Phenotypic analysis of fruit quality traits and effect of climate in an apple (Malus × domestica Borkh) germplasm bank of Aragón, Spain

Apples are among the most widely consumed fresh fruits in the world. They are highly appreciated in terms of flavor, nutritional and health-promoting compounds. Bioactive molecules are associated with a reduced risk to develop diseases. In this study, a total of 155 accessions of Malus × domestica Borkh from an apple Germplasm Bank established at the Experimental Station of Aula Dei, located in the Ebro Valley (Northeastern Spain, Zaragoza) were studied. Basic fruit quality traits as soluble solids content (SSC), titratable acidity (TA) and the ratio SSC/TA (ripening index – RI), were analyzed. Biochemical traits as total phenolics content (TPC), flavonoids, vitamin C and relative antioxidant capacity (RAC) were also determined for five consecutive years. Using R software, an ANOVA analysis, Pearson’s correlations and a principal components analysis (PCA) were constructed. In addition, a mixed-effects model was constructed. Trait values differed significantly among accessions and years. Each different trait was used as dependent variable in the model (only TPC is discussed), the climate features as independent variables or fixed effects, and the variety as random effect. Using the Akaike Information Criterion (AIC) statistic, the best significant model was selected. It included precipitation (although non-significant), minimum daily temperature and solar radiation. The R² of the model was 0.85, and the mean absolute error (MAE) was 5.75. A cluster analysis was performed on the model coefficients space to classify the 155 accessions, using the Ward’s D method based on the Euclidean distance. A solution with 5 groups was selected as optimum. The foreign accessions were concentrated in two groups. In general, the bioactive compounds values tended to decrease with highest temperatures meanwhile to increase with higher solar radiation. Statistical analyses highlighted accessions and climate as main factors affecting metabolite profile and fruit characteristics.