Identification of molecular markers associated with winter survival in the cultivated strawberry

A crucial consideration for strawberry producers in Norway and other northern countries is the winter freezing damage. A long-term goal of the Norwegian strawberry breeding is to increase winter hardiness and improving fruit quality. Due to the complexity involved in the regulation and enhancing freezing tolerance, the progress in the improvement of cultivars using traditional screening methods have had limited success. Thus, the development of molecular markers for freezing hardiness would facilitate the selection work for this trait. For the last three years, Graminor Breeding Ltd. and collaborators have developed and adopted state-of-art molecular tools to investigate cold response in strawberry plants during the acclimation phase resulting in the identification of a large number of genes, proteins, and distinct metabolites that correspond to cold/freezing tolerance in strawberry. In this effort, we have examined alterations in protein levels in four octoploid (cultivated) strawberry cultivars that differ significantly in cold tolerance. Proteomic analysis from two cultivars suggested 50 potential biomarkers (out of 1000 proteins) that showed significant changes in the cultivated strawberry in response to cold. In addition, GC-MS-based metabolite profiling of the model F. x vesca (wild strawberry) revealed the up-regulation of carbohydrates and polyols, amino acids, TCA intermediates but also distinct secondary metabolites in leaves and roots after cold treatment. Moreover, our newer studies in octoploid strawberry (F. x ananassa) have shown similar patterns of metabolic changes in crown tissue upon cold treatment. Transcriptional analysis on known cold regulated genes was done where varietal differences were found. In addition, several F2-populations from parents diverging in cold tolerance have been developed in order to facilitate mapping of QTLs. The parents have been screened for 144 microsatellites spread across the seven linkage groups. Sixty-nine of these showed polymorphy and they will be used in the development of a framework map in one of the F2-populations. Together with phenotype data, this will give indications on where important genes are located in the genome. The knowledge attained from these endeavors is expected to expedite breeding of strawberries to achieve freezing tolerant lines and provide an integrative understanding of the genetics and the metabolic pathways that underlie this characteristic.