PERFORMANCES OF NEW AFRICAN GERMPLASM OF THE YAM Dioscorea cavenensis-rotundata IN THE CARIBBEAN

Three polycrosses of D. cavenensis-rotundata introduced from IITA (Nigeria) have been selected in Guadeloupe over six years, with the contribution of trials in Martinique, St. Lucia, St. Vincent and Grenada. Several clones appear more adapted to an industrial cultivation than local controls. The selection process and the main characters involved are described. Prospects for the use of this material and the following steps in this first breeding of the African yam in the Caribbean are discussed

OBSERVATIONS SUR LA RESPONSE DE XANTHOSOMA SAGITTIFOLIUM A DES TRAITEMENTS GIBBERELLIQUES EN VUE DE SA FLORAISON

X. sagittifolium cv Malanga rouge a été traité !l 250 et 1500 ppm avee de la gibberelline en 1983. La floraison a atteint 99% avec 250 ppm meilleur traitement. Mais, en 1984, ce même traitement a été décevant sur oe cultiva comme sur d'autres. Faut-il en rendre responsable l'infestation du terrain par Pythium myriotylum an agent de d{périssement du Malanga? Par ailleurs, de d€formations des rhizomes secondaires c:onsecutives au traitement gibberelliqm.• apparaissent affecter la génération végétative suivante. ----- X. sagittifolium cv Malanga rouge was treated in 1983 with 250 and 1500 ppm gibberellic acid. Flowering reached 99% with 250 ppm which was the best treatment. But, in 1984, this same treatment was disappointing over this cultivar as well as on others, Can this be related to the plot infestation by Pythium myriotylum, an agent of the tannia leaf burning disease? Meanwhile, deformations of secondary rhizomes resulting from the gibberellic treatment seem to affect the next vegetative generation

Data on the sexual reproduction and the possibilities of breeding new varieties in Dioscorea alata and Dioscorea cayenensis rotundata

Après une brève description des inflorescences, nous passerons en revue les différentes limites que nous avons pu recenser à la recombinaison sexuée. Enfin, nous envisagerons les solutions et les perspectives en matière de sélection créatrice. ----- After a brief description of the inflorescence, the different limitations found in sexual recombination will be reviewed. Finally, the solutions and prospects in the field of breeding will be considered

OBTENTION DE PLANTULES D'IGNAME (D. alata ET D. cayenensis-rotundata) PAR CULTURE D'EMBRYONS IN VITRO

La culture d'embryon joue un rôle croissant dans l'amélioration des plantes. L'amélioration de l'igname n'en bénéficie pas encore. Des embryons de D. cayenensis-rotundata hybrides et d'une variété traditionnelle de D. alata ont été prélevés après désinfection et cultivés sur un milieu de Murashige et Skoog modifié. La germination des embryons a été obtenue. Les plantules sont au stade 3-4 feuilles pour D. alata ; celles de D. cayenensis sont en partie au champ. Si l'origine de celles-ci ne pose pas de problème, l'origine des plantules de D. alata en pose. Différentes hypothèses d'interprétation et les perspectives de valorisation de la technique sont discutées. ----- In vitro culture of embryo is playing an increasing part in plant breeding. Yam improvement is not yet benefiting from. Embryos of D. cayenensis-rotundata hybrids and of a traditional variety of D. alata have been picked, desinfected, then cultivated on a modified MS media. Embryo germination has been obtained. Plantlets have reached stage 3-4 leaves for D. alata and those of D. cayenensis-rotundata are partially in the field. If as for this last ones their origin are not problematic, question stand for the D. alata ones, Different hypothesis of interpretation and prospects for valorization of the technics are discussed

DYNAMIQUE DES POPULATIONS D'U N NEMATODE (Pratylenchus coffeae) DANS LES IGNAMES EN COURS DE CONSERVATION

La dynamique des populations de Pratylenchus coffeae dans les tubercules de Dioscorea cayenensis du type «Grosse caille» est décrite en cours de culture, à la récolte et lors de la conservation sur les populations d'endoparasites est analysée. La répartition des nématodes le long du tubercule est suivie dans le temps et les risques de contamination de la culture suivante sont présentés. Une méthode non destructive d'échantillonnage des nématodes, par biopsie du parenchyme cortical des tubercules, est proposée : elle permet une évaluation des niveaux d'infestation des tissus vivants et autorise la plantation des semenceaux sans en altérer la germination. Les méthodes d'extraction des nématodes sont comparées (entonnoir de BAERMANN versus centrifugation) pour un diagnostic rapide. Différentes stratégies de contrôle de Pratylenchus sont proposées. ----- Population dynamics of the root-lesion nematode ( Pratylenchus coffeae) is followed in the tubers of Dioscorea cayenensis from the plantation in the field until the end of the storage. The impact of various conservation conditions is evaluated on the nematode's reproduction. The distribution of parasites inside the tuber is described and the contamination risk for a new production cycle are underlined. A non-destructive sampling method is proposed by biopsy of the tubers : it allows nematological studies and succesfull replantation of the analysed tubers. Nematode extraction methods are compared (BAERMANN funnel versus centrifugation) in a diagnostic purpose. Different control strategies of Pratylenchus are proposed

SENSIBILITE DE CULTIVARS DE Dioscorea alata, D. cayenensis ET D. trîfida AUX NEMATODES Meloidogyne incognita, Pratylenchus coffeae ET Scutellomena bradys

Un test précoce de sensibilité aux nématodes est proposé sur jeunes plantules issues de graines, de boutures de tiges et de vitro-plants. Une image globale des sensibilités de trois espèces d'ignames (Dioscorea alata, D. cayenensis, D. trîfida ) au parasitisme contrôlé de trois nématodes (Meloidogyneincognita, Pratylenchus coffeae, Scutellonema bradys) a été obtenue à partir de vitro-plants de diverses variétés. La variété «Plimbite» (D. alata) parait nettement intéressante et quelques plants de D. cayenensis issus de graines du Nigéria semblent résistants àP. coffeae. EVALUATION OF SUSCEPTIBILITES OF YAM CULTIVARS (D. alata, D. cayenensis, D. trîfida) TO SOIL NEMATODES : Meloidogyne incognita, Pratylenchus coffeae AND Scutellonema bradys An early susceptibility test is proposed on young plants obtained from seeds, stem cuttings and vitro-plants. An analysis of the resistance of various yam cultivars to the 3 most important parasitic nematodes (Meloidogyne incognita, Pratylenchus coffeae, Scutellonema bradys) is given through controlled inoculations in greenhouse conditions on vitroplants and seedlings. «Plimbite», a D. alata variety, seems most interesting and some nigérian seedlings of D. cayenensis appear resistant to P. coffeae

Genetic diversity of the greater yam (Dioscorea alata L.) and relatedness to D. nummularia Lam. and D. transversa Br. as revealed with AFLP markers

UMR DAPInternational audienceAmplified fragment length polymorphism markers were used to assess the genetic relatedness between Dioscorea alata and nine other edible Dioscorea. These species include D. abyssinica Hoch., D. bulbifera L., D. cayenensis-rotundata Lamk. et Poir., D. esculenta Burk., D. nummularia Lam., D. pentaphylla L., D. persimilis Prain. et Burk., D. transversa Br. and D. trifida L. Four successive studies were conducted with emphasis on the genetic relationship within D. alata and among species of the Enantiophyllum section from Vanuatu. Study 1 was carried out to select a set of polymorphic primer pairs using 11 combinations and eight species belonging to five distinct sections. The four most polymorphic primer pairs were used in study 2 among six species of the Enantiophyllum section. Study 3 focussed mainly on the genetic relationship among 83 accessions of D. alata, mostly from Vanuatu (78 acc.) but also from Benin, Guadeloupe, New Caledonia and Vietnam. The ploidy level of 53 accessions was determined and results indicated the presence of tetraploid, hexaploid and octoploid cultivars. Study 4, included 35 accessions of D. alata, D. nummularia and D. transversa and was conducted using two primer pairs to verify the taxonomical identity of thecultivars ‘langlang’, ‘maro’ and ‘netsar’ from Vanuatu. The overall results indicated that each accession can be fingerprinted uniquely with AFLP. D. alata is an heterogeneous species which shares a common genetic background with D. nummularia and ‘langlang’, ‘maro’ and ‘netsar’. UPGMA cluster analysis revealed the existence of three major groups of genotypes within D. alata, each assembling accessions from distant geographical origins and different ploidy levels. The analysis also revealed that ‘langlang’, ‘maro’ and ‘netsar’ clustered together with the cultivar ‘wael’ (D. transversa) from New Caledonia. Results are discussed in the pape