Genetic, chemical and agro-morphological evaluation of the medicinal plant Origanum vulgare L. for marker assisted improvement of pharmaceutical quality
Most of commercially used medicinal and aromatic plant species are collected from the wild flora. By bringing medicinal herbs into cultivation, conventional and biotechnological plant breeding techniques can be applied to improve herbage yield and plant uniformity as well as pharmaceutical properties. Origanum vulgare L. (oregano) is a perennial aromatic herb belonging to the family Lamiaceae used as medicinal plant because of the essential oil produced in the aerial parts.The present study was basically designed to assess the genetic diversity of the oregano germplasm based on molecular markers, chemical compounds of essential oils and agro-morphological traits. The ultimate goal of our research was to use trait-to-trait correlation and marker-trait association analysis to identify morphologic characters and potential molecular markers for future use for indirect screening and marker-assisted selection, respectively. The other objective of this thesis was to identify the most appropriate soil moisture regime and nitrogen fertilization for the plant growth to obtain a high level of the essential oil content.Twelve traits related to agronomic and morphological characteristics were measured. Components in the essential oils were identified by GC-MS and 18 major compounds of 60 identified constituents, were investigated. A total of 477 molecular polymorphisms including 214 AFLP (Amplified Fragment Length Polymorphisms) and 263 SAMPL (Selectively Amplified Microsatellite Polymorphic Loci) were used for genotyping. Associations between traits of interest and genetic markers were tested using five methods including three general linear models (GLM) and two unified mixed linear model (MLM). In this study, the relative efficiencies of two PCR-based marker approaches, AFLP and SAMPL, were also compared for surveying genetic diversity and subspecies discrimination among 42 oregano accessions.The results of the greenhouse experiment with three populations of oregano cultivated in Germany (O. vulgare var. creticum, O. vulgare ssp. hirtum and O. vulgare var. samothrake) indicated that water deficiency after beginning of blooming can induce an increase in essential oil content and thus result in higher quality of oregano herbage and higher water use efficiency of oregano plants. This finding may give applicable advice to commercial farmers and researches for better management and proper allocate of water resources for cultivation of oregano in arid and semi-arid areas.According to the results of diversity surveying in oregano germplasm, cluster analysis, population inference and principal component analysis (PCA) revealed a broad variation among accessions. A relatively high correlation between chemotypic patterns and genetic markers was identified while a lower correlation was found between the agro-morphological and genetic matrices. The results also showed that SAMPL marker system seems to be more effective than AFLP for studies on intraspecific diversity and relationships among O. vulgare subspecies and also for marker-trait association analyses. Considering the results of analyses of trait-to-trait correlations and marker-trait associations, we can conclude that stem diameter, an easily measurable morphological trait, could be considered for indirect selection and three identified molecular markers, AFLP-2_31, SAMPL-1_18 and SAMPL-3_60 may be included in marker-assisted programmes to improve breeding efficiency of pharmaceutical properties. These findings can be very applicable for domestication and breeding strategies in Origanum vulgare and also for management of its genetic resources.
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