Genetic Diversity of Pedunculate Oak (Quercus robur L.) in Clonal Seed Orchards in Croatia, Assessed by Nuclear and Chloroplast Microsatellites

Abstract

background and Purpose: Natural stands of pedunculate oak in Croatia have been delineated in seed areas, zones and regions. The current bylaw recommends that the transfer of reproductive material remains limited within zones, but that it is permitted within areas. Clonal seed orchards (CSOs) of pedunculate oak were established to increase genetic quality of seed and to acquire a more regular seed yield than in natural stands. In total 150 plus trees were selected within three seed regions. The selection included a number of favourable traits of tree size and stem quality. Three CSOs were planted with grafted plus-trees. We aimed to establish whether these orchards encompass enough genetic diversity to potentially produce genetically improved and sufficiently diverse reproductive material. We also wanted to assess neutral genetic differentiation between these orchards and compare it with the genetic diversity obtained from chloroplast DNA markers, depicting conserved lineages from recolonization routes. We wanted to investigate spatial genetic structure in the area of our research and provide additional information on the transfer of forest reproductive material. Materials and Methods: Leaves were collected from all clones in the CSOs. Total genomic DNA was extracted and clones were analysed with eight nuclear and ten chloroplast microsatellite markers. Spatial autocorrelation analysis was performed with nuclear microsatellite data and original plus trees' coordinates, for each CSO separately, to determine whether shared favourable traits among the selected plus trees in smaller distances are the results of relatedness, which the sampling strategy tried to avoid. results: We found 28 chloroplast haplotypes belonging to four maternal lineages, and significant differentiation between CSOs, indicating origin from different refuges. Nuclear microsatellites' diversity in the CSOs is quite high and comparable to diversity found within a recent study of Croatian natural populations. Nuclear microsatellites did not show genetic differentiation between CSOs, i.e. between the seed regions and seed zones they represent. No genetic differentiation was found with nuclear microsatellites among haplotypic lineages. We found no genetic structure within the analysed regions. Conclusions: Lack of differentiation between CSOs found with nuclear microsatellites confirms the permission for transfer of reproductive material between zones within the seed area 1-Lowland Forests. If original differentiation between chloroplast haplotypic lineages was present after recolonization, it was erased by subsequent gene flow. Lack of genetic structure, with nuclear microsatellites within regions indicates successful sampling strategy.

Genetic Diversity and Differentiation of Pedunculate Oak (Quercus robur L.) Populations at the Southern Margin of Its Distribution Range—Implications for Conservation

“…Expected heterozygosity (H e ) across the studied pedunculate oak populations was similar to other populations at the south-east margin. For example, marker QrZAG87 had similar value of H e (0.87) to those observed by Katičić-Bogdan et al [57] (0.87), Morić [58] (0.88), and Muir and Schlötterer [59] (0.89). Based on QTL associated studies [60], locus QrZAG87 is considered to be linked to genome regions responsible for bud burst timing.…”

“…The mean A R in our populations (9.63) was lower than A R measured in Belgium (11.5) considering four mutual loci (QpZAG 9, QrZAG15, QrZAG112, MSQ 13) [54]. Moreover, according to Katičić-Bogdan et al [57], the mean A R in Croatian pedunculate oak populations (12.77) was higher than in the Serbian (9.63), considering eight mutual loci (QpZAG9, QrZAG11, QrZAG30, QrZAG87, QrZAG96, QrZAG101, QrZAG112, and MSQ13). Considering our results, lower A R in comparison to those observed by the aforementioned authors could be explained by the founder effect impact [61].…”

“…In contrast, marker QpZAG110 had smaller H e (0.62) in comparison to Greek (0.74) and Bulgarian (0.84) populations [36]. Marker QrZAG112 had equal H e value (0.81) in our and other studies at the southern margin [36,55,57,58].…”

Studying the genetic structure of Quercus robur forest stands on anthropogenically transformed territories using introns of the β-tubulin gene

“…A certain degree of spatial autocorrelation has been observed for Q. petraea in Denmark (Jensen et al, 2003). However, for Q. robur seed plantations the spatial correlation was not observed (Katičić et al, 2018). Thus, on the basis of the assessed spatial genetic structure of the tree stands of the "Holosiivsky" NNP we can conclude that there are both primary elements of the spatial structure characteristic for natural populations and populations under anthropogenic influence, which most likely consist of planting of a specific seed material (Katičić et al, 2018) and possibly selective felling.…”

Genetic Diversity and Genetic Structure of Three Sympatric Oak Species in Serbian Landscape of Outstanding Features "Kosmaj" Assessed by Nuclear Microsatellites

“…Genetic diversity loss became particularly important in the context of climate change, relevant also for the production of well-adapted reproductive material used for reforestation (Ivetić et al 2016, Katičić Bogdan et al 2018, Popović et al 2022. Information on genetic variability, genetic structure, and inbreeding is therefore required for the effective management of forest populations (Craft and Ashley 2007).…”