" Soutenance de thèse de Alexandre MARCHAL. | Université d'Orléans

Université d'Orléans

Soutenance de thèse de Alexandre MARCHAL.

30/01/2018 - 14:00 - 30/01/2018 - 18:00

URL: http://www.univ-orleans.fr/actus/soutenances

Nom du contact: Etudes Doctorales

Courriel du contact: etudes.doctorales@univ-orleans.fr

Lieu: Amphithéâtre - Bâtiment Recherche - 5 rue de Carbone - campus UNIVERSITÉ

Titre : Larch hybrid vigor and role of the phenotypic plasticity in the construction of heterosis.

Discipline : Biologie

ECOLE DOCTORALE SSBCV

Résumé :

European larch (Larix decidua) has been historically exploited within its natural range for its high quality wood, but the attempt to grow this species outside its native range was a failure. Hybridization with Japanese larch (L. kaempferi) is a promising path, in particular because of the heterosis this hybrid manifests. In this dissertation, we took advantage of an old-enough, multi-site experiment with an inter-/intra-specific mating design. The first chapter presents the analysis of several traits involved in wood quality and productivity. We confirmed heterosis for volume related traits. The heterosis came with no counterpart in wood quality, and it was stable across sites. Contrarily, some other traits showed no heterosis but higher heritabilities, and the additive performances for these traits were stable across sites and in pure species vs. in hybridization. In the second chapter, we investigated the role of phenotypic plasticity of some wood formation traits in the construction of the heterosis. Hybrid larch appeared as the most plastic taxon: it equaled the parental controls in producing narrow growth increments under drought, but it produced the largest rings in favorable water availability conditions. This second chapter was also a first step towards a better understanding of the role of phenotypic plasticity on the construction of the genetic variance architecture between larch stem circumference and density. The dissertation ends with a synthesis in which we discussed the implication of our findings for the breeding of hybrid larch.