Phenotypic variations in fruit traits among different Malus germplasm types

Apple germplasm resources exhibit substantial genetic and phenotypic diversity, offering great potential for fruit quality improvement. In this study, 1,217 apple accessions representing wild germplasms, landraces, and cultivars were systematically evaluated over three consecutive years (2020–2022) for eight key fruit traits, including fruit weight, firmness, soluble solids, titratable acidity, vitamin C, soluble sugar, sugar-acid ratio, and solid-acid ratio. High coefficients of variation and Shannon-Wiener indices were observed for several traits, particularly fruit weight, soluble sugar, and titratable acidity, reflecting rich genetic variation. Correlation analysis revealed strong interdependence among flavor-related traits, while vitamin C appeared genetically independent. PCA and LDA effectively differentiated germplasm types and highlighted key trait contributions. Wild germplasms showed the highest diversity, while cultivars exhibited more uniform traits due to intensive breeding. ANOVA confirmed significant genetic effects on key traits, with certain traits (e.g., titratable acidity, fruit weight) showing high interannual stability, while others (e.g., soluble sugar, firmness) were environmentally influenced. Hierarchical clustering revealed genotype-environment interactions and geographic differentiation, such as distinct trait patterns among Malus germplasms from different regions. This comprehensive phenotypic assessment provides valuable insights for apple breeding, germplasm selection, and genetic resource conservation, emphasizing the importance of wild germplasms and landraces in expanding the genetic base of cultivars.