De la production de semences forestières.

International audienc

Fabre et Flahault se sont-ils trompés ? Plus d'un siècle après la création des arboretums de l'Aigoual, réflexions et discussions sur les leçons qui peuvent en être tirées.

Cet article est le compte rendu des rencontres organisées les 23 et 24 juillet 1998 par l'Association Camprieu-Nature, qui a bien voulu donner son accord pour publication. Il fait suite aux articles publiés dans la revue sur les arboretums (T. XIV, n°1, 1993) et sur les sapins (T. XIX, n°2, 1998

De la métapopulation au voisinage: la génétique des populations en déséquilibre

Tribune LibreInternational audienceThe concept of population is very useful but can sometimes lead to dead ends. Indeed, various questions in population genetics cannot be solved if studied at this level. It is shown that the intensity of dispersion, as far as it is genetically determined, does not respond to selection at the level of the population in its usual sens. A simple theorical model in relation with in-situ observations (on carduus), seems to show that a wider set, the matapopulation (Gill), is necessary to account for the processes concerned. From this viewpoint, instead of considering species as sets of independent populations, it is proposed to consider them as sets of metapopulations where individual populations are regulary founded by the others and then evolve under internal pressures. Are these internal pressures acting at the very population level ? It does not seem so, at least for some, and perhaps for most species, since each individual is likely to mate with a subset which is not representative of the whole. This question has led Wright to formulate the neighbourhood concept. In Thyme, the simultaneous integration of the emerging properties of the 3 levels (Metapopulation, Population and Neighbourhood) allows one to explain a phenomenon (very high proportions of females) which remained incomprehensible as long as one tried to describe it using only the population level

Grafting versus seed propagated apricot populations: two main gene pools in Tunisia evidenced by SSR markers and model-based Bayesian clustering

Apricot was introduced into the Mediterranean Basin from China and Asian mountains through the Middle-East and the Central Europe. Traditionally present in Tunisia, we were interested in accessing the origin of apricot species in the country, and in particular in the number and the location of its introductions. A set of 82 representative apricot accessions including 49 grafted cultivars and 33 seed propagated ‘Bargougs’ were genotyped using 24 microsatellite loci revealing a total of 135 alleles. The model-based Bayesian clustering analysis using both Structure and InStruct programs as well as the multivariate method revealed five distinct genetic clusters. The genetic differentiation among clusters showed that cluster 1, with only four cultivars, was the most differentiated from the four remaining genetic clusters, which constituted the largest part of the studied germplasm. According to their geographic origin, the five identified groups (north, centre, south, Gafsa oasis and other oases groups) enclosed a similar variation within group, with a low level of differentiation. Overall results highlighted the distinction of two apricot gene pools in Tunisia related to the different mode of propagation of the cultivars: grafted and seed propagated apricot, which enclosed a narrow genetic basis. Our findings support the assumption that grafting and seed propagated apricots shared the same origin

Mathematical Study of the Evolution of Gynodioecy with Cytoplasmic Inheritance under the Effect of a Nuclear Restorer Gene

A study is described of the influence of the introduction of a dominant nuclear restorer gene into a cytoplasmic gynodioecious plant population. This study includes the consideration of separate effects on the relative female fertility of nuclear, cytoplasmic and sex (phenotypic) factors. Under these assumptions, the introduction of a dominant nuclear restorer gene into a cytoplasmic gynodioecious population can lead to several different situations: persistence of cytoplasmic gynodioecy, appearance of a nuclear-cytoplasmic gynodioecy, appearance of a nuclear gynodioecy or complete restoration of male fertility. The development of stable nuclear-cytoplasmic gynodioecy in a mathematical model is new and is possible because of the consideration of the separate relative female fertilities. The possibility of a transformation of cytoplasmic gynodioecy into a nuclear one has never been obtained before. It could constitute a route for the appearance of this latter kind of gynodioecy in plant populations. Finally, the possibilities of evolution of gynodioecy from one kind to the other, and towards dioecy, are discussed, as are some theoretical schemes that seem to correspond to observed actual situations

The Bordeaux “Pont de Pierre” – A study case of micropiles reinforcement and benefits of HST method and Interaction Soil Structure design

International audienceThe "Pont de Pierre" of Bordeaux (France), built between 1810 and 1821, was, until 2014, the only link between the two borders of the Garonne River. Today, it is a strategical axis that is used every day by 100 000 passengers (on foot, by bicycle or by tram). Since its construction, the bridge has been affected by significant settlement. In 1992-1994 and 2002-2003, 16 micropiles drilled into the masonry of each pillar reinforced the first six pillars. A detailed monitoring analysis (before and after reinforcement) is undertaken to expose the effects of micropile reinforcement and the load transfer process. In addition, an analysis of tidal effects is also carried out. Then, a soilstructure interaction model and a soil-pile-soil model are developed and fitted to the previous analysis. The results are compared with the reinforcement design obtained by the safety factor approach. The importance of considering the relative stiffness between micropiles and timber piles to improve the design of reinforcements (micropiles) is highlighted. The analysis sheds light on the issue of strengthening the last 11 pillars projected for 2023-2025