3.1.2. PC analysis and evaluation of phenotypic traits
PC analysis was carried out with 26 phenotypic indices, and eigenvalues greater than 1 were selected to obtain a total of seven PCs (Table 4). The contribution rates of these seven comprehensive indicators were 28.13%, 11.44%, 7.932%, 6.85%, 5.91%, 4.79%, and 4.34%, respectively, with a cumulative contribution rate of 69.39%. The results showed that these traits contained the most genetic information among all phenotypic traits, and they could be used for the comprehensive evaluation of genetic resources. The feature vectors of the first PC1 were mainly stem wing (0.124), leaf length (0.118), tuber shape (0.114), tuber endodermis color (0.105), bulbil or not (0.103), and flowering (0.100). PC2 was a comprehensive response of stem, including stem thorn (−0.290) and stem rotation (−0.290). PC3 was correlated with leaf margin color, leaf apex shape, and leaf color, with eigenvector values of 0.284, 0.218, and −0.220, respectively. The feature vectors of PC4 was connected to leaf vein (0.318), petiole color (0.293), leaf width (0.216), and length-to-width ratio (−0.260). These two PCs were comprehensive responses of leaf. The tuber flesh weight (0.369), tuber diameter (0.253), and leaf vein color (0.265) of PC5 had large eigenvector values. PC6 was associated with leaf vein color (0.457), leaf vein (0.300), and root hair distribution (0.383). PC7 was correlated with root hair density (0.556) and root hair distribution (0.386). In accordance with the contribution rate and eigenvalues of the PCs, leaf color, leaf vein, leaf margin color, leaf vein color, leaf apex shape, petiole color, stem wing, and stem thorn were the main factors that caused the phenotype difference in yam germplasm resources. The 20 traits could be regarded as the main phenotypic indicators for the evaluation of yam germplasm resources in the future. Therefore, these traits could also be regarded as the main phenotypic traits in the evaluation of Chinese yam germplasm resources in the future.