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Des analyses dendro-anthracologiques ont été réalisées sur 19 sites archéologiques qui se concentrent en plaine de Limagne et se répartissent du cinquième millénaire av. J.-C. au iiie siècle ap. J.-C. Elles concernent différentes structures de combustion, structures en creux et structures d’habitat. Ces données indiquent un changement dans l’approvisionnement en bois entre le premier et le second Âge du Fer : le hêtre devient alors majoritaire devant le chêne. Sur la base des données polliniques, cette évolution ne semble pas être en relation avec un changement dans la disponibilité du bois localement, la hêtraie étant déjà existante dans la région depuis l’Âge du Bronze. La diversité en taxons héliophiles croissante au cours du temps, l’augmentation des largeurs moyennes de cernes des charbons de chêne caducifolié, ainsi qu’une multiplication des sites ayant livré plus de 10 % de bois de petit calibre (branches, brindilles), révèlent un peuplement végétal de plus en plus hétérogène, ouvert et la mise en place d’une végétation basse de reconquête. Cette évolution du couvert végétal est synchrone d’une intensification de l’occupation des sols en constante progression jusqu’à l’Empire romain durant lequel le réseau parcellaire et de villae est très dense en Basse Auvergne. Les analyses anthracologiques présentées ici sont une succession de cas particuliers qui réunis et interprétés ensemble permettent d’esquisser une histoire de la gestion de la ressource en bois du Néolithique à la conquête romaine. Dendro-anthracological analyses were performed on 19 archaeological sites located in the Limagne plain and dated from the 5th millennium BC to the 3rd century AD. Analyses concerned different archaeological contexts such as fireplaces, post-holes and settlement sites. The data shows a change in wood supply with time, namely the replacement of oak by beech between the 1st and the 2nd Iron Age. On the light of pollen records, this change does not seem to be related to a contemporary change in local wood availability as beech forests were already present in the area from the Bronze Age. Besides, the higher diversity of heliophilous taxa, the increasing trend of the oak fc. charcoal average tree ring width and the proliferation of sites reporting more than 10 % of small coals - i.e. branches, twigs - reveal a heterogeneous vegetation context which included a low undergrowth cover like as hedges and thickets. Such environmental diversification reported from the early Iron Age, which is further stressed from the second Iron Age, corroborates the land use pattern documented in the Basse Auvergne from this age to the Roman period. This shows a progressively denser settlement with a land plot network and villae. Anthracological analyses presented in this article are a series of particular case-studies which interpreted all together enable us to define the timber resource management history of the Basse Auvergne from the Neolithic to the Roman period.

Ustilago scitaminea Sydow, which causes sugarcane smut disease, has been spreading throughout Africa and America since the 1950s. The objectives of the present study were (1) to confirm and further describe the global population structure of U. scitaminea on the basis of a larger number of isolates and (2) to infer its reproduction system. Microsatellite markers, that present the advantage of being highly polymorphic, PCR-based, reproducible and codominant, were therefore developed for U. scitaminea and used to analyse a sample of single-teliospore isolates from various sugarcane-producing countries around the world. We surveyed 142 single-spore isolates of Ustilago scitaminea for genetic diversity. The fungal samples were teliospores from 77 single whips (sori) collected on various cultivars and at different locations in 15 sugarcane-growing countries throughout the world. The overall genetic structure of this fungus was investigated using 17 polymorphic microsattelite loci. All isolates but one were homozygous for all loci, indicating that selfing could be the highly preferential predominant reproductive mode of U. scitaminea. In America and Africa, genetic diversity was found to be extremely low and all isolates belonged to a single inbred lineage. This inbred lineage was also found in some parts of the Asian continent where most U. scitaminea genetic diversity was detected. These observations support the hypothesis that the fungus originated in Asia. The strong founder effect observed in the global genetic structure of U. scitaminea suggests that the fungus migrated from Asia to other continents on rare occasions. (Texte intégral)