The Guiana cacao genetic group (Theobroma cacao L.): a new core collection in French Guiana

International audienceSince 1985, CIRAD has been involved in surveying, collecting, studying and conserving ex situ wild cacao trees of French Guiana. Around 225 accessions of this genetic material (open progenies and clones), derived from 18 demes (sub-populations), are currently conserved in a collection at the Perennial Plants Biological Resource Centre (CRB-PPG) in French Guiana, at CIRAD's Paracou-Combi station, in Sinnamary. In 2004, an initial "core collection" of clones was founded on a virtually exhaustive representation of the different demes collected, with some phenotypically well-described clones. Following the genotyping of 181 of those clones by GBS (Genotyping by Sequencing), the availability of a large number of SNP markers (Single Nucleotide Polymorphism) enabled us to modernize the "core collection". Thus, of the 181 wild cacao trees clones, genotyped by 1953 SNPs (without missing data), a new core collection was obtained using COREFINDER software, comprising 41 clones representing 100% of the variability encountered

Role of ascospores and conidia in the initiation and spread of South American leaf blight in a rubber tree plantation

International audienceMicrocyclus ulei, the fungus causing South American leaf blight (SALB) on rubber tree leaves, produces two main types of spores: ascospores and conidia. To assess their respective epidemiological role, a field experiment was conducted in French Guiana over 3years. Tree phenology, disease severity and climate variables were recorded while airborne spores were trapped and quantified. Ascospores were shown to play an essential role in the perpetuation of the disease outside the host's growth periods, in the resumption of epidemics, and in the spread of the disease to disease-free zones. Conidia were trapped in visibly infected plots only, during periods of host growth. Disseminated over short distances and present only temporarily on leaves, the conidia enabled the disease to spread stepwise when the climate was conducive. Segmentation analysis revealed that the duration of high relative humidity was the climatic variable most related to ascospore trapping. Ascospore release did not require low temperatures. Considering the essential role of the ascospores in the initiation and spread of disease, artificial defoliation as a means of reducing the inoculum pressure during tree refoliation is proposed to control SALB. To check the validity of this method, a survey over several years of natural defoliation-refoliation in relation to climate and other leaf diseases is needed

Pioglitazone induces in vivo adipocyte differentiation in the obese Zucker fa/fa rat

Thiazolidinediones are potent antidiabetic compounds, in both animal and human models, which act by enhancing peripheral sensitivity to insulin. Thiazolidinediones are high-affinity ligands for peroxisome proliferator-activated receptor-gamma, a key factor for adipocyte differentiation, and they are efficient promoters of adipocyte differentiation in vitro. Thus, it could be questioned whether a thiazolidinedione therapy aimed at improving insulin sensitivity would promote the recruitment of new adipocytes in vivo. To address this problem, we have studied the in vivo effect of pioglitazone on glucose metabolism and gene expression in the adipose tissue of an animal model of obesity with insulin resistance, the obese Zucker (fa/fa) rat. Pioglitazone markedly improves insulin action in the obese Zucker (fa/fa) rat, but doubles its weight gain after 4 weeks of treatment. The drug induces a large increase of glucose utilization in adipose tissue, where it stimulates the expression of genes involved in lipid metabolism such as the insulin-responsive GLUT, fatty acid synthase, and phosphoenolpyruvate carboxykinase genes, but decreases the expression of the ob gene. These changes are related to both an enhanced adipocyte differentiation, as shown by the large increase in the number of small adipocytes in the retroperitoneal fat pad, and a direct effect of pioglitazone on specific gene expression (phosphoenolpyruvate carboxykinase and ob genes) in mature adipocytes

Instabilités induites par la dissipation dans les structures couplées à un écoulement

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