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.