Phenotypic variation of basic wood density in Pinus ponderosa plus trees

Abstract

SUMMARYPhenotypic selection generally reduces the variability of both the selected trait and other associated characteristics. Some species show a negative strong relationship between growth traits and wood density. In the present study, basic wood density was assessed in a group of 23 control trees and 25 Pinus ponderosa plus trees, selected for growth and form traits in the Argentine Patagonia region. Trees were sampled in four different sites from the environmental and silvicultural point of view. We aim to study if the phenotypic variation in wood density is somehow influenced by the selection for productivity and form. The average wood density of plus trees was 0.37 g cm -3 , ranging from 0.29 to 0.46 g cm -3 . These values were not significantly different to control trees and were similar to those previously found in P. ponderosa plantations growing in the region. Wood density of the improved population, represented by plus trees did not differ from that of base population from which plus trees were selected. Significant differences were found in wood basic density among sites and age-classes. The phenotypic variation of the increment of wood density from pith to bark and among trees was different from zero. Not significant association was found between wood basic density and growth and form traits, except for stem straightness. It would be possible to identify high wood density trees at half of the rotation age.Key words: specific wood density, repeated measurements, genetic breeding, Patagonian, Argentine. RESUMENLa selección fenotípica generalmente reduce la variabilidad de los caracteres seleccionados y la de los caracteres asociados. Algunas especies muestran asociación negativa entre crecimiento y densidad de la madera. En este estudio, se evaluó la densidad básica de la madera en un grupo de 23 árboles control y 25 árboles plus de Pinus ponderosa seleccionados por criterios de crecimiento y forma en la región norpatagónica de Argentina. Las muestras provinieron de cuatro sitios con diferente clima y silvicultura. El objetivo fue determinar si la variación fenotípica de la densidad de la madera pudo haber sido afectada por la selección para productividad y forma. La densidad media de la madera de los arboles plus fue de 0,37 g cm -3 , variando desde 0,29 hasta 0,46 g cm -3 . Estos valores no fueron significativamente diferentes a los registrados en los árboles control y similares a los previamente registrados para P. ponderosa creciendo en la región. La densidad de la madera de la población de mejora (árboles plus) no difirió de la población base donde fue seleccionada. Diferencias significativas para la densidad de la madera se pudieron establecer entre sitios y clases de edad. El incremento de la densidad desde la médula hacia la corteza y la variación fenotípica entre árboles fue significativamente diferente de cero. La densidad no se encontró asociada a las características de crecimiento y forma, por las cuales los árboles plus fueron seleccionados, excepto con la rectitud de fuste. Sería posible...

Micro-evolutionary patterns of juvenile wood density in a pine species

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