Evaluation of fruit phenotypic diversity in 210 Malus sieversii germplasm resources

This study utilized 210 Malus sieversii germplasm fruit samples collected from seven natural populations, which exhibit rich genetic diversity in their hereditary traits. The research findings systematically evaluated and identified the genetic diversity of 31 fruit phenotypic traits using five statistical analysis methods: frequency analysis, quantitative trait statistical analysis, correlation analysis, principal component analysis (PCA), and cluster analysis, thereby enabling the screening of distinctive germplasm resources. Frequency distribution analysis revealed that a high proportion of the samples had fruit weight ranging from 10-20 g, fruit longitudinal diameters from 25-31 mm, fruit transverse diameters from 30-39 mm, pedicel length from 10-20 mm, and soluble solids content (SSC) from 11.4%-13.75%. The fruit shape of M. sieversii is predominantly "oblate" or "oblique", with the ground color mostly "green-yellow", flesh color mostly "green-white", and flavor predominantly "sour". Statistical analysis of quantitative traits revealed that the coefficient of variation for eight quantitative traits ranged from 7.02%-38.24%. Among these, fruit weight and pedicel length exhibited relatively high coefficients of variation, indicating rich genetic diversity. Correlation analysis showed that fruit weight was significantly positively correlated with fruit longitudinal diameters, fruit transverse diameters and pedicel diameter, while pedicel length was significantly negatively correlated with pedicel diameter. Fruit ground color showed significant negative correlations with flesh color and juiciness. PCA extracted 12 principal components with a cumulative contribution rate of 68.43%. Among these, the first four principal components - fruit size, flavor quality, basin morphology, and pedicel characteristics - were identified as the main dimensions constituting the phenotypic diversity of M. sieversii fruits. The 210 germplasm resources were classified into four clusters: Cluster I comprised small-fruit, high-acidity resources; Cluster II, resources with long pedicel traits; Cluster III, oblate-shaped, short-pedicel resources; and Cluster IV, specific resources characterized by large fruit size and favorable flavor quality. The results provide a theoretical basis for the effective utilization of M. sieversii germplasm resources and offer references for the selection and breeding of specific resources.