Genetic origin and climate determine fruit quality and antioxidant traits on apple (Malus x domestica Borkh)

Apples are highly appreciated in terms of flavor, nutritional and health-promoting compounds and are associated with a reduced risk to develop age-related and chronic diseases. In this study, 155 accessions of Malus x domestica Borkh from the apple germplasm collection, located at the Experimental Station of Aula Dei in NE Spain, were analyzed during five consecutive years (2014-2018). Basic fruit quality traits including soluble solids content (SSC), titratable acidity (TA) and the ratio SSC/TA (ripening index - RI) were obtained. In addition, biochemical compounds such as total phenolics content (TPC), flavonoids (TFC), vitamin C (Ascorbic acid - AsA) and relative antioxidant capacity (RAC) were determined. Statistical analysis was used to determine differences in trait values among accessions and years. The well adapted local accessions showed, in general, higher average content of antioxidants and RAC compared with the foreign and commercial ones. A multivariate model was fitted with the accessions and climate features of each year as independent variables. A cluster analysis was then performed on the model coefficients space to classify the 155 accessions within five groups. The cluster analysis showed that foreign cultivars (those not originating from Spain) were concentrated in two groups while local accessions could not be segregated and had very different profiles. Furthermore, they increased the concentration of bioactive compounds tended to decrease with higher temperatures, while increased with higher solar radiation. Statistical analyses emphasized differences between groups and highlighted accessions and climate as main factors affecting metabolite profiles and fruit characteristics.