Figures (5)  Tables (5)

    • Figure 1. 

      Probability density curves for eight apple fruit phenotypic traits across three years (2020–2022). Note: Each subplot shows the fitted normal distribution of the trait for each year (2020: blue, 2021: green, 2022: red). Curves are shaded to visualize the distribution range. Arrow annotations mark the mean value shift among years, indicating trends in trait changes over time.

    • Figure 2. 

      Correlation heatmap of eight apple fruit phenotypic traits.

    • Figure 3. 

      Results of a LDA of the phenotypic traits of apple germplasm resources in three years.

    • Figure 4. 

      LDA coefficients per germplasm type.

    • Figure 5. 

      Circular hierarchical clustering tree based on phenotypic traits. (a) 2020; (b) 2021; (c) 2022.

    • Year Trait Mean Std SE Min Max CV H′ ANOVA p-value
      2020 Fruit weight (g) 82.63 82.05 3.62 0.71 354.00 0.99 1.68 0.001
      2021 100.20 87.88 3.88 0.62 409.60 0.88 1.71
      2022 80.84 82.79 3.50 0.42 392.29 1.02 1.61
      2020 Firmness (kg/cm2) 7.52 2.65 0.12 1.88 15.78 0.35 1.99 0.950
      2021 7.75 2.62 0.12 1.71 17.53 0.34 1.89
      2022 5.79 2.48 0.11 1.06 16.00 0.43 1.77
      2020 Soluble solids (%) 13.90 4.34 0.19 7.71 37.24 0.31 1.51 0.100
      2021 13.75 3.88 0.17 8.44 37.30 0.28 1.40
      2022 14.33 5.37 0.23 7.13 36.53 0.38 1.64
      2020 Titratable acidity (%) 0.89 0.55 0.02 0.08 4.15 0.62 1.54 0.003
      2021 0.81 0.53 0.02 0.11 5.47 0.66 1.19
      2022 0.93 0.66 0.03 0.09 3.88 0.71 1.74
      2020 Vitamin C (mg/100g) 8.21 5.55 0.25 0.20 55.08 0.68 1.28 0.261
      2021 8.73 5.79 0.26 0.75 44.34 0.66 1.49
      2022 8.76 6.95 0.29 1.54 71.47 0.79 0.93
      2020 Soluble sugar (%) 8.44 2.85 0.13 1.04 26.73 0.34 1.49 0.010
      2021 9.63 2.38 0.11 2.23 17.07 0.25 1.84
      2022 4.75 1.93 0.08 0.74 11.50 0.41 1.97
      2020 Sugar-acid ratio 15.08 13.86 0.61 0.83 106.89 0.92 1.27 0.010
      2021 18.51 15.00 0.66 0.84 88.12 0.81 1.65
      2022 8.15 7.67 0.32 0.43 64.72 0.94 1.15
      2020 Solid-acid ratio 23.19 19.52 0.86 3.98 163.11 0.84 1.15 0.074
      2021 25.03 18.78 0.83 3.42 122.22 0.75 1.54
      2022 22.57 16.44 0.70 4.05 139.68 0.73 1.27
      Std: Standard deviation; SE: Standard error; Min: Minimum; Max: Maximum; CV: Coefficient of variation; H′: Shannon-Wiener diversity index.

      Table 1. 

      Variations in fruit traits among germplasm resources in 2020, 2021, and 2022.

    • Trait Eigenvector of the principal component
      PC1 PC2 PC3 PC4 PC5 PC6 PC7 PC8
      Fruit weight (g) 0.394 −0.208 −0.046 −0.070 0.714 −0.534 0.003 0.002
      Firmness (kg/cm2) −0.079 0.498 −0.583 0.291 −0.212 −0.524 0.039 0.005
      Soluble solids (%) −0.201 0.476 0.498 −0.419 −0.006 −0.332 −0.403 −0.191
      Titratable acidity (%) −0.488 0.138 0.219 −0.075 0.228 −0.114 0.776 0.147
      Vitamin C (mg/100g) −0.252 0.008 0.368 0.826 0.233 −0.019 −0.252 −0.014
      Soluble sugar (%) 0.158 0.613 −0.154 −0.030 0.468 0.520 −0.083 0.280
      Sugar-acid ratio 0.491 0.270 0.215 0.183 −0.084 0.102 0.383 −0.665
      Solid-acid ratio 0.480 0.119 0.396 0.110 −0.337 −0.188 0.128 0.649
      Eigenvalue 3.059 1.693 0.965 0.917 0.614 0.465 0.249 0.042
      Contributive percentage (%) 38.216 21.143 12.053 11.459 7.673 5.814 3.114 0.527
      Total cumulative (%) 38.216 59.359 71.412 82.871 90.544 96.358 99.473 100.000

      Table 2. 

      Principal component analysis of eight apple fruit phenotypic traits.

    • Germplasm type Year Fruit weight
      		 Firmness
      		Soluble solids Titratable acidity Vitamin C
      		 Soluble sugars Sugar-acid
      ratio      		 Solid-acid
      ratio      		 Mean
      Wild germplasms 2020 97.67 37.12 40.88 50.46 68.81 44.86 90.45 78.99 63.66
      2021 114.03 38.38 39.58 47.33 62.01 32.74 88.77 76.00 62.36
      2022 131.92 42.22 47.22 55.00 88.17 39.28 109.53 79.55 74.11
      Landraces 2020 91.80 35.76 25.78 44.75 61.19 30.46 77.49 70.51 54.72
      2021 98.65 29.31 22.07 71.22 58.15 20.76 65.63 63.67 53.68
      2022 87.31 41.53 26.52 50.60 55.86 36.19 73.96 57.96 53.74
      Cultivars 2020 40.36 28.86 14.64 55.60 56.38 20.89 72.15 73.29 45.27
      2021 38.69 28.62 12.18 51.39 44.08 14.78 63.36 62.62 39.46
      2022 37.55 28.14 12.35 55.44 47.07 40.61 81.63 58.52 45.16

      Table 3. 

      Coefficient of variation (%) of eight fruit traits of three apple germplasm types.

    • Germplasm typeYearFruit weight
      (g)      		Firmness
      (kg/cm2)      		Soluble solids
      (%)      		Titratable acidity
      (%)      		Vitamin C
      (mg/100g)      		Soluble sugars
      (%)      		Sugar-acid
      ratio      		Solid-acid
      ratio
      Wild germplasms202029.87± 29.177.46 ± 2.7713.96 ± 5.711.21 ± 0.619.94 ± 6.847.57 ± 3.48.58 ± 7.7614.84 ± 11.72
      202135.64 ± 40.647.60 ± 2.9213.79 ± 5.461.15 ± 0.5412.0 ± 7.448.42 ± 2.769.79 ± 8.6915.12 ± 11.49
      202227.13 ± 35.795.79 ± 2.4516.05 ± 7.581.39 ± 0.7711.38 ± 10.044.76 ± 1.875.19 ± 5.6914.89 ± 11.84
      Landraces202035.96 ± 33.018.47 ± 3.0315.38 ± 3.970.85 ± 0.387.38 ± 4.528.75 ± 2.6713.59 ± 10.5322.90 ± 16.14
      202134.71 ± 34.249.27 ± 2.7215.86 ± 3.50.86 ± 0.617.75 ± 4.5111.10 ± 2.3017.29 ± 11.3524.23 ± 15.43
      202231.81 ± 27.777.12 ± 2.9615.30 ± 4.060.93 ± 0.478.12 ± 4.535.57 ± 2.027.59 ± 5.6219.80 ± 11.47
      Cultivars2020169.91 ± 68.576.98 ± 2.0112.87 ± 1.880.56 ± 0.316.85 ± 3.869.18 ± 1.9223.09 ± 16.6632.42 ± 23.77
      2021174.24 ± 67.427.31 ± 2.0912.94 ± 1.580.53 ± 0.276.56 ± 2.8910.04 ± 1.4825.72 ± 16.2933.01 ± 20.67
      2022171.53 ± 64.414.72 ± 1.3311.89 ± 1.470.49 ± 0.276.78 ± 3.194.08 ± 1.6611.42 ± 9.3332.14 ± 18.81

      Table 4. 

      Multiple comparison results for eight apple fruit traits in different years.

    • Trait Index sum_sq df F PR (> F)
      Fruit weight Year 5,259.154 2 1.089 0.337
      Population 76,809,08.927 2 1,591.183 0.000
      Year × population 2,054.331 4 0.213 0.931
      Firmness Year 1,439.233 2 117.838 0.000
      Population 886.503 2 72.583 0.000
      Year × population 56.664 4 2.320 0.055
      Soluble solids Year 37.591 2 0.710 0.492
      Population 3,538.400 2 66.813 0.000
      Year × population 266.875 4 2.520 0.040
      Titratable acidity Year 1.274 2 2.127 0.120
      Population 201.086 2 335.626 0.000
      Year × population 1.944 4 1.622 0.166
      Vitamin C Year 275.571 2 3.892 0.021
      Population 5,781.692 2 81.648 0.000
      Year × population 397.030 4 2.803 0.025
      Soluble sugar Year 7,394.789 2 700.748 0.000
      Population 524.423 2 49.696 0.000
      Year × population 428.014 4 20.280 0.000
      Sugar acid ratio Year 25,811.178 2 106.270 0.000
      Population 50,140.245 2 206.437 0.000
      Year × population 6,321.958 4 13.014 0.000
      Solid acid ratio Year 454.807 2 0.844 0.430
      Population 99,950.577 2 185.583 0.000
      Year × population 924.909 4 0.859 0.488
      Index: Source of variation year, population, and their interaction (year × population); sum_sq: Sum of squares, indicating the contribution of each factor to total variation; df: Degrees of freedom; F: F-statistic used for significance testing; PR (> F): p-value, with values less than 0.05 considered statistically significant.

      Table 5. 

      Two-way ANOVA results for eight fruit traits across different germplasm types and three years.