engleski

Genetic structure and variability of phenological forms of pedunculate oak (Quercus Robur L.)from clonal seed orchards in Croatia

Mass selection of pedunculate oak (Quercus robur L.) in Croatia started in the 1980s and 150 plus trees were selected within three breeding zones. Three clonal seed orchards (CSOs) were established with grafted plus-trees. A clonal trial was planted with ramets from the majority of those trees and significant differences in flushing phenology were observed between the clones, with 20 days difference between the earliest and latest flusher. Bud breaking is an adaptive trait under strong genetic control. Variation in flushing phenology is presumably one of the species’ defensive strategies against late frosts. There are some reports of significant differences in genetic variability and differentiation among phenoforms within temperate tree species, e.g. late-flushing forms of European beech had a higher intrapopulation genetic variability than early-flushing forms. The aim of this study was to compare variability within and among CSOs and investigate the genetic structure of clone phenoforms from the CSOs. Flushing phenology was assesed on a 1–7 scale (1 - dormant buds ; 7 - fully developed leaves). Flushing phenoforms were determined based on clones’ flushing stage on 18 April 2008. Genetic variability and structure were analysed at eight polymorphic SSR loci. Total number of alleles per locus (Na), observed (Ho) and expected (He) heterozygosity and PIC for each locus, average number of alleles (Navg), Ho and He, allelic richness (Nar) and number of private alleles (Npr) in each CSO and each phenoform were calculated. Nar, Ho and He among CSOs and among phenoforms were compared using the Kruskal-Wallis test. Genetic differentiation among CSOs was estimated by FST. The distance matrix for the proportion of shared alleles was subjected to AMOVA to partition total SSR diversity into among and within CSOs and phenoforms. Both CSOs and phenoforms were not significantly different for Na, Ho and He, and there were no significant differences in genetic differentiation among phenoforms. It seems that neutral markers analysed were not associated with adaptive differences between phenoforms. Additionally, the results indicate the absence of genetic differentiation between the breeding zones which raises an argument for the reconsideration of their existing delineation in Croatia.

genetic differentiation; microsatellites; oak; plus trees; selection

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