GENOMIC APPROACHES AND PHENOTYPIC ANALYSES FOR IMPROVING THE SELECTION OF FRUIT QUALITY TRAITS IN PEACH [PRUNUS PERSICA L. (BATSCH.)] AND APRICOT (PRUNUS ARMENIACA L.)

Peach [Prunus persica L. (Batsch.)] and apricot (Prunus armeniaca L.) are two Prunus species developing delicious fruits and they are mostly grown in temperate areas of the world. Both species have been cultivated since ancient times, being greatly appreciated for their unique taste and benefits to human health. Peaches and apricots can be consumed either fresh or processed through canning or drying, depending on the preference of a specific region and the use-purpose. So far, many efforts have been done in enhancing disease and pest resistance, in increasing the environmental adaptability to sub-tropical areas, in extending the harvest season or in improving fruits appearance. However, consumers frequently complain about the lack of taste in peach and apricot fruits sold on markets, encouraging the ongoing breeding projects to include organoleptic properties among their objectives. Among all the fruit quality-related traits, acidity plays a pivotal role affecting both consumers’ and market acceptance. To match with market trends, an extensive characterization of peach and apricot fruits attributes under the highlighted necessity of renewing the varieties cultivated worldwide is required. In this thesis, a peach and apricot collection of 201 and 164 accessions, respectively, was screened for many important fruit organoleptic attributes, with a specific focus on acidity and organic acids content. Fruits acidity was titrated and ten organic acids (cis-aconitate, citrate, fumarate, galacturonate, malate, oxalate, quinate, shikimate, succinate and tartrate) separation was accomplished by HPLC technique coupled to UHPLC-HRMS validation. Analyses were performed on peach pulp and on apricot pulp and peel. The final aim was in-depth dissecting the peach and apricot panel for these organoleptic parameters to exploit the existing variability within their germplasm. Malate and citrate were the most abundant organic acids in both species, with pattern more genotype than year dependent. Results suggested that seasonality effects on fruits acidity and almost all the considered-organic acids were very low. Among the other organic acids, quinate and succinate reached large concentrations in peach and apricot, respectively, while tartrate was interestingly present more in apricot peel than pulp. The availability of a reference genome in peach has allowed to further characterize peach fruit quality traits. Over the past, peach fruits acidity has been partially elucidated at genetics level, identifying one major locus and making it a breeding target. Although the great advances, the selection accuracy and the long-time required for releasing new varieties on markets still hamper peach breeding progress. To in-depth unravel acidity trait and to speed up the selection of newly developed individuals in peach, a total of 1,190 accessions were genotyped for performing genomics analyses. Two different studies were carried out in this thesis: genomic selection (GS) and genome wide association studies (GWAS). Results confirmed that GS seems feasible in peach not only for acidity but also for organic acids content, in particular for patterns of malate and citrate. GWAS confirmed the presence of one major locus acting as dominant in peach fruits but revealed other significant associations on chromosomes 1, 7 and 8. In summary, this thesis includes the first efforts in an in-depth and at multilevel dissection of acidity in peach and apricot, applying different approaches on a large panel of individuals. This thesis attempts to provide a complete overview with results that may be useful for future researches, studies and successful breeding programmes.