Phenotypic diversity of Spanish apple (Malus x domestica Borkh) accessions grown at the vulnerable climatic conditions of the Ebro Valley, Spain

• There is a wide variability in the apple Germplasm Bank.
• The study provides information for agronomic, morphological and fruit quality traits.
• This data could be used by breeders to select the most interesting genotypes.
• Several accessions with the same allelic profile exhibit phenotypic differences.
• Relevant accessions could be selected under the Spanish vulnerable climatic conditions.

Agronomic, morphological and fruit quality traits were studied for 80 accessions from an apple Germplasm Bank established at the Experimental Station of Aula Dei, located in the central part of the Ebro Valley (Northeastern Spain, Zaragoza). This area is characterized by low-medium altitude, warm summers with hot day–night temperatures, cold winters and low annual precipitation. Most accessions were surveyed during the last decades from Spanish regions with different climate environments. Agronomic traits included bloom and harvest dates, while morphological traits included different fruit shape and size characteristics. Fruit quality parameters included percentage of over color, chromaticity parameters (L*, a*, b*, C* and h*), flesh firmness, soluble solids content and titratable acidity. Extensive variability was observed for most traits with significant correlations identified between many traits. Principal component analysis (PCA) revealed the main sources of variability in the set of accessions evaluated. Based on these sources, the cluster analysis produced six different groups of accessions according to the Ward's minimum variance criterion. Eight groups of synonymies were found which represented 21% of the total accessions studied. On the contrary, some accessions with the same allelic profile exhibit phenotypic differences, suggesting the existence of clonal mutations not detected with molecular markers. This study provides useful information for agronomic, morphological and fruit quality traits from a wide range of accessions grown under the Ebro Valley vulnerable climatic conditions. In addition, the most interesting materials could be used in breeding programs as parental genotypes to obtain apple cultivars with better adaptation to the limiting Spanish agro-climatic conditions.