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Breeding in red raspberries is hampered by genetic incompatibility between varieties and a long juvenility period. Molecular breeding efforts in red raspberry have provided viable applications to incorporate disease resistance in new varieties. This approach could also be applied in developing non-GM strategies to improve flavour quality of red raspberries, successful in other related fruit crops (e.g. peach, apple), with 'good' flavour quality determined by sensory panellists. In this study, sensory data was correlated to data on flavour metabolites (e.g. sugars, organic acids and volatiles) through statistical modelling, which yielded possible causal relationships. These flavour traits data were then mapped to genetic loci and / or candidate genes on an already existing raspberry genetic linkage map and generated genomic regions most likely responsible for trait variation, potentially genetic markers for flavour quality. These markers could be used to select seedlings w ith propensity to develop premium flavour quality prior to planting, thus reducing time required to produce new varieties. This study aimed to investigate flavour development in red raspberry cross population (Glen Moy x Latham) impacted by environmental (different year and cultivation methods) and genetic (different genotypes in a cross mapping population) factors. Flavour metabolites; sugars and acids contents, were quantified via chromatographic methods (HPLC-UV/Vis, HPLC-MS) and other flavour-related datasets (oBrix, 10-berry weight, volatiles and pigment-related contents) were obtained from parallel researches. These datasets were correlated to sensory scorings (sweetness, sourness and flavour intensity) of progenies in the mapping populations, via statistical regression analyses (PLS-1), in order to identify factors most responsible for variances in flavour traits. Genetic explanations of flavour quality were obtained through mapping sweetness, sourness and flavour i ntensity and flavour-related datasets to the red raspberry genetic linkage map (Graham et al., 2009) which yielded flavour-related quantitative trait loci (QTLs). Overall, polytunnel cultivation was most effective in producing fruits with high flavour scores and metabolites contents. Sweetness and flavour intensity, both closely linked, were significantly correlated to sugars content, with notable contributions by volatiles content, especially hexenol. Raspberry ketone (RK) had compounded effects with other metabolites in impacting sweetness and flavour intensity but not sourness. Sourness was a complex trait poorly explained by metabolites content or any other flavour-associated variable. Linkage group (LG) 3 had most number of QTLs that co-localised to markers associated to processes affecting overall plant growth and to biosynthetic pathways of other flavour compounds (e.g. phenypropanoid pathways for volatiles). These results indicate flavour quality development as a complex trait and many factors affect it. Although genetic selection for improved flavour quality is possible, effects from genetic x environmental interactions most impact on flavour quality, with clear advantage of developing good flavour berries with increased metabolites under polytunnel cultivation. Results from this study add to knowledge on factors affecting red raspberry flavour, which could assist breeders in developing control strategies and help focus future breeding efforts on factors that most impact on flavour quality. Furthermore, results from this study can be transferred to other Rosaceae species and add to existing efforts to develop modern flavour quality management strategies. |
