Distant heteroploid hybridization improved Hedychium floral scent, floral color and morphologcal traits

Heteroploid hybridization is an important breeding technique for producing heteropolyploids with superior traits. Hedychium is widely used in medicine and as an ornamental plant; however, the fact that no current varieties exhibit both fragrance and colorful flowers causes a bottleneck in the genetic improvement of Hedychium. In the current study, diploid Hedychium coronarium 'ZS' (with strong fragrance and white flowers) and tetraploid Hedychium coccineum 'KMH' (scentless with red flowers) were used for the reciprocal heteroploid hybridization, and the 34 flowering hybrid offspring were analyzed for ploidy and hybrid authenticity, phenotype and floral scent. In 'ZS' ♀ × 'KMH' ♂, eight hybrids were triploids, while there were nine triploids and seventeen tetraploids in 'KMH' ♀ × 'ZS'♂. Furthermore, all hybrids were true hybrids as determined by simple sequence repeat (SSR) markers, and the presence of unreduced pollen in 'ZS' flowers was confirmed. Compared with the parents, 15 morphological traits and four flower color traits of hybrid offspring were widely separated. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) showed that the parents and 34 hybrids could be divided into three groups mainly depending on organ size and color intensity. Headspace solid phase microextraction–gas chromatography–mass spectrometry (HS–SPME–GC–MS) identified 16 volatile organic compounds (VOCs), all of which were widely separated in the hybrid offspring. The HCA and PCA results confirmed that the parents and 34 hybrids could be classified into three groups mainly based on linalool, (E)-β-ocimene, eucalyptol, and methyl benzoate. Partial least squares discriminant analysis (PLS-DA) revealed that morphology, floral color and floral scent differed significantly between triploids and tetraploids, and the variable importance in projection (VIP) of 14 indexes was greater than 1. Finally, this study screened four new allopolyploid germplasms (HB30, HB46, HB54 and HB61) with colorful flowers and rich floral scent. These findings suggest a new strategy for cultivating new varieties with strong fragrance and bright colors.