Exudate flavonoids and their distribution among the plant kingdom have been comprehensive studied by Prof. Eckhard Wollenweber and the followers of this approach for analysis. In addition to being taxonomically important, these compounds have important ecological functions due to their location on the surface on plant. Exudate flavonoids often are defined as a surface, external and lipophilic. Besides flavonoid aglycones in the exudate are contained also terpenes, fatty alcohols and acids, alkanes, phenolic acids. Origanum species are valuable medicinal and culinary herbs, more that their biocidal activity is very important in the last decades. The results of the research on allelopathic interactions are scientific basis for selection of plant products with biocidal properties. The first substances involved in these interactions in nature are the exudate (surface) compounds.In the present study, acetone exudates of ten samples of Origanum species were comparatively analyzed by GC/MS and HPTLC. Plant material of Origanum dictamnus L., Origanum vulgare L. and Origanum vulgare subsp. hirtum (Greek oregano) as the latter taxa was represented by 8 patterns with different origin were studied. Flavonoid aglycones, mono- di- triterpenes, fatty acids and alcohols, alkanes, phenolic acids and derivatives were identified. Methylated derivatives of flavones – apigenin and luteolin were identified as the most common flavonoid aglycones. The most complex flavonoid profile was detected for O. vulgare ssp hirtum samples. A few differences in the flavonoid profiles of O. vulgare ssp hirtum from different origin of were found. Carvacrol (monoterpene phenol) was determined as main component of Origanum vulgare subsp. hirtum samples, in O. dictamnus exudate sesquiterpenes were detected in addition whereas in O. vulgaris exudate long-chain fatty alcohol and alkanes were found as abundant compounds. Differences observed between studied taxa as well as among the examined samples of O. vulgare ssp hirtum were discussed. The data obtained complement the knowledge of the distribution and role of exudate compounds.

Acknowledgements: This research was supported by the Bulgarian National Science Fund, Bulgarian Ministry of Education and Science (Grant DN 16/2, 11.12.2017).