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TYLCV is one of the most damaging viruses transmitted by the whitefly Bemisia tabaci. This virus, that causes severe symptoms on tomato culture, had spread for about 10 years in several parts of the world. To date, the possible transport of the virus by the way of imported and exported tomato fruits had never been considered. In this study, we report that TYLCV is present in tomato fruits at high titre. The virus can be acquired by 5 to 15% of whiteflies that fed on tomato fruits, depending on the acquisition access period, and then be transmitted up to 8% to tomato plants. The potential risk of causing new outbreaks of TYLCV via infected tomato fruits as a virus source is discussed.

L'hybridation somatique permet d'accroître la diversité utile des complexes d'espèces, d'une part en contournant les incompatibilités ou contraintes sexuelles et d'autre part en combinant les génomes nucléaires, chloroplastiques et mitochondriaux suivant de nouvelles règles. Elle trouve des applications importantes chez les agrumes compte tenu du caractère apomictique ou de la stérilité de nombreux cultivars, de la structure du complexe d'espèces et des programmes de manipulation de la ploïdie visant la sélection de cultivars triploïdes aspermes. Ces applications sont illustrées par les résultats obtenus par le Cirad et ses partenaires, par électrofusion de protoplastes. 1. Diversification du groupe des mandariniers au niveau triploïde: les génomes de cultivars inexploitables par voie sexuée ont été intégrés au sein d'hybrides tétraploïdes. Cette manipulation de la ploidie, via l'hybridation somatique, a enrichit très significativement le compartiment tétraploïde du complexe d'espèces. Cette technique a également permis la synthèse directe d'hybrides triploïdes par fusion de protoplastes haploïdes et diploïdes. 2. Création de porte-greffe résistants aux contraintes biotiques et abiotiques: l'addition de l'ensemble des gènes des deux parents quels que soient leurs niveaux d'hétérozygotie trouve une application majeure pour la création de porte-greffe cumulant des caractères de résistance. Un hybride intergénérique P. trifoliata + C. deliciosa s'avère ainsi très prometteur pour les zones où sont associées Tristeza (maladie virale) et contraintes calcaires ou salines. 3. Exploitation de la diversité de genres sexuellement incompatibles: cette application est moins convaincante compte tenu des difficultés de régénération et de l'instabilité des génomes nucléaires révélée par les analyses de marquage moléculaire. A ce niveau, la mise en oeuvre de programmes d'hybridations asymétriques paraît souhaitable pour n'introgresser que quelques fragments du génome des espèces sauvages. 4. Interactions noyaux/cytoplasmes: l'obtention, par hybridation symétrique, d'alloplastes diploïdes et d'hybrides tetraploïdes dans différents contextes cytoplasmiques, ouvre la voie à l'étude des interactions nucléo-cytoplasmiques.

Genetic relationships among 92 individuals of 8 more economically representative species of Citrus (C. reticulata, C. sinensis, C. aurantium, C. paradisi, C. maxima, C. lemon, C. aurantifolia and C. medica) and 17 other species are estimated by the amplification of 10 loci of SSR named STMS (Sequence Tagged Microsatellites). The potential of STMS for cultivar identification in each species has been evaluated and we have performed a neighbour joining analysis in the basis of a dissimilarity matrix among the different genotypes. Polymorphism of 8 STMS was sufficient to obtain genetic aggregations where three main groups were clearly identified: the orange-mandarin group, the pummelo-grapefruit group and the lime-citron-lemon group. The Citrusspecies relationships were in broad agreementwith those established by previous analyses based on molecular markers and morphological traits, suggesting that SSR data will be useful for exploring intra-generic Citrus genetic taxonomy. The studied microsatellites have not allowed distinguishing varietieswithin some of the species known to have evolved by somatic mutations like sweet oranges and sour oranges. However, polymorphism is detected among lemon varieties.

Since 1994, INRA and CIRAD-FLHOR are associated for an easy peeler citrus improvement program by selecting spontaneous triploid hybrids resulting from crosses between Clementine and other citrus species. These triploid plants arose from gametic cell fusion between a haploid gamete and an unreduced diploid one. It is essential Io identified the 2n gamete parent and the mode of nuclear restitution involved in the diplogamy. For this purpose we have used codominant molecular markers (isozymes, STMS) and dominant ones (RAPDs, AFLPs) to detect qualitative polymorphism and quantitative variations among DNA of more than 100 selected triploid citrus, We showed that codominant markers can be used Io détermine the 2n gamete parental origin and the mode of nuclear restitution, whereas, dominant markers can only be used Io estimate the mode of nuclear restitution. Among the analyzed triploid hybrids, we find that 2n ovum production is very frequent, and 2n pollen production seems to be rare (less than 2%), The mode of nuclear restitution which was identified by estimating homozygousity level among the triploid progenies is probably a Second Division Restitution (SDR). The implications of this origin of 2n gametes for easy peeler breeding strategies are discussed.

Genetic information of plant cytoplasmic DNA presents a great interest for phylogenic studies. Recently, in Citrus, a new interest for cytoplasmic genome analysis has resulted from the impediment of somatic hybridization. Indeed this technique allows new patterns of nuclear, chloroplastic, and mitochondrial genomes that must be characterized. Cytoplasmic genome analysis among Citrus and related genera was generally done by Southern blots. This method is powerful but not applicable to in vitro plants because it requires too much fresh material. A few years ago we published a preliminary work that demonstrated the successful amplification of Citrus cytoplasmic DNA by using mitochondrial and chloroplastic universal primers and the possibility in some cases to display polymorphism by combining these amplifications with an enzymatic restriction. In the present work, the usefulness of such CAPS analysis, for cytoplasmic genome differentiation at the infra-generic level (Citrus) and intergeneric level inside of the Aurantioideae sub family, was studied on 44 genotypes from 31 species. With the combinations of primers and enzymes tested, the CAPS Technique appears more powerful for chloroplast than for mitochondria to display polymorphisms, even at the infra-generic level. Phylogenic inference are made from a cluster analysis of chloroplastic data obtained with 4 primers coupled each with 2 to 4 restriction enzymes. An example of application for somatic hybrid cytoplasmic genome characterization is presented.

Poncirus trifoliata (L.) Rat. and its hybrids are part of the citrus germplasm very useful for rootstock breeding. Taking into account the difficulties to isolate good quality protoplasts from leaves of field trees, the failure of nucellar embryogenic callus induction from these genotypes and the risk of zygotic plant recovery among the seedlings, il is important Io establish genetically certified in vitro fines for further protoplast isolation with the objective of developing new strategies involving somatic hybridization. Micropropagation allows the obtention of genetically homogeneous plantlets and il is a way to attain such kind of fines. However, it is important to control the genetic homogeneity of the micropropagated plants. Isozyme, sequence-tagged microsatellite sites (STMS), and flow cytometry analysis developed in various citrus species allow to control sonne major sources of variation such as zygotic origin of the explants or ploidy variafion. The résults of the usefulness of these techniques in the control of the genetic homogeneity of micropropagated shoots of Troyer citrange [Citrus sinensis (L.) Osb. x Poncirus trifoliala (L.) Rat.], Rubidoux trifoliate orange [Poncirus trifoliata (L.) Raf.], and Poncirus trifoliata var. Flying dragon are presented. The selected fines will be used in research works to continue the creation of new rootstocks through somatic hybridization.