Traditional evolutionary models depict evolution as a bifurcating pattern with a single ancestor diverging to form two lineages. However, reticulate species resulting from hybridization and recombination have unique histories shared with two independent lineages, not one. Accounting for the genetic histories of reticulate species increases the power and ability to recover biologically meaningful relationships. The genus Collomia (Polemoniaceae) is used to explore issues of reticulation and the importance of accounting for gene histories in a phylogenetic analysis. The issue of reticulation within species trees is discussed with a multilabeled, network approach being explored to better represent the genus's evolutionary history. Wherry's hypotheses regarding the relationships that exist within Collomia are addressed and the need for a new intrageneric section is recognized based on support from multiple, independent genes and morphology. Sections Collomiastrum and Courtoisia remain as previously circumscribed. Section Collomia is modified with removal of two species, C. grandiflora and C. biflora from the section and by erecting a new section, Calyperona. A morphological key is included for each section and their corresponding species, followed by sectional discussions. Finally, the evolution of lifecycle duration, seed morphology, and pollen morphology are discussed based on the phylogeny of the genus.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24826号 / 理博第4975号 / 新制||理||1710(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)准教授 中野, 智之, 教授 朝倉, 彰, 教授 森, 哲 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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Among viral diseases affecting cultivated tomato, Tomato yellow leaf curl disease (TYLCD) is one of the most devastating. This disease is caused by a complex of viruses of which Tomato yellow leaf curl virus (TYLCV) is regarded as the most important species. Current control strategies to fight viral diseases in tomato are mainly based on genetic resistance derived from wild relatives. In the present thesis, resistance derived from S. chilense and S. peruvianum has been exploited in breeding for resistance to TYLCD. In a previous study, TYLCV-resistant breeding lines derived from LA1932, LA1960 and LA1971 S. chilense accessions were developed. Therefore, the first objective of this thesis was to study the genetic control of the resistance derived from these accessions. With this aim, response to viral infection was assayed in segregating generations derived from the aforementioned resistant lines. The results obtained were compatible with a monogenic control of resistance. Resistance levels were higher in LA1960- and LA1971-derived F2 generations, as shown by slighter symptoms in the resistant plants and a higher number of asymptomatic plants compared with the results obtained in the LA1932-derived F2 generation. It is noteworthy that the level of resistance present in our materials is comparable to or even higher than the levels found in tomato lines homozygous for Ty-1. The response in plants heterozygous for the resistance gene was comparable to the response in homozygous plants for all three sources employed. This implies that the resistance genes derived from all three sources seem to be almost completely dominant. This effect was stronger for LA1971-derived resistance. The results were similar when comparing viral accumulation, as was expected, since a positive correlation was found in these families between viral accumulation and symptom scores. This has important implications in breeding, since the resistance will be used mostly for hybrid development. Our second objective was to map the loci associated with the major resistance genes identified. A total of 263 markers were screened, 94 of them being polymorphic between both species. Recombinant analysis allowed the resistance loci to be localized on chromosome 6, in a marker interval of 25 cM. This interval includes the Ty-1/Ty-3 region, where two S. chilense-derived TYLCD resistance loci were previously mapped. In order to test if the resistance genes identified in our populations were allelic to Ty-1 and Ty-3, further fine mapping was carried out. A total of 13 additional molecular markers distributed on chromosome 6 allowed 66 recombinants to be identified, and the resistance region to be shortened to a marker interval of approximately 950 kb, which overlaps with the Ty-1/Ty-3 region described previously by other authors. Therefore, the results obtained indicate that closely linked genes or alleles of the same gene govern TYLCV resistance in several S. chilense accessions. The third objective of the present thesis was to start the construction of a set of introgression lines (ILs) derived from Solanum peruvianum accession PI 126944 into the cultivated tomato genetic background. Once this collection of ILs is developed, it will represent a powerful tool for exploiting the resistance to different pathogens found in this particular accession in addition to other possible characters of interest. The starting plant material consisted of several segregating generations that were derived from two interspecific hybrids previously obtained by our group. Many crosses and embryo rescue were required to obtain subsequent generations due to the high sexual incompatibility that exists between tomato and PI 126944. Several mature fruits from the most advanced generations produced a few viable seeds, although embryo rescue was also employed to obtain progeny. As only a few plants were obtained by direct backcrossing, additional crosses were made in order to increase the number of descendants. A high degree of incompatibility was also found in crosses between sib plants. A total of 263 molecular markers were tested in some generations, 105 being polymorphic between tomato and PI 126944. Available generations were genotyped with these polymorphic markers in order to determine which alleles of S. peruvianum were already introgressed. On average, 79, 78 and 84 % of the S. peruvianum genome was represented in the pseudo-F2, pseudo-F4 and pseudo-F5 generations, respectively, for the markers analyzed. A reduction in the S. peruvianum genome was observed in more advanced generations, such as BC1 (56 %), pseudo-F2-BC1 (60 %) and pseudo-F3-BC1 (70 %). A greater reduction was observed in the pseudo-F3-BC2 generation (33 %). As a consequence of the reduction in the S. peruvianum genome, a loss of incompatibility was observed in some cases. The S. peruvianum genome was almost completely represented among the different plants of the most advanced generations. An evaluation for resistance to TYLCD and Tomato spotted wilt virus (TSWV) was carried out in some of the advanced generations, some of which were resistant to one or both viruses. In conclusion, we have conducted a successful and deeper exploitation of two wild species with proved resistance to TYLCD, S. chilense and S. peruvianum, identifying and fine mapping new genes of resistance. / Julián Rodríguez, O. (2014). Exploitation of Solanum chilense and Solanum peruvianum in tomato breeding for resistance to Tomato yellow leaf curl disease [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/36867

Tesis por compendio / La entrada PI 126944 de S. peruvianum ha sido descrita como resistente a distintos estreses bióticos, entre ellos a la enfermedad del rizado amarillo del tomate (Tomato yellow leaf curl disease, TYLCD). En trabajos previos realizados en el Instituto Universitario para la Conservación y Mejora de la Agrodiversidad Valenciana (COMAV) se obtuvieron tres híbridos interespecíficos entre esta entrada y el tomate cultivado, empleando el rescate de semillas inmaduras. En trabajos posteriores se desarrollaron generaciones más avanzadas a partir de estos materiales, incluyendo hasta las generaciones pseudo-F6 y retrocruces hacia la especie cultivada de algunas de las generaciones pseudo-Fn. Con objeto de aprovechar estos materiales en la mejora del tomate cultivado se inició, en trabajos anteriores del grupo, el desarrollo de un conjunto de líneas de introgresión (Introgression lines, ILs) que contengan el genoma de la entrada PI 126944 en el fondo genético de S. lycopersicum. Para tener correctamente representado el genoma de la especie donante en el fondo genético del tomate es necesario obtener un gran número de descendientes, por lo que es necesario optimizar los protocolos. El primer objetivo de esta tesis fue el estudio de distintos factores implicados en la superación de las barreras de incompatibilidad, con objeto de conseguir un elevado número de descendientes y maximizar la probabilidad de introgresar el genoma de PI 126944 en el conjunto de ILs. Se llevaron a cabo tres ensayos de retrocruce, iniciados con diferentes plantas de las generaciones pseudo-F4, pseudo-F5 y pseudo-F6. El genotipo de los parentales resultó ser un factor determinante en la obtención de descendencia, por lo que se recomienda utilizar el máximo número de genotipos distintos, con objeto de maximizar la probabilidad de obtener progenie. Se llevó a cabo una prueba de medios de cultivo que permitió seleccionar la combinación más adecuada de auxinas y citoquininas para el cultivo de semillas inmaduras y posterior regeneración de plantas. También se estudió el efecto del número de días transcurridos desde la polinización hasta la recolección de los frutos. Tal y como se ha comentado anteriormente, esta colección del ILs presenta interés por la resistencia del parental donante a TYLCD. Una vez se complete la colección, se evaluará por su resistencia a esta enfermedad. Los estudios previos han mostrado que se trata probablemente de una resistencia poligénica, cuya expresión a menudo es más dependiente de las condiciones ambientales y de otros factores. En estos casos, el empleo de un solo testigo resistente y otro susceptible no es suficiente para determinar con exactitud el nivel de resistencia de los materiales en estudio. La disponibilidad de controles con distintos niveles de resistencia permitiría realizar un fenotipado más preciso. Un grupo de investigadores del "Volcani Center" desarrollaron una escala compuesta por siete líneas con diversos niveles de resistencia a TYLCD, introgresada a partir de distintas especies silvestres. En el marco de esta tesis se evaluó el comportamiento de esta escala en siete ensayos distintos, cuatro de ellos llevados a cabo en el COMAV-UPV y los otros tres en el Instituto Nacional de Ciencias Hortícolas de Cuba. Se compararon dos aislados de TYLCV (Tomato yellow leaf curl virus), una de las especies causantes de TYLCD, diferentes métodos de inoculación, dos estados de desarrollo de la planta y distintas condiciones ambientales. Los síntomas fueron más leves que los obtenidos en las condiciones ensayadas por los autores que desarrollaron la escala, si bien el orden de las líneas en la escala se mantuvo, con pocas excepciones. Sin embargo, en la mayor parte de las condiciones, la respuesta obtenida no correspondió a una escala gradual, ya que se observó una gran diferencia entre los valores de síntomas de las líneas susceptibles y las resistentes, siendo muy pequeñas las difer / Accession S. peruvianum PI 126944 has been reported as resistant to several biotic stresses, among them to Tomato yellow leaf curl disease, (TYLCD). In previous works carried out in the "Instituto Universitario para la Conservación y Mejora de la Agrodiversidad Valenciana" (COMAV) three interspecific hybrids between this accession and cultivated tomato were obtained, using immature seeds rescue. In subsequent works more advances generations from these materials were developed, including until the pseudo-F6 generations and backcrosses to the cultivated species of some of the pseudo-Fn generations. With the aim of taking advantage of these materials in the improvement of cultivated tomato, in previous works of the group, the development of a set of Introgression lines (ILs) that contain the genome of the accession PI 126944 in the genetic background of S. lycopersicum was initiated. The obtaining of a large number of descendants is necessary in order to have correctly represented the genome of the donor species, thus there is the need to optimize the protocols In this sense, the first aim of this work was the study of several factors involved in the overcoming of the incompatibility barriers, to obtain a high number of descendants and maximize the probability of introgressing the genome of PI 126944 in the set of ILs. Three backcross assays were carried out, initiated with different plants of the generations pseudo-F4, pseudo-F5 and pseudo-F6. The parental genotype resulted a determinant factor in the obtaining of descendants, so the recommendation is the use of the maximum number of different genotypes, in order to maximize the probability of obtaining progeny. A proof of different culture media was carried out, which allowed the selection of the better combination of auxins and cytokinins to grow immature seed and regenerate plants. The effect of the number of days from pollination to fruit harvest was also studied. As mentioned before, the collection of ILs results of interest, given the resistance of the donor parental to TYLCD, among others traits. Once the collection is completed, it will be evaluated for its resistance to this disease. The previous studies showed that it is probably a quantitative resistance, whose expression is often more dependent of the environmental conditions and of other factors. In these cases, the use of only one resistant and one susceptible control is not sufficient to determine with accuracy the level of resistance. Availability of controls with different levels of resistance would allow a more precise phenotyping. A group of researchers of the "Volcani Center" developed a scale that consisted of seven lines with different levels of resistance to TYLCD, introgressed from different wild species. In this work, the response of this scale in seven distinct assays was evaluated, four of them carried out in the COMAV-UPV and the others three in the "Instituto Nacional de Ciencias Hortícolas de Cuba". Two isolates of TYLCV (Tomato yellow leaf curl virus), one of the species causing TYLCD, different inoculation method, two development stages of the plant and several environmental conditions were evaluated. In general, the symptoms were more slight that the obtained in the conditions assayed by the authors that developed the scale, although the order of the lines in the scale were maintained, with few exceptions. However, in most of the conditions, the response obtained did not correspond to a graded scale, since there were high differences among the symptom scores of the susceptible and the resistant lines, with very small the differences among the resistant lines. These results suggest the possibility to reduce the number of lines to employ in each concrete condition, selecting the most susceptible, the most resistant and another with intermediate levels of resistance. / L'entrada PI 126944 de S. peruvianum ha sigut descrita com a resistent a diferents estresses biòtics, entre ells a la malaltia de l'arrissat groc de la tomaca (Tomato yellow leaf curl disease, TYLCD). En treballs previs realitzats en el "Instituto Universitario para la Conservación y Mejora de la Agrodiversidad Valenciana" (COMAV) es van obtenir tres híbrids interespecífics entre aquesta entrada i la tomaca cultivada, emprant el rescat de llavors immadures. En treballs posteriors, es van desenvolupar generacions més avançades a partir d'aquests materials, incloent fins a les generacions pseudo-F6 i retrocreuaments cap a l'espècie cultivada d'algunes de les generacions pseudo-Fn. A fi de aprofitar aquests materials en la millora de la tomaca cultivada es va iniciar, en treballs anteriors del grup, el desenvolupament d'un conjunt de línies d'introgressió (Introgression lines, ILs) que continguen el genoma de l'entrada PI 126944 en el fons genètic de S. lycopersicum. Per a tenir correctament representat el genoma de l'espècie donant en el fons genètic de la tomaca és necessari obtenir un gran nombre de descendents, per la qual cosa és necessari optimitzar els protocols. El primer objectiu d'aquesta tesi va ser l'estudi de diferents factors implicats en la superació de les barreres d'incompatibilitat, a fi d'aconseguir un elevat nombre de descendents i maximitzar la probabilitat d'introgressar el genoma de PI 126944 en el conjunt de ILs. Es van dur a terme tres assajos de retrocreuament, iniciats amb diferents plantes de les generacions pseudo-F4, pseudo-F5 i pseudo-F6. El genotip dels parentals va resultar un factor determinant en l'obtenció de descendència, per la qual cosa es recomana utilitzar el màxim nombre de genotips diferents, a fi de maximitzar la probabilitat d'obtenir descendència. Es va dur a terme una prova de medis de cultiu que va permetre seleccionar la combinació més adequada d'auxines i citoquinines per al cultiu de llavors immadures i posterior regeneració de plantes. Es va estudiar l'efecte del nombre de dies transcorreguts des de la pol·linització fins a la recol·lecció dels fruits, havent-se obtingut resultats diferents. Tal com s'ha comentat anteriorment, aquesta col·lecció de ILs presenta interès per la resistència del parental donant a TYLCD. Una vegada es complete la col·lecció, s'avaluarà per la seua resistència a aquesta malaltia. Els estudis previs han mostrat que es tracta probablement d'una resistència quantitativa, l'expressió de la qual sovint és més depenent de les condicions ambientals i d'altres factors. En aquests casos, l'utilització d'un sol control resistent i un altre susceptible no és suficient per a determinar amb exactitud el nivell de resistència dels materials en estudi. La disponibilitat de controls amb diferents nivells de resistència permetria realitzar un fenotipat més precís. Un grup d'investigadors del "Volcani Center" van desenvolupar una escala composta per set línies amb diversos nivells de resistència a TYLCD, introgressada a partir de diferents espècies silvestres. En el marc d'aquesta tesi es va avaluar el comportament d'aquesta escala en set assajos diferents, quatre d'ells duts a terme en el COMAV-UPV i els altres tres en el "Instituto Nacional de Ciencias Hortícolas de Cuba". Es van comparar dos aïllats deTYLCV (Tomato yellow leaf curl virus), una de les espècies causants de TYLCD, diferents mètodes d'inoculació, dos estats de desenvolupament de la planta i diferents condicions ambientals. Els símptomes van ser més lleus que els obtinguts en les condicions assajades pels autors que van desenvolupar l'escala, si ben l'ordre de les línies en l'escala es va mantenir, amb poques excepcions. No obstant açò, en la major part de les condicions, la resposta obtinguda no va correspondre a una escala gradual, ja que es va observar una gran diferència entre els valors de símptomes de les línies susceptibles i les resiste / Campos, GN. (2018). Aprovechamiento de las especies Solanum peruvianum en la mejora del tomate [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/100858 / Compendio

L'introgression est un processus fréquent et qui a d'importantes conséquences évolutives. L'objectif de ce travail était de tester un modèle neutre d'introgression chez des épicéas du Plateau tibétain et des régions voisines. Le travail a permis de mettre en évidence que la direction de l'introgression pouvait être prédite par la dynamique passée des populations d'arbres, et que l'importance de cette introgression était inversement proportionnelle à l'intensité des échanges génétiques au sein de l'espèce invasive, grâce à la comparaison de la structure génétique basée sur des marqueurs chloroplastiques (à hérédité paternelle) et mitochondriaux (à hérédité maternelle). / Introgression is a widespread phenomenon with potentially profound evolutionaryconsequences. Recently, significant progress in our understanding of introgression hasbeen made with the development of a neutral model. This model predicts that, whenone species invades an area already occupied by a related species, introgression ofneutral genes takes place mainly from the local species towards the invading ones. Inaddition, following a contact between two hybridizing species, the model predicts thatintrogression should be particularly frequent for genome components experiencinglittle gene flow. However, to date, there was no empirical example available, in whichone species expanded into the range of a closely related one and two markers withcontrasted rates of gene flow had been studied for both species. Only in such a casecould the two predictions outlined above be tested simultaneously. In addition, basedon these two predictions, species delimitation should be more efficient when usingmolecular markers experiencing high rates of gene flow. The present thesis was designed to test the hypotheses of this model. The biologicalmodel used was conifers, a group in which introgression and hybridization arecommon because of incomplete reproductive isolation. The species investigatedbelong to the genus Picea (spruce). We focused on two species complexes,represented by monographic clades in a phylogenetic study using the chloroplast genematK. All species studied occur in the Qinghai-Tibetan Plateau (QTP) and adjacenthighlands. The phylogeography of these species complexes was reconstructed usingorganelle markers (mitochondrial DNA, mtDNA and chloroplast DNA, cpDNA). Inconifers, mtDNA and cpDNA have contrasted modes of inheritance. The former ismaternally inherited, transmitted by seeds experiencing little gene flow while thelatter is paternally inherited, transmitted by both pollen and seeds experiencing highlevels of gene flow. Therefore, uniparentally inherited mtDNA and cpDNA markersexperience different rates of gene flow in such a group, providing an ideal model to test the relationship between rates of gene flow, introgression and species delimitation.Two mtDNA fragments (nad1intron b/c; nad5 intron1) and three cpDNA fragments(ndhK-C；trnL-trnF；trnS-trnG) were sequenced for nine species belonging to thePicea asperata and P. likiangensis species complex.(1) Nine mtDNA and nine cpDNA haplotypes were detected in 459 individualsfrom 46 natural populations in five species of P. asperata complex. As found in mostconifer species studied so far, low variation is present in the two mtDNA intronsalong with a high level of differentiation among populations (GST = 0.90). In contrast,higher variation and lower differentiation among populations was found at cpDNAmarkers (GST = 0.56). The cpDNA, although far from being fully diagnostic, is morespecies-specific than mtDNA: four groups of populations were identified usingcpDNA markers, all of them related to species or groups of species, whereas formtDNA, geographical variation prevails over species differentiation. A literaturereview shows that mtDNA variants are often shared among related conifer species,whereas cpDNA variants are more species-specific. Hence, increased intraspecificgene flow appears to decrease differentiation within species but not among species.[...]

Les invasions biologiques sont reconnues comme un facteur évolutif important sur une échelle de temps courte. Elles affectent notamment la structure génétique des populations, les patrons d’évolution phénotypique et la richesse des faunes de parasites associées aux populations envahissantes. Cette étude se propose de quantifier les conséquences d’une invasion biologique suivant ces trois niveaux (génétique, phénotypique et parasitologique) en prenant pour exemple le cas du tilapia du Mozambique Oreochromis mossambicus. Ce cichlidé africain présente un statut remarquable en biologie de la conservation puisqu’il est à la fois (i) l’une des espèces les plus envahissantes au monde car dispersée à l’échelle globale au cours du XXème siècle et (ii) une espèce « quasi-menacée » (UICN) sur son aire native (partie du sud-est de l’Afrique) du fait de son hybridation massive avec d’autres Oreochromis sp. introduits. La démarche générale employée ici est de décrire l’histoire récente des populations à l’aide de marqueurs nucléaires (AFLP) et des séquences de l’ADN mitochondrial (ADNmt), puis de mettre en relation ces résultats génétiques avec la diversité morphologique et la parasitologie des populations. Deux systèmes différents ont été étudiés : Au sein de l’aire native, l’étude se focalise sur le Limpopo inférieur et le sous-bassin de la Changane (Mozambique). Des patrons d’introgression incluant trois espèces en présence sont détectés, mais les hybrides sont peu fréquents et leur expansion limitée. Ces résultats sont de plutôt bonne augure pour la conservation d’O. mossambicus et ils permettent d’identifier deux zones de conservation prioritaires. L’étude des parasites indique une plus grande diversité parasitaire mais de faibles prévalences dans les sites de moindre valeur en conservation, ce qui pourrait favoriser le succès des espèces introduites et de leurs hybrides. Parmi les territoires envahis, les AFLP et l’ADNmt soutiennent une homogénéité générale et une diversité génétique faible, qui sont interprétées comme le résultat d’un fort goulot d’étranglement précédant l’expansion à l’échelle mondiale. Une structure des populations en lien avec la géographie à large échelle (Nouvelle-Calédonie, Guadeloupe, Jamaïque) est cependant détectée. La variation de la forme du corps est également structurée à large échelle géographique, ce en dépit des fortes variations environnementales enregistrées à l’échelle locale. Cela suggère un effet des contraintes génétiques sur la diversification morphologique contemporaine. L’absence de parasites monogènes sur les populations introduites en Nouvelle-Calédonie peut être mise en relation avec un évènement fondateur, et est proposé comme l’un des facteurs ayant pu favoriser le succès de l’espèce. En conclusion, une faible diversité génétique ne contraint vraisemblablement pas un potentiel envahissant élevé et une diversification rapide chez les tilapias. / Biological invasions are recognized as a significant evolutionary factor over short time scales. In particular, their effect is well recorded on the genetic structure of populations, the patterns of phenotypic evolution and the richness of parasite fauna associated to invasive populations. This study aims at quantifying the consequences of a biological invasion according to these three levels (genetical, phenotypical and parasitological) taking as example the Mozambique tilapia Oreochromis mossambicus. This African cichlid is characterized by an unusual conservation status since it is both (i) ranked among the world’s worst invasive species due to its global dispersion during the 20th century and (ii) sorted as “near-threatened” (IUCN) over its native range (a part of south-east Africa) because of massive hybridization with alien introduced Oreochromis species. The approach used in this study imply to describe the recent history of populations using nuclear (AFLP) and mitochondrial DNA (mtDNA) markers, and then to compare this genetic background to results describing the morphological and parasitological diversity of populations. Two different biological systems were studied: 1) Within the native range, the study focuses on the Lower Limpopo and the Changane sub-drainage (Mozambique). Introgression patterns involving the three co-occurring species were detected, but the frequency of hybrid is low and their geographic expansion is limited. These results provided rather good auspices for the conservation of O. mossambicus, and they allowed to identify two zones of high conservation priorities. The parasitological survey reveals high parasite richness and low prevalences among sites of low conservation values. This last pattern could favour the success of alien introduced species and their hybrids. 2) Among the invasive range of O. mossambicus, both AFLP and mtDNA support a strong genetic homogeneity and a low genetic diversity, a pattern interpreted as resulting from a strong population bottleneck preceding the events of global dispersion. A pattern of population structure related to large scale geography (New Caledonia, Guadeloupe, Jamaica) is nevertheless detected. Body shape variation is also primarily structured at large geographical scale, suggesting a role for genetic constrains on contemporary morphological diversification. The total absence of monogenean parasites in the populations of New Caledonia could result from a founding event and is suggested as a potential factor that could have favoured the O. mossambicus’ success. In conclusion, a low genetic diversity does not likely constraint a strong invasive potential and a rapid phenotypic diversification in tilapias.

Helicobacter pylori est associée à des pathologies gastro-duodénales sévères mais est également un marqueur bactérien de migrations humaines. Nous avons montré que des populations génétiques distinctes de H. pylori ont accompagné au moins quatre migrations en Asie du sud-est et en Océanie : i) une expansion des ancêtres des austronésiens il y a 5000 ans à partir de Taiwan en Océanie, ii) une migration d’Inde en Asie du sud-est depuis 2000 ans,iii) une migration des ancêtres des locuteurs des langues austro-asiatiques au Vietnam et auCambodge il y a 4000 ans, i) une migration des ancêtres des Thaïs du sud de la Chine vers l’actuelle Thaïlande au début du second millénaire. Ces données confirment la résolution plus élevée de la diversité génétique de H. pylori pour retracer les anciennes migrations humaines par comparaison aux marqueurs génétiques humains traditionnels. Nous avons ensuite investigué les facteurs de virulence de souches isolées de patients présentant des symptômes gastriques au Sénégal et au Cambodge. Au Sénégal, une association significative a été observée entre le cancer gastrique et le gène cagA, deux motifs EPIYA-C et l’allèle vacA s1. De multiples segments EPIYA-C étaient observés moins fréquemment que dans les autres régions du monde, contribuant probablement à la faible incidence du cancer gastrique. Au Cambodge, une introgression fréquente d’allèles cagA et vacA européens dans des souches d’Asie de l’est a été observée. CagA et VacA ayant des effets antagonistes, cette expansion pourrait entraîner la rupture de l’équilibre entre les effets biologiques de ces deux protéines et être responsable de conséquences graves sur l’évolution de la maladie. / Helicobacter pylori is associated with severe gastroduodenal disorders but is also a bacterial genetic marker of human migrations. First, we provide evidence that distinct H. pylori genetic populations accompanied at least four ancient human migrations into Oceania and Southeast Asia: i) an expansion of Austronesian speaking people about 5000 years ago from Taiwan into Oceania, ii) a migration from India into Southeast Asia within the last 2000 years, iii) a migration of Austro-Asiatic speaking people into Vietnam and Cambodia about 4000 years ago, and iv) a migration of the ancestors of the Thai people from Southern China into Thailand during the early second millennium AD. These findings demonstrate that H. pylori genetic diversity has more discriminatory power than traditional human genetic markers for tracing old human migrations. Second, we investigated virulence factors of H. pylori strains isolated from patients with gastric symptoms in Senegal and Cambodia. In Senegal, a significant association was observed between gastric cancer and the cagA gene, two EPIYA-C segments, and the s1 vacA allele in Senegal. Multiple EPIYA-C segments were less frequent than reported in other countries, possibly contributing to the low incidence of gastric cancer. In Cambodia, the frequent introgression of European vacA and cagA alleles into East Asian H. pylori strains was observed. As VacA and CagA have opposing effects, this expansion may disrupt the balancing activities on epithelial cells which might result in severe consequences for individual disease outcome.