Study on genetic diversity between Origanum L. species based on genome size and ISSR markers

The genus Origanum has the complex taxonomy and extensive genetic variation between species, mainly due to the presence of the significant morphological differences within plants and natural hybridization, even among distantly related species. This genus includes numerous species, subspecies, varieties and hybrids, what makes their characterization very complicated. Moreover, the existence of a large number of synonymous names makes the correct identification difficult. High degree of heterogeneity causes, that a potential for utilization of oregano has not been fully explored yet. Therefore, genome size and ISSR markers can be applied for identification and characterization of species from the Origanum genus. Genome size estimation revealed, that all Origanum species possessed very small genomes. The nuclear DNA content ranged from 1.45 pg/2C (O. vulgare) to 1.73 pg/2C (O. majorana). This is the first time the genome size have been estimated in O. heracleoticum, O. majorana, O. vulgare ssp. gracile, O. vulgare ssp. hirtum and O. vulgare ssp. vulgare. Based on the 2C-values it was possible to distinguish O. majorana from O. syriacum. For the discrimination of all accessions of Origanum genus, the ISSR markers were applied. Using primers: (GACA)(4)A, and (AG)(8)YA, it was possible to identify and distinguish species and subspecies. The relationships within tested accessions reflected by genetic distance estimation and dendrogram construction revealed the existence of two main clusters. The first cluster grouped all the accessions of O. vulgare, whereas two species, O. majorana and O. syriacum, were grouped into second cluster. The identification system composed of flow cytometry and ISSR-PCR technique demonstrated to be useful for genotypes in the Origanum genus.