Etude de la biologie d'une messicole en régression : le bleuet (Centaurea cyanus L.)

Abstract : Agroecosystems are currently experiencing high biodiversity loss, in particular among the plant species specifically adapted to this habitat. This decline results from cropping systems that have been intensified in Western Europe since the 1950s. The cornflower (Centaurea cyanus L.), considered as emblem of the flora associated with traditional cereals, appears as a species that may be at risk and should be monitored. Indeed, cornflower can serve as a host to predators of crop pests and is strongly attractive for the pollinators. This study examines the biological factors that could potentially cause the decline of this species: spatial distribution, potential for growth, population's genetic diversity, seeds survival and mating system.We have shown that C. cyanus is not a biological indicator of the weed diversity of a field. However, when it is not frequent in a region, cornflower is associated with other rare segetal species. When it is common in a region, C. cyanus is present in areas with higher weed diversity. Sowing seeds in different components of the agrosystem, without herbicide application, shows that the growth of cornflower was higher in the centre of a wheat field than in mustard and the crop edge. Growth success in field margins was variably limited according to the weed communities in the field boundaries. The analysis of the genetic diversity using microarrays has shown that populations in a small agricultural area are connected by important genes flow. The ecological barriers as country road seem to be factors more determinant than geographical distance to structure and divide populations. Therefore, the cornflower distribution in the agricultural landscape is not random and appears to be linked to species frequency in the area and to landscape elements.The cornflower life cycle characteristics were studied through field and greenhouse experiments. We have shown that the longevity of achenes buried in the soil falls rapidly after two years. There is a seasonal dormancy cycle that allows the emergence of two seedling cohorts (fall and spring). Our study of the mating system highlights the fact that pollinators are required for fertilization and that cornflower is strongly self-incompatible. However, there are pseudo self-incompatible individuals, but their frequency is not related to the population size or the spatial isolation level. Individual fitness decreases as the inbreeding coefficient increases in a population. Inbreeding depression is mainly expressed during the germination stage. All these biological characteristics can be detrimental to the cornflower in current simplified agroecosystems and may have led to cornflower decline in some areas
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Solène Bellanger. Etude de la biologie d'une messicole en régression : le bleuet (Centaurea cyanus L.). Biologie végétale. Université de Bourgogne, 2011. Français. ⟨NNT : 2011DIJOS087⟩. ⟨tel-00741148⟩

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