiques de 2, 3, 4, 5, 6 ou 7 enzymes. Differentes combinaisons de 3, 4 ou 5 enzymes permettent la distinction entre les especes. La frequence a laquelle les differentes enzymes sont trouvees dans les i:ounfiinaisons discrimimantes ne correspond pas completement a leur pouvoir de discrimation individuel, mais a la complementarite qu'elles presentent lorsqu'ellas sont analysees ensemble. La combination des profils obtenus avec six enzymes, choisies parmi les sept puis frequentes dans les combinaisons discriminantes, permet en moyenne de distinguer plus de 99,5%, des sequences etudiees, quelle que soit la similarite entre ces sequences. L'utilisation d'au moins six de ces sept enzymes est suggeree afin d'assurer une bonne distinction des especes de rhizobia, connues et inconnues.

The biodiversity of nitrogen-fixing organisms is huge. Taxonomic and phylogenetic research is needed to structure this diversity, to facilitate communication among scientists, and to increase our understanding of the evolution and biology of diazotrophs. Molecular tools for taxonomic and biodiversity studies of diazotrophic rhizobia, frankiae, cyanobacteria and bacilli are presented in sections 2 to 5. Sections 6 to 9 focus on problems with genus and species assignment.

Neptunia oleracea is an annual aquatic stem-nodulated legume indigeneous of waterlogged places in Senegal. Bacterial isolates from nodules of N. oleracea can infect Medicago sativa roots but the nodules are not efficient. No information is available on the taxonomy of Neptunia specific bacteria.

Une enquête a été menée concernant les nématodes entomopathogènes dans les cinq régions climatiques du Japon : les îles subtropicales, la région tempérée chaude des côtes du pacifique, la région montagneuse australe, la région tempérée et la région tempérée froide. Plus de 1400 échantillons de sol provenant de 266 sites ont été testés pour la présence de nématodes à l'aide de #Galleria$-pièges. Cent vingt-et-un Steinernematides et 29 Heterorhabditides ont été détectés dans, respectivement, 62 et 64 sites. Huit espèces de Steinernematides ont été reconnues : sept espèces non décrites et #Steinernema kushidai$. Chacune des espèces montre une répartition particulière : trois sont très répandues, une est côtière, une subtropicale et les trois autres montagnardes. En contraste, les #Heterorhabditidae$ ont été identifiés comme #Heterorhabiditis indica$ et #H. megidis$. La première espèce est largement répandue dans la région côtière depuis la zone subtropicale jusqu'à la zone tempérée chaude, tandis que la seconde est surtout rencontrée dans la partie est de la région côtière tempérée. (Résumé d'auteur)

It has been postulated that chloroquine resistance may be associated with a single point mutation at codon 86 of the #Plasmodium falciparum$ multidrug resistance 1 (pfmdr 1) gene. Using a simple and rapid molecular technique involving polymerase chain reaction and restriction fragment length polymorphism, the frequency of the Asn-to-Tyr mutation associated with chloroquine resistance was established among 129 clinical isolates obtained from indigenous patients in Yaoundé, Cameroon. The results showed that 110 of 129 isolates display a mutant codon. The other clinical isolates had either a pure wild-type Asn-86 codon (n = 12) or mixed Asn/Tyr alleles (n = 7). In vitro drug assays were performed to compare the genotype and phenotype in 102 clinical isolates. Of these isolates, 86 displayed pure Tyr-86 mutant codon ; 48 (56%) mutant isolates were chloroquine-resistant (50% inhibitory concentration [IC50] > 100 nM), as expected, but 38 (44%) mutant isolates were chloroquine-sensitive (IC50 < 100 nM). Three chloroquine-resistant isolates and seven chloroquine-sensitive parasites carried a wild-type Asn-86 codon. Mixed alleles were found in six isolates (four chloroquine-sensitive and two chloroquine-resistant isolates). Our results did not confirm previous observations on the possible association between chloroquine resistance phenotype and genotype based on the pfmdr 1 gene. (Résumé d'auteur)

Afin d'étudier les possibilités offertes par l'hybridation interspécifique chez #Coffea canephora$, un croisement modèle entre deux espèces phylogénétiquement éloignées est étudié : #C. canephora$ (PSE) x #C. liberica$ var. #dewevrei$ (DEW), proche de #C. canephora$. La quantité d'ADN nucléaire des deux espèces est respectivement de 1,13 pg et de 1,43 pg. Elle peut s'expliquer par des différences de constitution chromosomique principalement au sein de séquences non codantes, essentiellement répétées. La construction d'une banque a été préférée à des méthodes plus sélectives de façon à couvrir le génome en entier. A partir d'une banque d'ADN génomique d'hybride F1 restreint aux site GATC, par l'endonucléase Sau3A, 193 clones contenant des séquences répétées ont été retenus, après rétrohybridation. Vingt deux sondes sont totalement séquencées, 5 partiellement. Elles sont riches en AT et montrent souvent des sites GATC internes. La plupart ne présente pas d'homologie avec les séquences connues. Trois sondes sont analysées de façon plus approfondie sur les espèces parentes PSE et DEW et sur 8 autres espèces choisies pour leur origine géographique et leur quantité d'ADN (#C. racemosa$, #C. sessiliflora$, #C. eugenioides$, #C. sp$ "#Moloundou$", #C. canephora$, #C. congensis$ et #C. heterocalyx$). La première est constituée de quatre séquences distinctes, dont une au moins répétée en tandem. La seconde révèle une forte homologie avec des séquences codant pour la reverse-transcriptase de rétrotransposon de type gypsy-like, tant au niveau nucléotidique qu'au niveau acides aminés. Elle est donc, le premier rétrotransposon découvert chez les caféiers. La dernière possède des profils RFLP sur l'ADN différents uniquement pour les deux espèces à forte quantité d'ADN. Il est primordial de poursuivre l'étude du rétrotransposon pour préciser son nombre de répétitions, sa structure fine et sa capacité à transposer... (D'après résumé d'auteur)

We analysed the genetic differentiation among 17 natural populations of the Nile tilapia Oreochromis niloticus (Linnaeus, 1758) using allozymes and restriction fragment length polymorphism (RFLP) of mitochondrial DNA (mtDNA). The populations studied, from the River Senegal to Lake Tana and from Lake Manzalla to Lake Baringo, represent all subspecies which have been previously described. Sixteen variable nuclear loci showed that these populations can be clustered in three groups: (1) West African populations (Senegal, Niger, Volta and Chad drainages), (2) Ethiopian Rift Valley populations (Lakes Awasa, Ziway, Koka and the Awash River) and (3) Nile drainage (Manzalla, Cairo, Lake Edward) and Kenyan Rift Valley populations (Lakes Turkana, Baringo and River Suguta). Nine different mtDNA haplotypes were found in the RFLP analysis of a 1 kb portion of the D-loop region. The network obtained showed that there are three geographically distinct groups; all West African populations and O. aureus are clustered, the two Ethiopian Rift Valley populations are distinct and between these two groups are the Kenyan and Ugandan Rift Valley populations. Nile populations show affinities both with West African populations and with specimens from Lakes Tana and Turkana. Taxonomic and biogeographical implications of these results are discussed.

Two doubled-haploid rice populations, IR64/Azucena and IRAT177/Apura, were used to identify markers linked to rice yellow mottle virus (RYMV) resistance using core restriction fragment length polymorphism (RFLP) maps. Resistance was measured by mechanical inoculation of 19-day-old seedlings followed by assessment of virus content by enzyme-linked immunosorbent assay tests 15 days after inoculation. IR64/Azucena and IRAT177/Apura populations, 72 and 43 lines, respectively, were evaluated, and resistance was found to be polygenic. Resistance was expressed as a slower virus multiplication, low symptom expression, and limited yield loss when assessed at the field level. Bulked segregant analysis using the IR64/Azucena population identified a single random amplified polymorphic DNA marker that mapped on chromosome 12 and corresponded to a major quantitative trait locus (QTL) evidenced by interval mapping. When pooling RFLP data, integrated mapping of this chromosome revealed that the QTL was common to the two populations and corresponded to a small chromosomal segment known to contain a cluster of major blast resistance genes. This region of the genome also reflected the differentiation observed at the RFLP level between the subspecies #indica$ and #japonica$ of #Oryza sativa$. This is consistent with the observation that most sources of RYMV resistance used in rice breeding are found in upland rice varieties that typically belong to the #japonica$ subspecies. (Résumé d'auteur)

A sample of African #Clarias$ catfishes from the Senegal River was studied using morphometry, allozyme variation, microsatellites and RFLPs of mitochondrial DNA. They all confirmed the presence of two species, #C. gariepinus$ and #C. anguillaris$. The two species were closely related genetically and no diagnostic loci were found in allozymes and microsatellites studies. Two of the 11 haplotypes of mtDNA observed were shared by both species. Three of the four assays (morphometry, allozymes and microsatellites) allowed a precise characterization of both. One specimen occupied an intermediate position in the analysis of the data ; it was considered an F1 hybrid whose possible origin is discussed. (Résumé d'auteur)

From 1989 to 1992, a longitudinal study of the relationships between different tick species and domestic ungulates in the transmission and amplification of Crimean-Congo hemorrhagic fever (CCHF) virus was undertaken in the Bandia area in Senegal where the presence of the virus had been reported previously. An epizootic occurred in 1991-1992 and 22 strains of CCHF virus were isolated from Hyalomma marginatum rufipes Koch, Amblyomma variegatum (F.), Rhipicephalus guilhoni Morel & Vassiliades, and R. evertsi evertsi Neumann ticks collected from cattle and goats. No human cases were reported. Transmission of CCHF virus in the area involves a complicated pattern including many tick species and hosts. Amplicons of the S fragment (536 bp) of the CCHF genome of 12 isolates from the study were obtained by polymerase chain reaction and analyzed by restriction-length fragment polymorphism. Three different genotypes of CCHF virus were identified and present during the epizootic. One genotype was recovered from A. variegatum, R. guilhoni, and R. e. evertsi and 2 genotypes were isolated from H. m. rufipes.

*INRA, Unite Centrale de Documentation, Jouy-en-Josas (FRA) Diffusion du document : INRA, Unite Centrale de Documentation, Jouy-en-Josas (FRA) Diplôme : BTS

Cultivated varieties of rice are the result of several thousands of years of human selection from the available genetic diversity, in various natural environments and human cultures. The process of gathering varieties from different geographic origins, planting them in the same field, and selecting particular genotypes among the offsprings of natural hybridization can still be observed in traditional societies and has no doubt been going on since early days. Modern breeding in the last century has done little more than to control the process of hybridization and selection in a more efficient way, and the result has been to adapt varieties to better controlled and fertilized environments. The basic approach consists of choosing parents with complementary characters in order to combine them. Unexpected (transgressive) characters are also obtained in the process. Evaluation of germplasm is generally a matter of screening for useful characters although the understanding of the genetic structure of genetic resources can give a clue to obtain transgressive characters (Second and Charrier 1989).

Plasmids were recovered by an alkaline procedure from six symbiotically effective strains of Rhizobium meliloti of diverse geographical origin, reported to harbour only one middle-size large plasmid (ranging from 89 to 143 Megadaltons). Each purified plasmid was digested with eight restriction endonucleases; cleavage patterns were very complex: only KpnI and XbaI gave a limited number of bands. Fingerprints were very different, whatever the restriction enzyme or the geographical origin of the strains. However, Southern DNA-DNA hybridizations revealed that the plasmids showed homologous sequences having a high thermal stability. We gave evidence that some of these sequences are common to all the plasmids of R. meliloti. The biological function of these common sequences is unknown. Hybridization with cloned nitrogen fixation (nif) genes from Klebsiella pneumoniae had demonstrated that nif genes were not located on the middle -- size plasmids of R. meliloti studied in this paper.

The taxonomy of the #Culex pipiens$ complex remains a controversial issue in mosquito systematics. Based on morphologic characters, 2 allopatric taxa are recognized, namely #Cx. pipiens$ (including the form "#molestus$") in temperate areas and #Cx. quinquefasciatus$ in tropical areas. Here we report on variability at nucleotide level of an acetylcholinesterase gene in several strains and natural populations of this species complex. Few polymorphisms were found in coding regions within a subspecies but many polymorphisms were observed between subspecies in noncoding regions. We describe a method based on a restriction enzyme polymorphism in polmerase chain reaction-amplified DNA, in which the presence or absence of one restriction site discriminates #Cx. pipiens$, #Cx. quinquefasciatus$, and their hybrids. This technique reliably discriminates mosquitoes from more than 30 worldwide strains or populations. Polymerase chain reaction amplification of specific alleles may also be a useful tool for characterizing specific alleles of each sibling taxon. (Résumé d'auteur)

Fifty-one fast growing rhizobial strains isolated from root nodules of #Acacia senegal$ and #Prosopis chilensis$ in Sudan and Kenya were divided into DNA homology groups using non-radioactive DNA-DNA dot-blot hybridisation. #Rhizobium leguminosarum$ , #R. galegae$, #R. tropici$, #Mesorhizobium loti$, #Sinorhizobium fredii$, #S. meliloti$ used in numerical taxonomy were included in the hybridisation experiments as reference strains and, at a later strage #S. saheli$ and #S. terangae$. Scores given to the intensities of dots detected in the hybridisation experiments were used in principal component analysis, which clustered the majority of the tree rhizobia in two separate DNA-homology groups. The 51 strains were also analysed by genomic fingerprinting using the repetitive sequence-based polymerase chain reaction (rep-PCR) method with REP, ERIC, BOX and GTG5 primers. The resulting genomic fingerprints were compared with strains representing 15 rhizobial species. The relationship of 17 Sudanese strains to established sinorhizobial species was examined using the optical renaturation rates method and the G+C content of nine strains was determined. Results from dot-blot hybridisation and rep-PCR experiments were found to be in close agreement with each other and with the results obtained from spectrophotometric reassociation analysis. We suggest that rep-PCR fingerprinting can be used as a first and dot-blot hybridisation as a second rapid and dependable genomic screening method to classify new rhizobial isolates of unknown taxonomic status and to choose the representative strains for the more laborious DNA-DNA reassociation experiments. (Résumé d'auteur)

We obtained nine bacterial isolates from root or collar nodules of the non-stem-nodulated #Aeschynomene$ species #A. elaphroxylon$, #A. uniflora$, or #A. schimperi$ and 69 root or stem nodule isolates from the stem-nodulated #Aeschynomene$ species #A. afraspera$, #A. ciliata$, #A. indica$, #A. nilotica$, #A. sensitiva$, and #A. tambacoundensis$ from various places in Senegal. These isolates, together with 45 previous isolates from various #Aeschynomene$ species, were studied for host-specific nodulation within the genus #Aeschynomene$, also revisiting cross-inoculation groups described previously by D. Alazard (Appl. Environ. Microbiol. 50:732-734, 1985). The whole collection of #Aeschynomene$ nodule isolates was screened for synthesis of photosynthetic pigments by spectrometry, high pressure liquid chromatography, and thin layer chromatography analyses. The presence of puf genes in photosynthetic #Aeschynomene$ isolates was evidenced both by Southern hybridization with a #Rhodobacter capsulatus$ photosynthetic gene probe and by DNA amplificaton with primers defined from photosynthetic genes. In addition, amplified 16S ribosomal DNA restriction analysis was performed on 45 #Aeschynomene$ isolates, including strain BTAi1, and 19 reference strains from #Bradyrhizobium japonicum$, #Bradyrhizobium elkani$, and other #Bradyrhizobium$ sp. strains of uncertain taxonomic positions. The 16S rRNA gene sequence of the photosynthetic strain ORS278 (LMG 12187) was determined and compared to sequences from databases. Our main conclusion is that photosynthetic #Aeschynomene$ nodule isolates share the ability to nodulate particular stem-modulated species and form a separate subbranch on the #Bradyrhizobium$ rRNA, distinct from #B. japonicum$ and #B. elkanii$. (Résumé d'auteur)

The African Anopheles funestus and the Asian An. minimus groups are closely related and are probably considered distinct only because of their geographic separation. This study aimed at improving two identification methods based on polymerase chain reactionrestriction fragment length polymorphism (PCR-RFLP) already devel- oped for either group. Each PCR-RFLP, either on the internal transcribed spacer 2 (ITS2) for the An. minimus group, and domain 3 (D3) for the An. funestus group, was applied to the other group for the standardization of one identifi- cation method applicable on both continents. The ITS2 fragment digested by Bsi ZI showed the highest diagnostic power. This assay allowed the discrimination of at least 13 Anopheles species within the subgenus Cellia from two continents (Africa and Asia), among which are five major malaria vectors. Moreover, digestion of the D3 with Msp I showed intragenomic variations within An. funestus populations. Two types of D3 copies (M and W) occurred in specimens from southern Africa. The populations from West-Central Africa presented only type W and East-Malagasy populations exhibited type M. Since An. funestus shows a great capacity of adaptation, these molecular variations, along with behavioral and ecologic ones, reinforce the hypothesis of a species complex that will need to be further investigated.