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Okra has significant area under cultivation in Africa and Asia, despite it has been considered as a minor crop and not much attention has been given to okra improvement in international research program. Niger produced during 2008, 2794 t of okra in 5288 ha with mean productivity of 0.39 t.ha-1. This poor average productivity is far below than the mean productivity of East Africa (6.2 t.ha-1) and North (8.8 t.ha-1). Non-availability of varieties resistant to local biotic stresses is one of the major reasons for such a low productivity. Root-knot nematode disease is one of the constraints of commercial okra cultivation in region and cause of poor productivity. Durable host plant resistance/tolerance is considered as better option than the management tactic solely based on insecticide spray alone. The major objective of this study initited by AVRDC is to screening okra germplasm against root knot nematode in order to identify resistant lines. A total of 48 lines belonging to two species (A. esculentus and A. caillei) originated from different countries were screened following the protocol developed during this study. The results showed that after five weeks of inoculation, infestation of nematode is very fatal for susceptible okra genotypes. Cluster analysis using various parameters revealed that groups GI, GV and GII represented lines which are showing less gall index and poor reproduction rate of nematode, whereas GIII and GIV represented lines with more gall index with higher reproduction rate. The lines showing reaction towards resistance can be used in the breeding program. Key words: Abelmoschus species, okra germplasm, Meloidogyne species, root knot, nematode, screening.

International audience

International audience; Phenotypic changes in plants can be observed along many environmental gradients and are determined by both environmental and genetic factors. The identification of alleles associated with phenotypic variations is a rapidly developing area of research.We studied the genetic basis of phenotypic variations in 11 populations of wild pearl millet (Pennisetum glaucum) on two NorthSouth aridity gradients, one in Niger and one in Mali. Most of the 11 phenotypic traits assessed in a common garden experimentvaried between the populations studied. Moreover, the size of the inflorescence, the number of flowers and aboveground dry mass co-varied positively with a decrease in rainfall. To decipher the genetic basis of these phenotypes, we used an associationmapping strategy with a mixed model. We found two SNPs on the same myosin XI contig significantly associated with variations in the average number of flowers. Both the allele frequency of the two SNPs and the average number of flowers co-varied withthe rainfall gradient on the two gradients. Interestingly, this gene was also a target of selection during domestication. The Myosin XI gene is thus a good candidate for fitness-related adaptation in wild populations.

International audience; Several studies suggestthat cis-regulatory mutations are the favorite target of evolutionary changes, one reason being that cis-regulatory mutations might have fewer deleterious pleiotropic effects than protein-coding mutations. A review of the process also suggests that this bias towards adaptive cis-regulatory variation might be less pronounced at the intraspecific level compared with the interspecific level. In this study, we assessed the contribution of cis-regulatory variation to adaptation at the intraspecific level using populations of wild pearl millet (Cenchrus americanus ssp. monodii) sampled along an environmental gradient in Niger. From RNA sequencing of hybrids to assess allele-specific expression, we identified genes with cis-regulatory divergence between two parental accessions collected in contrasted environmental conditions. This revealed that similar to 15% of transcribed genes showed cis-regulatory variation. Intersecting the gene set exhibiting cis-regulatory variation with the gene set identified as targets of selection revealed no excess of cis-acting mutations among the selected genes. We additionally found no excess of cis-regulatory variation among genes associated with adaptive traits. As our approach relied on methods identifying mainly genes submitted to strong selection pressure or with high phenotypic effect, the contribution of cis-regulatory changes to soft selection or polygenic adaptive traits remains to be tested. However our results favor the hypothesis that enrichment of adaptive cis-regulatory divergence builds up over time. For short evolutionary time-scales, cis-acting mutations are not predominantly involved in adaptive evolution associated with strong selective signal.

Uncovering genomic regions involved in adaption is a major goal in evolutionary biology. High-throughput sequencing now makes it possible to tackle this challenge in nonmodel species. Yet, despite the increasing number of methods targeted to specifically detect genomic footprints of selection, the complex demography of natural populations often causes high rates of false positive in gene discoveries. The aim of this study was to identify climate adaptations in wild pearl millet populations, Cenchrus americanus ssp. monodii. We focused on two climate gradients, one in Mali and one in Niger. We used a two-step strategy to limit false-positive outliers. First, we considered gradients as biological replicates and performed RNA sequencing of four populations at the extremities. We combined four methods-three based on differentiation among populations and one based on diversity patterns within populations-to identify outlier SNPs from a set of 87 218 high-quality SNPs. Among 11 155 contigs of pearl millet reference transcriptome, 540 exhibited selection signals as evidenced by at least one of the four methods. In a second step, we genotyped 762 samples in 11 additional populations distributed along the gradients using SNPs from the detected contigs and random SNPs as control. We further assessed selection on this large data set using a differentiation-based method and a method based on correlations with environmental variables based. Four contigs displayed consistent signatures between the four extreme and 11 additional populations, two of which were linked to abiotic and biotic stress responses.