Domestication history and geographical adaptation inferred from a SNP map of African rice

African rice (Oryza glaberrima Steud.) is a cereal crop species closely related to Asian rice (Oryza sativa L.) but was independently domesticated in West Africa-3,000 years ago. African rice is rarely grown outside sub-Saharan Africa but is of global interest because of its tolerance to abiotic stresses. Here we describe a map of 2.32 million SNPs of African rice from whole-genome resequencing of 93 landraces. Population genomic analysis shows a population bottleneck in this species that began-13,000-15,000 years ago with effective population size reaching its minimum value-3,500 years ago, suggesting a protracted period of population size reduction likely commencing with predomestication management and/or cultivation. Genome-wide association studies (GWAS) for six salt tolerance traits identify 11 significant loci, 4 of which are within-300 kb of genomic regions that possess signatures of positive selection, suggesting adaptive geographical divergence for salt tolerance in this species

Resilience of rice (Oryza spp.) pollen germination and tube growth to temperature stress

Resilience of rice cropping systems to potential global climate change will partly depend on the temperature tolerance of pollen germination (PG) and tube growth (PTG). Pollen germination of high temperature-susceptible Oryza glaberrima Steud. (cv. CG14) and Oryza sativa L. ssp. indica (cv. IR64) and high temperature-tolerant O. sativa ssp. aus (cv. N22), was assessed on a 5.6–45.4 °C temperature gradient system. Mean maximum PG was 85% at 27 °C with 1488 µm PTG at 25 °C. The hypothesis that in each pollen grain, the minimum temperature requirements (Tn) and maximum temperature limits (Tx) for germination operate independently was accepted by comparing multiplicative and subtractive probability models. The maximum temperature limit for PG in 50% of grains (Tx(50)) was the lowest (29.8 °C) in IR64 compared with CG14 (34.3 °C) and N22 (35.6 °C). Standard deviation (sx) of Tx was also low in IR64 (2.3 °C) suggesting that the mechanism of IR64’s susceptibility to high temperatures may relate to PG. Optimum germination temperatures and thermal times for 1 mm PTG were not linked to tolerating high temperatures at anthesis. However, the parameters Tx(50) and sx in the germination model define new pragmatic criteria for successful and resilient PG, preferable to the more traditional cardinal (maximum and minimum) temperatures

Tourisme et croissance inclusive dans les pays en développement : cas du Bénin

L’objectif de cet article est d’analyser empiriquement les relations complexes entre le tourisme et la croissance inclusive au Bénin. Ainsi, dans un cadre de cointégration des variables, deux modèles de régression sont déployés successivement et un troisième dans un cadre de non-cointégration. Les données chronologiques du Bénin de 1990 à 2020 ont été utilisées. Les résultats de nos estimations ont prouvé que le tourisme impacte positivement la croissance économique à long terme. Cette relation se caractérise par un impact positif du tourisme sur la croissance économique de long terme, avec une croissance économique de 1,93% lorsque le tourisme évolue de 1% confirmant ainsi l’hypothèse de la croissance tirée par le tourisme. Les résultats montrent également l’existence au sens de Granger d’une causalité bidirectionnelle entre la spécialisation touristique et croissance économique. Ensuite, les résultats montrent aussi que la croissance du secteur touristique s’accompagne par un accroissement des activités des autres secteurs de l’économie à long terme. A court terme, elle stimule les secteurs agricole et industriel du Bénin. Par contre les services à court terme connaissent une contraction à court terme

Resistance of selected Oryza glaberrima landraces and their intra-specific breeding lines to Beninese Rice yellow mottle virus isolates

International audienceRice yellow mottle virus (RYMV) is a widespread and damaging pathogen, endemic to Africa and affecting rice in lowland, irrigated and upland ecologies. Yield losses of 10–100% have been recorded, depending on rice genotypes, time of infection, cropping system, vector abundance and isolate pathogenicity. Control measures for this disease are based mainly on cultural practices and the use of varietal resistance. Specifically, Oryza glaberrima, the cultivated African rice species, has provided several of the known resistance alleles/genes. In this study, 160 O. glaberrima landraces, 55 of their intra-specific progenies and two controls - Tog5681 (resistant) and IR64 (susceptible) - were screened against five RYMV isolates collected from Northern Benin. Disease severity was measured on plants at 21 and 42 days after inoculation. Two cultivars - IRGC104019 and IRGC96787 (Tog5644) - from Tanzania and Nigeria respectively - and 16 intra-specific lines were identified as highly resistant to all five isolates. The genotyping of IRGC104019 and IRGC96787 revealed that they share allele rymv1-3, identified in Tog5681 (the resistant control) and that confers resistance, bringing the number of O. glaberrima accessions known to date to harbor this allele to 11. The importance of this finding and the level of resistance displayed by these two accessions strengthen the hypothesis that the African rice collection is a potential RYMV resistance donor. It is, therefore, necessary to further screen it for valorizing its usefulness in breeding programs

Variation and Phenotypic Evaluation of Intraspecific Oryza glaberrima Lines Resulting from Crossings between Tog5681, Tog5672 and Tog7291

Rice cultivation in Africa suffers from various biotic and abiotic constraints. The African rice, Oryza glaberrima, is a potential source of useful genes for resistance to a range of these stresses. The development of interspecific varieties based on crosses between the high yielding cultivated Asian rice species (Oryza sativa) and O. glaberrima showed some gaps in the resistance compared to O. glaberrima. In order to valorize its genetic potential, intraspecific lines were developed using three O. glaberrima lines Tog5681, Tog5672 and Tog7291 as parents. Phenotypic evaluation of the progeny (total of 55 F6 lines) and checks (O. glaberrima and O. sativa) using 18 quantitative characters, showed a higher degree of variation in plant height, leaf dimensions, panicle fertility and grain weight. Based on the discriminating characters proposed here for further exploitation, intraspecific lines were grouped into five clusters, two of which (G4 and G5) contained the best lines for vegetative (G4) and productive (G5) characters