From valley to mountain: Organoleptic and nutritional properties of apple accessions from Northeast Spain

• Local cultivars showed high biodiversity in organoleptic and nutritional qualities. • Altitude impacts apple fruit quality by modifying firmness, sugars, and phenolics. • Autochthonous accessions are key for adapting fruit traits to environmental conditions. • Fructose concentration increases with altitude in most apple accessions studied. • Ploidy, origin, and growing altitude are key factors shaping apple traits. Local apple accessions are vital for their adaptability to specific climates and unique organoleptic characteristics, playing a key role in biodiversity conservation and agricultural resilience. This study examined 36 apple genotypes from the CITA collection, including 25 diploid and 11 triploid varieties distributed across five altitudes in northeastern (NE) Spain. The collection encompassed both autochthonous landraces and non-Spanish commercial cultivars. The analysis focused on physicochemical attributes such as fruit firmness, total phenolic content (TPC), and individual sugars. Among these six genotypes (five autochthonous landraces and one commercial cultivar used as reference ‘Gala’), were present at two different altitudes within the CITA collection and were further evaluated to assess the influence of altitude elevation on these traits. Significant variability in fruit quality was observed, with notable correlations between physicochemical traits. Principal component analysis (PCA) explained 50.2% of the total variance, highlighting genetic variability among the accessions and its impact on fruit traits. The results showed that ploidy (diploid/triploid) and origin (autochthonous/commercial - non-Spanish) are key factors shaping apple characteristics. Higher altitudes were associated with increased TPC in specific accessions, likely due to cooler temperatures and greater UV and sun exposure enhancing phenolic biosynthesis. Fructose content also increased with altitude, reflecting slower fruit development and ripening, while variations in glucose and sucrose indicated the complexity of metabolic responses to both altitude and genetic factors. These findings demonstrate the high biodiversity of apples from NE Spain, particularly in terms of their organoleptic and nutritional qualities. Preserving autochthonous apple resources is essential, and breeding programs could benefit from selecting accessions with desirable biochemical traits for local climatic conditions. Additional research is needed to explore how environmental factors influence the health benefits of apples, especially their bioactive compounds, as well as their agronomic performance.