Free Volatile Compounds as Chemophenetic Markers—Comparison with ITS2 and ITS1-5.8S-ITS2 Sequence Data for 18 Species of the Genus Veronica

Abstract

(1) Background: The purpose of this study was to compare the free volatile compounds of 18 Veronica species (Plantaginaceae), as previously analyzed by gas chromatography coupled with mass spectrometry, with their DNA sequences for internal transcribed spacers ITS2 and ITS1-5.8S-ITS2 of the nuclear ribosomal DNA. (2) Methods: Two sets of DNA sequence data were generated and used for phylogenetic analysis: ITS2 sequences (~360 bp) obtained by next-generation sequencing and ITS1-5.8S-ITS2 sequences (~580 bp) sequenced by the Sanger sequencing method. Clustering from previously analyzed free volatile compounds was performed by Ward’s method. (3) Results: Both sets of DNA sequence data showed that the 18 analyzed Veronica species were grouped into eight main groups corresponding to the following subgenera: Pentasepalae, Pocilla, Chamaedrys, Veronica, Beccabunga, Cochlidiosperma, Stenocarpon and Pseudolysimachium. Results of the clustering analysis of free volatile compounds showed better clustering when using microwave-extracted volatiles. Three clusters were detected with the following main compounds: hexahydrofarnesyl acetone, hexadecanoic acid, phytol, caryophyllene oxide and (E)-caryophyllene. (4) Conclusion: The phylogenetic analysis of ITS2 data obtained by NGS technology and ITS1-5.8S-ITS2 data obtained by Sanger sequencing resulted in the grouping of 18 Veronica species into eight subgenera, which is in accordance with the existing classification. Statistical testing showed that there was no correlation between such clustering of Veronica species and clustering that was based on free volatile compounds. The achieved results can be viewed in the light of parallel evolution among some of the species of the Veronica genus as well as the fact that volatile compound composition can be influenced by environmental factors or epigenetic modifications.