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BIOMECHANICAL DIFFERENCES IN THE STRAIGHTENING PROCESS AS EARLY SELECTION TRAIT OF STEM STRAIGHTNESS IN Pinus pinaster Ait.
Rosario Sierra de Grado
Last modified: 2009-06-26
Abstract
Rosario Sierra-de-Grado1, Valent'in Pando2, Pablo Mart'inez-Zurimendi1, Alejandro Pe~nalvo1, Esther B'ascones1, Bruno Moulia3.
1 Corresponding author
Departamento de Producci'on Vegetal y Recursos Forestales.
ETS Ingenier'ias Agrarias. Universidad de Valladolid.
Avda. de Madrid 44, 34004 Palencia. Tel (34) 979 108418. Fax: (34) 979108440
rsierra@pvs.uva.es
2Departamento de Estad'istica e Investigaci'on Operativa.
ETS Ingenier'ias Agrarias. Universidad de Valladolid.
Avda. de Madrid 44, 34004 Palencia.
3U.M.R. PIAF. INRA, Site de Crou"el
234 Avenue du Br'ezet. F-63039 Clermont-Ferrand cedex 02. Francia.
Abstract
Stem straightness is a major trait for Pinus pinaster Ait. breeding programs. Despite the stability of performance in provenance trials, the efficiency of breeding programs based on scoring stem forms remains low. An alternative approach for early selection is to analyse the biomechanical processes involved in the control of the stem form, instead of evaluating the form itself. The rationale is that genetic differences in the biomechanical ability to straighten in young plants will be active in controlling stem form lifelong. In this study, the components contributing most to the genetic differences between provenances in the straightening process were analyzed. To do so, a kinetic analysis and a biomechanical model that defines the non-linear interactions between the variables involved in the straightening process driven by secondary growth and reaction wood formation (Fournier's model) were used. This framework was tested on three P. pinaster provenances, selected for their differences in adult straightness and growth. One year-old plants were tilted 45o and individual stem position and size were recorded weekly during 5 months. The radial extension of reaction wood and the anatomical features of wood cells were measured on serial cross-sections. From this, the integral effect of reaction wood on stem leaning was computed using Fournier's model. Both primary and secondary-growth driven responses were involved in the straightening process of the plants, but the latter was more significant in the differences between provenances. Plants from the straight provenance showed higher ability in the straightening process due mainly to i) a more efficient compression wood (higher maturation strains) and ii) more pronounced secondary-growth driven autotropic decurving than the sinuous provenances. These two process-based traits are thus good candidates for early selection of stem straightness, as illustrated by their comparison with the more standard use of a quantitative flexuosity index of stem form. This new approach is nowadays being tested on a greater number of genotypes, as well the viability of the method with greater plants and in other species.
Key words: autotropism, biomechanics, breeding, differences between provenances, gravitropism, growth stress, maturation strains, reaction wood.
1 Corresponding author
Departamento de Producci'on Vegetal y Recursos Forestales.
ETS Ingenier'ias Agrarias. Universidad de Valladolid.
Avda. de Madrid 44, 34004 Palencia. Tel (34) 979 108418. Fax: (34) 979108440
rsierra@pvs.uva.es
2Departamento de Estad'istica e Investigaci'on Operativa.
ETS Ingenier'ias Agrarias. Universidad de Valladolid.
Avda. de Madrid 44, 34004 Palencia.
3U.M.R. PIAF. INRA, Site de Crou"el
234 Avenue du Br'ezet. F-63039 Clermont-Ferrand cedex 02. Francia.
Abstract
Stem straightness is a major trait for Pinus pinaster Ait. breeding programs. Despite the stability of performance in provenance trials, the efficiency of breeding programs based on scoring stem forms remains low. An alternative approach for early selection is to analyse the biomechanical processes involved in the control of the stem form, instead of evaluating the form itself. The rationale is that genetic differences in the biomechanical ability to straighten in young plants will be active in controlling stem form lifelong. In this study, the components contributing most to the genetic differences between provenances in the straightening process were analyzed. To do so, a kinetic analysis and a biomechanical model that defines the non-linear interactions between the variables involved in the straightening process driven by secondary growth and reaction wood formation (Fournier's model) were used. This framework was tested on three P. pinaster provenances, selected for their differences in adult straightness and growth. One year-old plants were tilted 45o and individual stem position and size were recorded weekly during 5 months. The radial extension of reaction wood and the anatomical features of wood cells were measured on serial cross-sections. From this, the integral effect of reaction wood on stem leaning was computed using Fournier's model. Both primary and secondary-growth driven responses were involved in the straightening process of the plants, but the latter was more significant in the differences between provenances. Plants from the straight provenance showed higher ability in the straightening process due mainly to i) a more efficient compression wood (higher maturation strains) and ii) more pronounced secondary-growth driven autotropic decurving than the sinuous provenances. These two process-based traits are thus good candidates for early selection of stem straightness, as illustrated by their comparison with the more standard use of a quantitative flexuosity index of stem form. This new approach is nowadays being tested on a greater number of genotypes, as well the viability of the method with greater plants and in other species.
Key words: autotropism, biomechanics, breeding, differences between provenances, gravitropism, growth stress, maturation strains, reaction wood.