Abstract/Summary

Among the Fragaria species, the cultivated strawberry Fragaria × ananassa (2n=8x=56) is the most economically valuable crops. After harvest, they are extremely perishable, have a short shelf life, and are susceptible to mechanical injuries and physiological decay due to loss of tissue integrity, sensitivity to fungal diseases, and have a large surface area, which lacks an outer protective rind. Therefore, maintaining high nutritional values in the berry fruit whilst maintaining high fruit quality requires an understanding of the genetic and environmental effects on each trait, and how different traits are associated with each other. Mapping traits on the linkage map using a Quantitative Trait Loci (QTL) approach is the first step to identify the underlying gene(s) and to explore their effects and interactions. It will improve our understanding of the genetic control of measured traits and facilitates molecular marker development. Therefore, it can be used to improve plant-breeding efficiency at the molecular level, which significantly reduces the breeding time and cost of phenotyping. The overall aim of this study was to characterise the variation in quality traits among the F1 mapping progeny derived from a cross of Redgauntlet x Hapil (RGxH) strawberry cultivars. These traits include total soluble solids (TSS), titratable acidity (TA), fresh weight, surface colour, firmness, and phenolic content. This thesis presents two areas of work. First, using a novel high-density single nucleotide polymorphism (SNP) linkage map, phenotyping plant characteristics of RG x H progeny enabled the detection of QTL linked to traits associated with shelf life (at 4 °C). Subsequent QTL analysis highlighted 47 QTL linked to quality traits associated with three post-harvest days in two sequential seasons (2013 and 2014). Among them, three major QTL for fruit lightness (L*value) and TSS/TA ratios were detected in 2013, whereas 17 major QTL were detected in 2014, of which three accounted for >30 % of phenotypic variance. Study results provided additional data on the genetic architecture of fruit quality traits across shelf life at points relevant for strawberry breeding. However, it is still necessary to confirm the stability of the identified QTL resulting from the study findings. Second, the study evaluated the flavour profiles of seven genotypes of the RGxH F1 strawberry population and their parental lines in order to assess correlations between sensory and instrumental data. Ten trained sensory panellists rated strawberry puree samples on day 1 and day 5 of storage. Thirty attributes were evaluated, including odour, taste, flavour, mouth sensation and aftertaste. Gas chromatography systems were coupled with the solid-phase micro extraction (SPME) method to determine volatility of organic compounds. The results showed a clear separation between desirable attributes, which correlated with most day 1 samples, and undesirable attributes, which correlated with most day 5 samples. Furthermore, the results confirmed the role that volatile compounds (mainly esters, terpenes and aldehydes) and some physical traits (mainly TSS, TA and their ratios) play in sensory perception.