© 2006 Heron Publishing—Victoria, Canada
Plasticity of growth and sylleptic branchiness in two poplar families grown at three sites across Europe
Nicolas Marron (1, 5), Catherine Bastien (2), Maurizio Sabatti (3), Gail Taylor (4) and Reinhart Ceulemans (1)
1. University of Antwerp, Department of Biology, Campus Drie Eiken, Research Group of Plant and Vegetation Ecology, Universiteitsplein
1, B-2610 Wilrijk, Belgium / 2. INRA, Unité Amélioration, Génétique et Physiologie Forestières, BP 20619, Ardon, 45166 Olivet Cedex, France / 3. Università degli Studi della Tuscia, Department of Forest Environment and Resources (DISAFRI), Via S. Camillo de Lellis, 01100
Viterbo, Italy / 4. University of Southampton, School of Biological Sciences, Bassett Crescent East, Southampton, SO16 7PX, U.K. / 5. Corresponding author (Nicolas.Marron@ua.ac.be) / Received May 31, 2005; accepted September 30, 2005; published online April 3, 2006
Summary
Two hybrid poplar maternal half-sib families, resulting from controlled crosses of the female parent Populus deltoides ‘S9-2’ with P. nigra ‘Ghoy’ and P. trichocarpa ‘V24’, were grown at three sites: northern Italy, central France and southern England. Juvenile stem growth traits (height,
circumference and volume) and sylleptic branchiness (number of branches, density of branches per unit of stem height, percentage
of the stem carrying branches and distance of the highest sylleptic branch to the top of the stem) were measured on 1-year-old
shoots. Our general objectives were to determine the degree to which the expression of stem growth and syllepsis and the relationships
between them are affected by environmental conditions and to evaluate the efficiency of indirect selection for stem growth
using branching traits as secondary criteria. The performance of both families differed significantly within and between sites.
Pronounced heterosis was observed and highly significant genotype × environment interactions were found for all traits across
the sites. Syllepsis showed more marked genetic variation and plasticity than stem growth traits. Relationships between sylleptic
branchiness and stem growth depended on environmental conditions. Heritability values at the individual level ranged between
0.09 and 0.59, but genetic gain in stem volume was not significantly improved when selection was based on sylleptic branch
characteristics. However, despite strong phenotypic plasticity among sites, genotypic ranking among the sites was relatively
stable.
Keywords:
genotype × environment interaction, heritability, heterosis, poplar.
