Biomechanical differences in the stem straightening process among Pinus pinaster provenances. A new approach for early selection of stem straightness
Rosario Sierra-de-Grado (1, 2), Valentín Pando (3), Pablo Martínez-Zurimendi (1), Alejandro Peñalvo (1), Esther Báscones (1) and Bruno Moulia (4)
1. Departamento de Producción Vegetal y Recursos Forestales, ETS Ingenierías Agrarias, Universidad de Valladolid, Avda. de Madrid
44, 34004 Palencia, Spain / 2. Corresponding author () / 3. Departamento de Estadística e Investigación Operativa, ETS Ingenierías Agrarias, Universidad de Valladolid, Avda. de Madrid
44, 34004 Palencia, Spain / 4. UMR PIAF, INRA, Site de Crouël, 234 Avenue du Brézet, F-63039 Clermont-Ferrand Cedex 02, France / Received July 13, 2007; accepted October 23, 2007; published online April 1, 2008
Summary
Stem straightness is an important selection trait in Pinus pinaster Ait. breeding programs. Despite the stability of stem straightness rankings in provenance trials, the efficiency of breeding
programs based on a quantitative index of stem straightness remains low. An alternative approach is to analyze biomechanical
processes that underlie stem form. The rationale for this selection method is that genetic differences in the biomechanical
processes that maintain stem straightness in young plants will continue to control stem form throughout the life of the tree.
We analyzed the components contributing most to genetic differences among provenances in stem straightening processes by kinetic
analysis and with a biomechanical model defining the interactions between the variables involved (Fournier’s model). This
framework was tested on three P. pinaster provenances differing in adult stem straightness and growth. One-year-old plants were tilted at 45°, and individual stem
positions and sizes were recorded weekly for 5 months. We measured the radial extension of reaction wood and the anatomical
features of wood cells in serial stem cross sections. The integral effect of reaction wood on stem leaning was computed with
Fournier’s model. Responses driven by both primary and secondary growth were involved in the stem straightening process, but
secondary-growth-driven responses accounted for most differences among provenances. Plants from the straight-stemmed provenance
showed a greater capacity for stem straightening than plants from the sinuous provenances mainly because of (1) more efficient
reaction wood (higher maturation strains) and (2) more pronounced secondary-growth-driven autotropic decurving. These two
process-based traits are thus good candidates for early selection of stem straightness, but additional tests on a greater
number of genotypes over a longer period are required.
