Floral scents of series of Vulgares and Pinnatifoliae in Syringa and linkages to interspecific sibship

Background/Question/Methods Complete information on floral volatiles at hierarchy of series under genus is sparse although floral scents have been studied for a long time. It is also challenging to explore interspecific relationship through volatile products of secondary metabolisms, besides giving the reason of limited geographical distribution for an endangered species from volatile aspect. For a kind of well-known and world-wide cultivated aromatic woody plants, it is necessary for Syringa to identify the floral volatiles for practical use and also interested to explore interspecies linkage from volatiles especially at hierarchy of series under genus on the basis of systematic collections of Syringa. We expected to (1) explore characteristics of volatile blend of Vulgares and Pinnatifoliae Series of Syringa genus, (2) reveal floral volatile restriction of an narrowly-distributed and endangered species, and (3) determine the interspecies relationship and find the linkage between volatile blends and  morphological traits based on volatile cluster analysis and verify its reliability via comparison with the published result of chloroplast DNA phylogenetic analysis. The floral volatiles of seven species of Series Vulgares and Pinnatifoliae of Syringa were sampled with headspace tube in the morning and immediately determined by gas chromatography-mass spectrometry (GC–MS). Clustering for seven species was conducted in order to reveal the interspecies relationship.

Results/Conclusions  Trans-ocimene, linalool, cis-linalool oxide and trans-linalool oxide were predominant for those species which are characterized by fasciculate or lobed leaf, indigotic coronal with long inflorescence and dense ground branching. S. vulgaris has rich monoterpenes and S. oblata had higher content of trans-ocimene, sesquiterpenoids and benzenoids. S.×persica has closer relationship with S. vulgaris, while S.×laciniata tends to S. protolaciniata from floral scent perspective. Quite different compositions of floral volatiles were presented within Vulgares Series and across series of Vulgares and Pinnatifolia. Endangered S. pinnatifolia was only predominant in lilac alcohol B and lilac aldehyde B and their isomers, probably impairing pollinator attraction and limiting pollen diffusion. Interspecific relationship across series of Vulgares and Pinnatifolia constructed depending on floral scents is verified to be reliable and provide helpful references to identify the   interspecies phylogenetic relationship of Vulgares and Pinnatifolia.