High throughput pre-breeding evaluation of Greek oregano (Origanum vulgare L. subsp. hirtum) reveals multi-purpose genotypes for different industrial uses

Origanum vulgare L. subsp. hirtum (commonly known as Greek oregano) is a perennial species of the Lamiaceae family that counts numerous applications in the food and pharmaceutical industry. The exploitation of Greek oregano germplasm lies in its unique diversity in secondary metabolites, which are accumulated in the aerial parts of the plant. For the industrial exploitation of this crop the starting germplasm is of high importance in terms of valorizing well characterized chemotypes with desired and stable agronomic and phytochemical traits. For this reason, a pre-breeding evaluation of twenty-one accessions collected and preserved under the same environmental conditions was performed in order to develop a descriptive database containing: a) morphometric traits, b) the genetic structure, c) the extensive metabolic fingerprint in terms of volatile composition, polyphenolic and triterpenoid content, and d) the ‘bio-activity’ on the embryonic development of Ascaridia galli eggs for highly divergent accessions. This study revealed the existence of essential oil rich chemotypes superior in morphometric characteristics, containing high carvacrol content (> 75%) and traces of thymol (< 5%), according to the requested international standards. Apart from genotypes considered as ‘high yield essential oil-producers’ (> 6%), accessions of highly productivity of ‘green’ raw materials rich in polyphenols and triterpenoids were also identified. According to their rosmarinic acid content, Greek oregano accessions were classified in three groups; 1) those with significantly high concentration (1640 - 2726 mg 100 g-1 dry weight), 2) those expressing intermediate content (1103 - 1200 mg 100 g-1 dry weight), and 3) the ones with significantly low content (< 873 mg 100 g-1 dry weight). A total of 118 polymorphic alleles were identified using sequence-related amplified polymorphism (SRAPs) and simple sequence repeat (SSRs) markers, while 2 genetic clusters based on a single data matrix with SRAPs and SSRs alleles, were identified. The presence of private bands in some accessions was also observed, which can be used in future breeding programs for germplasm authentication purposes. As a result this study provides a comprehensive knowledge on metabolic and genetic diversity of Greek oregano accessions native to Greece, as well as powerful tools for the selection of starting genetic materials for subsequent breeding studies to create superior cultivars. The multifaceted approach was developed to exploit the genetic resources of Greek oregano in further breeding programs for subsequent selection of genotypes with desired traits