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NFM, Volume 39: 35–45.
Original scientific paper

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Abstract

Pedunculate oak is one of the three most common tree species in Croatia and has an important role in economic, social and environmental terms. Knowledge of the genetic structure for such a significant forest tree species is the fundamental prerequisite for its future preservation. Specifically, the knowledge of the genetic structure allows more advanced use of forest reproductive material in order to increase the adaptability of oak populations to stressful environmental conditions. Analysis of quantitative (polygene, metric) phenotypic traits in genetic field trials is one of the methods to determine forest tree species genetic structure. Seed material was collected from sixteen seeds and one normally managed stand, representing the distribution range of pedunculate oak in Croatia, in September and October 2006. With two-year-old seedlings, in 2008 a genetic field trial was established in the area of the Management Unit Jastrebarski lugovi. The height growth was measured and the survival and height increment were determined through three consecutive years (2010–2012). The variance analysis was performed by the PROC MIXED procedure in the SAS statistical package, and the variance components and the statistical significance of random effects were calculated (blocks, populations, population within populations, interactions of block with populations, and interaction of blocks with families with populations). Variance components were used to calculate the QST parameter that determines the level of interpopulation genetic differentiation. Multivariate regression tree analysis (MRT) was used to determine the pattern of genetic differentiation and classify population into groups (clusters) for the investigated quantitative traits, depending on the environmental (climatic) variables of their habitat of origin. The QST parameter was high for all three analysed traits, which clearly indicates interpopulation genetic differentiation of Croatian oak populations. The established pattern of adaptive genetic differentiation is confirmed by the ecotypic pattern, i.e. most probably the natural selection in parental stands (primarily considering the humidity and heat of the habitat) caused the genetic differentiation of local populations.

Keywords: genetic structure, quantitative phenotypic traits, genetic field trial, ecotypic variability, natural selection