Abstract/Summary

The cultivated strawberry (Fragaria × ananassa Duch.) is the third most economically important fruit crop. In recent years the withdrawal of many fungicides and soil fumigants have made the sustainability and profitability of this crop more challenging. To overcome these challenges, plant breeders aim to improve upon existing cultivars and to release new ones with higher yield, better fruit quality and more disease resistance. Through Quantitative Trait Mapping, markers linked to genetic variants associated with traits of economic and agronomic importance can be identified through and molecular markers such as simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs), can be used to improve plant breeding efficiency at the molecular level, which significantly reduces the breeding time and cost of phenotyping. In this thesis the following work is described: a correlation analysis of plant characteristics and fruit quality traits; the saturation of an existing SSR-based linkage map; the development of a high density consensus SNP-based octoploid strawberry linkage map, and the identification of quantitative trait loci (QTL) linked to two key plant attributes, fruit quality and powdery mildew resistance. In addition, the most closely linked SSR markers were identified and validated in a wider strawberry germplasm using firmness as an example study. Moreover, the physical locations of expansin genes and SNP markers associated with firmness QTLs were investigated. The purpose of this analysis was to find out if QTLs associated with fruit firmness overlapped the positions of expansins, genes known to be important in controlling fruit firmness.