Genome-wide association mapping for disease resistance and fruit quality traits in Nordic association mapping panel of garden strawberry

Strawberry breeding in Finland began 60 years ago and has largely relied on traditional breeding methods. The geography of Finland, as well as local consumer preferences for darker-coloured strawberries, have been the main focus of selection in all implemented Finnish breeding programs. With several successful and popular cultivars have been released, the current focus is on increasing yield and disease resistance while maintaining the excellent fruit quality of breeders' selections. A panel of 175 garden strawberry accessions was created and trialled at the Natural Resources Institute Finland (Luke) as part of a Nordic-Baltic pre-breeding collaboration between the institute and the Norwegian breeding company Graminor AS. A medium-density, genome-wide scan for 50K SNPs has been performed on each individual of the panel. This panel represents the genetic diversity present and typical for cultivated strawberry in the Nordic-Baltic region, and it is expected to provide Nordic breeders with markers tailored to their plant material diversity, supporting their future selection decisions and accelerating their breeding cycles. In this study, symptom severities of two strawberry leaf diseases (leaf spot caused by Mycosphaerella fragariae and leaf scorch caused by Diplocarpon earlianum) and seven fruit quality traits (berry weight, skin colour, flesh colour, evenness of flesh colour, basket appearance, predominant berry shape and tip type) were scored in the panel. GAPIT and statgenGWAS statistical packages in R were used to run five different GWAS models: Significant SNP-trait associations were found using single-locus (GLM and MLM) and multi-locus (FarmCPU and BLINK) association mapping analyses. The study had shed a light on the importance of considering several statistical models and parameters for a maximum benefit of association mapping studies. Among significant SNP-trait associations for fruit weight, fruit skin colour and fruit flesh colour, four were partially characterized by inspecting their allelic effects. On chromosome Fvb6-1, appearance of consensus, significant signals from the flesh colour trait of secondary-position berries is discussed. Nine significant SNP-marker associations were detected for berry weight.