Phoma du tournesol : déterminisme de la tolérance de l'hôte à la maladie

La maladie des taches noires du tournesol, dont l'agent responsable est le champignon Phoma macdonaldii, n'a jusqu'alors été que très peu étudiée. En France, si son apparition remonte au début des années 1980, elle provoque aujourd'hui des dégâts de plus en plus inquiétants. Elle a été classée, en 2004, deuxième maladie plus importante après le Mildiou, par les acteurs de la filière tournesol. Aucun génotype de tournesol n'a pu à ce jour être répertorié comme résistant à la maladie ; nous ne disposons que de génotypes tolérants. Nos travaux, qui se sont orientés selon trois axes, ont permis de mettre en évidence différents points : - Une étude histologique a révélé que le premier frein à la pénétration du champignon dans les cellules de l'hôte semble être des ornementations cuticulaires particulières plus prononcées chez le génotype tolérant par rapport au génotype sensible. Une cinétique de l'infection a également été réalisée. - L'étude des phytoalexines du tournesol, la scopolétine et l'ayapine, a permis de mettre en évidence que ces dérivés coumariniques ont un effet inhibiteur important sur la germination du champignon, et que l'ayapine est également capable d'inhiber la croissance de Phoma macdonaldii. De plus, le dosage de la scopolétine in planta, à différents temps après contamination par le Phoma, a prouvé que la molécule présentait un niveau de synthèse et d'accumulation jusqu'à deux fois plus élevé chez le génotype tolérant étudié par rapport au génotype sensible. - Enfin, grâce à la mise au point d'une puce à ADN composée de 1000 unigènes, dont plus de 100 gènes impliqués dans la résistance des plantes aux maladies, nous avons pu mettre en exergue l'expression différentielle de certains gènes entre un génotype tolérant et génotype sensible, en réponse à l'infection. Ces gènes pourraient être impliqués dans la tolérance du tournesol à Phoma macdonaldii. Les différents résultats obtenus nous laissent envisager une amélioration du tournesol afin d'augmenter son niveau de résistance aux maladies

Effects of genotype and sowing date on phytostanol-phytosterol content and agronomic traits in wheat under organic agriculture

Cereals are an important source of sterols and stanols in the human diet. The present study underlines the effect of genotype and weather conditions in bread wheat, on total sterol and stanol content (TSS), agronomic traits, proteins and ash content under organic conditions. Variations in TSS as well as other characters between two sowing dates were observed. A broad genotypic variability was also reported since extreme genotypes differed by more than 30 mg 100. g-1 DW for TSS, with total stanol content varying twofold. Moreover, two groups of genotypes that differed in agronomic production, ash and protein content were depicted, based on their response to an increase in temperature. This result suggests that the genotypic factor prevails over the sowing date factor for determining sterol and stanol traits in wheat cultivated under organic conditions. Nevertheless, a strong interaction exists between the two factors, which can be used to drive bioaccumulation of these molecules

Sterol concentration and distribution in sunflower seeds (Helianthus annuus L.) during seed development

Sunflower seeds are currently used for edible oil production. Among oil minor compounds, phytosterols are of special interest due to their cholesterol reducing properties. This paper reports studies on their accumulation and distribution in the embryo and hull, and the effects of temperature on phytosterol contents in sunflower seed produced under both conventional and organic field conditions. An optimized method of sterol determination, adapted to studies on small samples of seed, is presented. Seventy-two % of phytosterols were found in the embryo, 28 % in the hull. The periods of phytosterols concentration varied according to sterol category and seed part. Application of these results to improve production of natural sterols for functional food use is discussed

Sterol content in sunflower seeds (Helianthus annuus L.) as affected by genotypes and environmental conditions

Phytosterols play essential roles in many plant cell mechanisms. They are of industrial interest since, as part of the diet, they can reduce Low Density Lipoprotein cholesterol. An increase in plant sterol contents by improved crop varieties or crop management could help to answer industrial demands and also to develop environmentally friendly extraction methods. The aim of this study was to evaluate genotypic variability for sterol content in cultivated sunflower and effects of sowing date, in particular sowing date. Results showed large variability among a collection of sixteen sunflower inbred lines and hybrids. Total sterols varied almost twofold between extreme genotypes. A delay of sowing, giving higher temperatures during seed formation, induced a general increase in total sterol concentration by up to 35 per cent, as well as sterol composition but this varied according to genotype. These results are discussed with the aim of improving sterol content by sunflower breeding programmes

Response surface methodology to optimise Accelerated Solvent Extraction of steviol glycosides from Stevia rebaudiana Bertoni leaves

Following the approval of steviol glycosides as a food additive in Europe in December 2011, large-scale stevia cultivation will have to be developed within the EU. Thus there is a need to increase the efficiency of stevia evaluation through germplasm enhancement and agronomic improvement programs. To address the need for faster and reproducible sample throughput, conditions for automated extraction of dried stevia leaves using Accelerated Solvent Extraction were optimised. A response surface methodology was used to investigate the influence of three factors: extraction temperature, static time and cycle number on the stevioside and rebaudioside A extraction yields. The model showed that all the factors had an individual influence on the yield. Optimum extraction conditions were set at 100°C, 4min and 1 cycle, which yielded 91.8%±3.4% of total extractable steviol glycosides analysed. An additional optimisation was achieved by reducing the grind size of the leaves giving a final yield of 100.8%±3.3%

A cDNA microarray approach to decipher sunflower (Helianthus annuus) responses to the necrotrophic fungus Phoma macdonaldii

To identify the genes involved in the partial resistance of sunflower (Helianthus annuus) to the necrotrophic fungus Phoma macdonaldii, we developed a 1000‐element cDNA microarray containing carefully chosen genes putatively involved in primary metabolic pathways, signal transduction and biotic stress responses. A two‐pass general linear model was used to normalize the data and then to detect differentially expressed genes. This method allowed us to identify 38 genes differentially expressed among genotypes, treatments and times, mainly belonging to plant defense, signaling pathways and amino acid metabolism. Based on a set of genes whose differential expression was highly significant, we propose a model in which negative regulation of a dual‐specificity MAPK phosphatase could be implicated in sunflower defense mechanisms against the pathogen. The resulting activation of the MAP kinase cascade could subsequently trigger defense responses (e.g. thaumatin biosynthesis and phenylalanine ammonia lyase activation), under the control of transcription factors belonging to MYB and WRKY families. Concurrently, the activation of protein phosphatase 2A (PP2A), which is implicated in cell death inhibition, could limit pathogen development. The results reported here provide a valuable first step towards the understanding and analysis of the P. macdonaldii–sunflower interaction

Ethylene stimulates growth and affects fatty acid content of Synechocystis sp. PCC 6803

This set of results shows that the growth of wild type Synechocystis sp. PCC 6803 was enhanced by exogenous ethylene and inhibited by 1-methylcyclopropene (1-MCP), a specific inhibitor of ethylene receptors. The fact that the growth of a Synechocystis sp. PCC 6803 strain with the ethylene receptor deleted was unaffected by exogenous ethylene, brings additional proof that this is a specific effect of ethylene. The results also confirm previous observations regarding the positive impact of ethylene on the photochemical efficiency of PSII. Additionally, it was observed that exogenous ethylene enhanced accumulation of C16:0 and C18:0 and C18:1 in the wild type strain. Finally, observations were performed regarding the capacity of the wild type strain to biosynthesize ethylene in the culture medium in the presence of methionine. These results and the recent description of an ethylene receptor in Synechocystis should lead to new areas of research in the field of microalgae

Phoma du tournesol (déterminisme de la tolérance de l'hôte à la maladie)

La maladie des taches noires du tournesol, dont l'agent responsable est le champignon Phoma macdonaldii, n'a jusqu'alors été que très peu étudiée. En France, si son apparition remonte au début des années 1980, elle provoque aujourd'hui des dégâts de plus en plus inquiétants. Elle a été classée, en 2004, deuxième maladie plus importante après le Mildiou, par les acteurs de la filière tournesol. Aucun génotype de tournesol n'a pu à ce jour être répertorié comme résistant à la maladie ; nous ne disposons que de génotypes tolérants. Nos travaux, qui se sont orientés selon trois axes, ont permis de mettre en évidence différents points : - Une étude histologique a révélé que le premier frein à la pénétration du champignon dans les cellules de l'hôte semble être des ornementations cuticulaires particulières plus prononcées chez le génotype tolérant par rapport au génotype sensible. Une cinétique de l'infection a également été réalisée. - L'étude des phytoalexines du tournesol, la scopolétine et l'ayapine, a permis de mettre en évidence que ces dérivés coumariniques ont un effet inhibiteur important sur la germination du champignon, et que l'ayapine est également capable d'inhiber la croissance de Phoma macdonaldii. De plus, le dosage de la scopolétine in planta, à différents temps après contamination par le Phoma, a prouvé que la molécule présentait un niveau de synthèse et d'accumulation jusqu'à deux fois plus élevé chez le génotype tolérant étudié par rapport au génotype sensible. - Enfin, grâce à la mise au point d'une puce à ADN composée de 1000 unigènes, dont plus de 100 gènes impliqués dans la résistance des plantes aux maladies, nous avons pu mettre en exergue l'expression différentielle de certains gènes entre un génotype tolérant et génotype sensible, en réponse à l'infection. Ces gènes pourraient être impliqués dans la tolérance du tournesol à Phoma macdonaldii. Les différents résultats obtenus nous laissent envisager une amélioration du tournesol afin d'augmenter son niveau de résistance aux maladies.TOULOUSE-ENSAT-Documentation (315552324) / SudocSudocFranceF

Selection of Italian cardoon genotypes as industrial crop for biomass and polyphenol production

International audienceEight cardoon genotypes, of which seven Italian cultivated and one wild cardoon, belonging to the ENEA-Tuscia University joint collection, were assessed over two growing seasons with the aim of evaluating biomass production for pharmaceutical uses. Nine morphological descriptors (plant height and diameter, number of lateral shoots, main flower stem diameter, first fully developed leaf length and width, number of leaf lobes, plant fresh and dry weight) were selected to describe plant vigor and dry matter accumulation. Biochemical characterization of aboveground biomass was also undertaken, using accelerated solvent extraction (ASE) and HPLC analyses. Significant differences among genotypes were found for many of the agro-morphological traits evaluated. In particular, results identified aerial biomass yield, which ranged between 1095 and 2495 g plant−1, as a useful trait in discriminating among genotypes. Significant differences among genotypes were also found for biomass polyphenol content. The most representative compounds detected were caffeoylquinic acids (3-O-caffeoylquinic acid and 1,5-O-dicaffeoylquinic acid) and flavonoid derivatives (cynaroside). The 3-O-caffeoylquinic acid content in biomass extracts ranged from 0.01 to 2.65 g kg−1 DM, while the 1,5-O-dicaffeoylquinic acid varied from 3.08 to 4.07 g kg−1 DM. With regard to cynaroside, the cultivated cardoon “AFN” showed the highest value (4.20 g kg−1 DM). Taking into account that the analyzed germplasm has never been selected for biomass or polyphenol compound production, our data highlight the potential use of cardoon genotypes for biomass and pharmaceutical purposes