Growth and drought stress tolerance in a provenance trial with red oak and selection of plus trees

Background and Objective

RubraSelect will lay the foundation for the production and delivery of high quality reproductive material of
Quercus rubra L. for Germany in the face of climate change. The project aims at the selection and
propagation of trees with superior phenotypes (plus trees) considering their geographic origin as well as
their genetic diversity and adaptive potential. The selection of plus trees will be conducted in planted stands
and in provenance trials based on quality, growth, vitality and genetic marker (Single Nucleotide
Polymorphism, SNP) information. Additionally, plus trees will be characterized at selected biomarkers to
assess their adaptive potential. Progeny trials will be established to test for differences in drought tolerance
among plus tree progenies.
Finally, the genetic basis of growth characteristics and drought stress tolerance will be analysed in a
seedling trial under controlled conditions. Specifically, metabolome and transcriptome and genome
analyses will be used for the development of new drought stress markers responsible for the adaptation to
drought stress conditions. Genome-wide association analyses of genetic variation with trait variation
(drought related traits, metabolites) will be conducted to identify and validate gene markers for growth and
drought stress adaptation.

Approach

The work-packeges of the sub-project of the Thünen Institute of Forest Genetics are
(1) the recording of the phenotypic variation depending on different site conditions (WP7),
(2) the analysis of the reaction of the increase in diameter during and after years of drought (WP9) and
(3) the selection of plus trees and their vegetative propagation as the basis for the establishment of a seed
orchard (WP10) and
(4) reports and presentations of the results in journals and at conferences (WP11)

Results

• Provenance differences in growth and climate sensitivity along the environmental gradient of the three sites enabled the identification of provenances suitable for the identification of high-quality forest reproductive material for forestry practice.
• Significant provenance-environment interactions allowed the identification of generalists and specialists, leading to improved provenance recommendations.
• Tree ring analysis identified summer drought as a growth-limiting factor and a dependence of growth on spring temperatures.
• The response in wood anatomical characteristics showed a high plasticity depending on site conditions and thus the broad site amplitude of this tree species. No signals of local adaptation were observed.
• German provenances were characterized by a high growth performance and a high tolerance to late frost. Drought tolerance was slightly lower compared to slow-growing provenances. Due to their superior characteristics at all three sites they were classified as suitable generalists for implementation in provenance recommendations.
• Provenances from Canada proved to be specialists on the continental site with a high tolerance to drought. This observation is promising for refreshing the genetic diversity in the face of the predicted rising temperatures.
• Provenances from the southern part of the natural distribution are not suitable for cultivation in Germany due to the overall poor performance in adaptive traits.
• Differences in the timing of bud break indicated that selection processes already occurred in German provenances, increasing adaptation to late frosts.
• Harvesting and repeated vegetative propagation of 50 plus trees did not produce the desired growth success, so that the number of grafts is insufficient to establish a seed orchard.