Introduction. Le plantain constitue une importante denrée alimentaire pour de nombreuses populations au sud du Sahara. Sa production dans les systèmes traditionnels de culture par les petits paysans est menacée par la maladie des raies noires, une maladie foliaire due à Mycosphaerella fijiensis Morelet responsable de pertes importantes de récolte. Pour faire face à cette maladie, des hybrides tétraploïdes de type plantain, résistants à la maladie, ont été créés au Cameroun puis sélectionnés à l’issue d’une première phase d’évaluation. Après multiplication végétative, les hybrides ainsi sélectionnés ont été évalués en station de recherche afin de déterminer leurs caractéristiques agronomiques et leur rendement potentiel en conditions de culture semi-intensive. Matériel et méthodes. De 1996 à 2000, trente hybrides sélectionnés ont été évalués, en comparaison avec leurs parents femelles, sur deux cycles de production à la faveur de trois essais mis en place suivant un dispositif expérimental en blocs de Fisher complètement randomisés avec deux répétitions de 10 bananiers chacun. Chacun des bananiers a été étudié à partir de caractéristiques agronomiques portant sur la croissance et la production. Résultats et discussion. Sept hybrides ont été sélectionnés sur la base de leur rendement potentiel élevé, de leur précocité de floraison et de leur pouvoir rejetonnant. Cependant, ce matériel végétal tétraploïde présente plusieurs défauts qui constituent un frein à leur diffusion. Certains de ces hybrides sont utilisés comme produits intermédiaires dans un nouveau schéma d’amélioration variétale au CARBAP.

Introduction. The worldwide production of banana and plantain, which is estimated to 106 Mt·year–1, relies on a narrow genetic basis. Thus, banana production is fragile regarding emergent diseases, and creation of new varieties of banana stands out as a real necessity for its sustainability. In banana, various improvement strategies aim to create triploid hybrids. The objective of this report is to present a simple in vitro methodology to induce stable tetraploid plants by colchicine treatment, usable as parent for obtaining triploid varieties. Materials and methods. Twenty-one diploid M. acuminata clones and three interspecific M. acuminata / M. balbisiana diploid clones were treated as proliferating culture in liquid medium with 1.25 mM of colchicine for 48 h. Plant screening has been performed by morphological identification in greenhouse, chromosome counts on root tips and flow cytometry on leave blades on vitroplants using propidium iodide staining. Results. Chromosome counts led to distinguish diploid and tetraploid plants but did not afford to detect chimeras. Flow cytometry allowed an early screening of a larger number of plants leading to detect rapidly chimerical plants. It was observed that some stable 2x / 4x cytochimeras are periclinal. Tetraploid clones were obtained with all diploid genotypes. General behaviour of tetraploids in the field was globally weaker than the corresponding diploids. Nevertheless, all the doubled-diploids flowered and crossed with diploid plants to obtain triploid progenies. Conclusion. This study has clearly shown that induction of stable doubled-diploid plants can be obtained from a wide range of genetically different bananas. These results open the way to the systematic use of doubled-diploids by banana breeding programs for the release of enhanced triploid varieties.

Cold shocks and hydrostatic pressure shocks, respectively, were applied for the induction of bothtriploidy and tetraploidy in the common carp. Cold shocks of 0-2 °C, lasting 40 minutes and starting 2–5 minutes after the activation of gametes and hydrostatic pressure shocks with 1-3-5 minute exposures at 49.03–56.88 MPa (i. e. 7 116-8 225 psi – pounds per square inch), starting 5 minutes after the activation of gametes gave the best results. The tetraploidy induction by cold shocks or hydrostatic pressure shocks resulted either in negligible (1.54%), or in zero yields, respectively. The applicability of particular types of ploidy manipulation and the standardization of shock initiation were discussed.

Enzymatic polymorphism was studied in nine enzyme systems of four species of large AfricanBarbus (B. bynni occidentalis Boulenger, 1911; B. sacrutus Daget, 1963; B. petitjeani Daget 1962; and B. wurtzi Pellegrin, 1908), two species of small African Barbus (B. guineensis Pellegrin, 1913 and B. cadenati Daget, 1962), and two species of European Barbus (B. barbus Linnaeus, 1758 and B. meridionalis). Like European Barbus, the large African Barbus were found to express more than 20 enzymatic loci for these systems (21 to 23), whereas the small African Barbus only expressed 14. This result suggests that large African Barbus are tetraploid like European Barbus and that small African Barbus are diploid like the Asian species. The two groups of African Barbus do not appear to be phylogenetically closer to each other than they are to European Barbus. Consequently, tetraploidi-zation must have occurred long ago in large African Barbus, and may correspond to the same event responsible for the origin of the European species.

Tetraploidy was induced in embryos of Ruditapes philippinarum by treating the eggs with cytochalasin B (CB). Two treatment times were found to be effective in inducing tetraploidy: 0 to 10 minutes after insemination (before formation of the first polar body) and 45 minutes after insemination (just before the first cleavage). Treatments, started 5 and 45 minutes after insemination, produced $64.4\pm7.8{\%}$ and $28.3\pm2.3{\%}$ tetraploid embryos, respectively, after 6 hours (on the average over 3 experiments). However, no tetraploids were detected in 4-month-old spat. Sperm entry delayed by the CB could be involved in induction of tetraploidy by early treatment.