Etude de la productivité et de la sensibilité de diverses variétés de tomate (Lycopersicon esculentum Mill) à la virose du jaunissement et de l’enroulement en cuillère des feuilles au Sénégal

Après l’oignon, la tomate est le plus important légume au Sénégal. Elle est très sensible au virus Tomato Yellow Leaf Curl (TYLCV). Quatorze variétés de tomate ont été testées pour évaluer leur productivité et leur résistance au TYLC à différents stades phénologiques (floraison, fructification et maturité) dans un dispositif en blocs complets randomisés comptant trois répétitions. Les résultats ont montré que le nombre de fruits/grappe a varié entre les variétés. La masse unitaire des fruits était plus élevée pour Bybal, Roma VF et Lety F1. La longueur des fruits de Thoriya et Lety F1 était plus importante. Roma VF et Bybal ont présenté les plus gros fruits. TY75 et Ponchita ont produit les rendements en fruits consommables les plus élevés. Roma VF et Lety F1 ont produit les rendements non consommables les plus élevés. Globalement, TY75 et Roma VF ont été plus productives. Une résistance au virus a été observée chez douze variétés et une forte sensibilité chez deux autres (Roma VF et Xina). Ces résultats pourraient intéresser les sélectionneurs, les firmes semencières et les agriculteurs dans leur choix de variétés de tomate à cultiver.Mots clés : Tomate, Lycopersicon esculentum, TYLCV, Sénéga

Genetic diversity in cocoa germplasm of southern Cameroon revealed by simple sequences repeat (SSRS) markers

The range of polymorphism of about 194 cocoa accessions collected in farms in Southern Cameroon during field surveys and 71 Trinitario and Upper Amazon clones available in genebanks on-station wasassessed using 13 SSR markers. The gene diversity, genetic differentiation and genetic similarities were analysed for the different populations. In total, 282 alleles were detected within all the populations studied. The farm accessions were strongly differentiated based on their geographical origin, with accessions coming from the East province clustering together with local Trinitario accessions from the genebank. Accessions from the Centre-South provinces clustered with Amazon and hybrid accessions, suggesting more uptake of seed garden materials in farms in these provinces. The genetic diversity parameters indicate that the farmers’ planting material is not highly diverse, and is genetically close to parental genotypes available in genebanks. However, some promising Upper Amazon clones (T-clones) that have also been used as parents of released hybrid varieties were genetically distant from the accessions. This result suggests that the progenies of these parents have so far been poorly used in the cocoa farms surveyed. The consequences of these findings for cocoa breeding in Cameroon are discusse

Inheritance of resistance to the panicle-feeding bug Eurystylus oldi and the sorghum midge Stenodiplosis sorghicola in sorghum

A study of the inheritance of sorghum resistance to head-bug Eurystylus oldi and midge Stenodiplosis sorghicola has been conducted from an F1-based complete diallel involving four parental lines (namely head-bug resistant Malisor 84-7 & 87W810, and susceptible S 34 & ICSV 197). The trial was conducted at Samanko, Mali, under both natural and artificial head-bug infestation, in one date of sowing (DOS) in 1995 and two DOS in 1996. Headbug visual damage scores (under both types of infestation) were indicated and analyzed in all these trials. Head-bug numbers under artificial infestation on the two DOS of 1996, and midge damage score under natural infestation on the second DOS of 1996 were recorded. All four parents confirmed their expected level of resistance to head-bugs, while ICSV 197 confirmed its resistance to midge. Diallel analyses showed that general combining ability (GCA) and thus additive gene effects were very important in the inheritance of resistance to both pests. Specific combining ability and maternal effects were generally of minor importance. Mean performance of the parents and their GCA effects were linked, which suggests high heritability. Head-bug resistant parents, Malisor 84-7 & 87W810, with high per se resistance and negative GCA should therefore be used in breeding for resistance to this pest, while for a similar reason, ICSV 197 should be used in breeding for midge resistance. Results concerning independance between resistance to head-bugs and to midge, are also discussed

Phenotyping progenies for complex architectural traits: a strategy for 1-year-old apple trees (Malus x domestica Borkh.)

International audienceThe aim of this study was to define a methodology for describing architectural traits in a quantitative way on tree descendants. Our strategy was to collect traits related to both tree structural organization, resulting from growth and branching, and tree form and then to select among these traits relevant descriptors on the basis of their genetic parameters. Because the complexity of tree architecture increases with tree age, we chose to describe the trees in the early stages of development. The study was carried out on a 1-year-old apple progeny derived from two parent cultivars with contrasted architecture. A large number of variables were collected at different positions and scales within the trees. Broad-sense heritability and genetic correlations were estimated and the within tree variability was analyzed for variables measured on long sylleptic axillary shoots (LSAS). These results were combined to select heritable and not correlated variables. Finally, the selection of variables proposed combines topological with geometric traits measured on both trunks and LSAS: (1) on the trunk, mean internode length, and number of sylleptic axillary shoots; (2) on axillary shoots, conicity, bending, and number of sylleptic axillary shoots born at order 3. The trees of the progeny were partitioned on the basis of these variables. The putative agronomic interest of the selected variables with respect to the subsequent tree development is discussed

Performance of Coffea arabica F1 hybrids in agroforestry and full-sun cropping systems in comparison with American pure line cultivars

Coffea arabica F1 hybrids derived from crosses between wild Sudan-Ethiopian and American cultivars and propagated by somatic embryogenesis have been obtained in Central America. These new hybrids considerably enhanced the genetic diversity of coffee in the region. We conducted 15 trials to assess whether using hybrids represents substantial genetic progress in terms of productivity in agroforestry and full-sun cropping systems. The new germplasm was grown in the same conditions as the best American cultivar (homozygous pure lines). The results showed that yields of hybrids were earlier and superior to those of American cultivars. The hybrids were also more stable than the American cultivars in all environments. In the agroforestry system, the mean yield of hybrids was 58% higher than that of the American cultivars, while the mean yield of hybrids in the full-sun system was 34% higher. Coffee-based agroforestry systems (AS) are considered effective in protecting the environment in the volcanic cordilleras of Central America. We found that introducing hybrids in coffee-based AS can considerably increase productivity. This finding could be a convincing argument to encourage coffee growers who have adopted the full-sun cropping system to return to agroforestry cropping systems. Finally, the conditions for large-scale dissemination of those new hybrids—which represent a major innovation for C. arabica cropping—was analysed