Exploration and evaluation of morphological traits and primary metabolites of tetraploid seedlings from Hongkong kumquat (Fortunella hindsii Swingle)

To explore tetraploid seedlings from polyembryonic Hongkong kumquat (Fortunella hindsii Swingle), we screened eight putative tetraploids (doubled diploids) from 1289 seedlings based on root, leaf, and oil gland morphology. Flow cytometry and molecular identification showed that these tetraploids were all autotetraploids, with a screening accuracy of 100% and natural occurrence rate of 0.62%. Compared with diploids, the tetraploids of Hongkong kumquat showed significantly lower plant height, stem diameter, internode number, internode length, and stomatal density, but higher leaf thickness and stomatal size. In addition, leaf primary metabolites between the tetraploids and corresponding diploids were analyzed by gas chromatography-mass spectrometry (GC-MS). Among the 24 detected primary metabolites, the content of quininic acid in the tetraploid leaves was significantly higher than that in the diploid leaves, while the contents of inositol, 4-aminobutyric acid, and 1-monopalmitin were significantly lower.