Exploring horticulturally important traits in apple using genetic mapping in populations of differing size and composition.
Apple (Malus x domestica Borkh.) is a long-lived woody perennial important to international markets. Development of new apple cultivars historically has been protracted and expensive, largely due to its biology. We believe that locating markers linked to traits of interest and marker-assisted selection (MAS) at the seedling stage could accelerate this process. Quantitative trait locus (QTL) mapping and genome-wide association studies (GWAS) for traits important to the sustainability and longevity of the Canadian apple industry, such as storage disorders, disease resistance, and fruit quality were conducted in three populations. Two QTL associated with the storage disorder soft scald were detected in the parental background of one F1 cross, but were not replicated across years, or when GWAS were conducted in a different population. Apple scab (Venturia ineaqualis [Cke.] Wint.) is a fungal pathogen that plagues growers in wet, humid climates, such as Nova Scotia. Significant genotype-phenotype GWAS associations were detected across seven different chromosomes for apple scab resistance in a germplasm collection of commercial cultivars. In the same population, GWAS also revealed SNPs associated with fruit quality traits, such as apple fruit skin colour and change in firmness during storage. Finally, a large, diverse germplasm collection and GWAS were used to explore flowering time and fruit quality. Significant marker-trait associations were found for flowering time in two years, but no clear candidate genes were identified. Fruit quality studies revealed several significant genotype-phenotype associations, including harvest date, fruit firmness, and acidity. This research will form the foundation of future studies for the development of markers that will assist with the development of new apple cultivars well-suited for Canadian and international markets.