Correlation between the Agronomical Characteristics and Essential Oil Content of Origanum onites L. and Melissa officinalis L.

Due to their widespread use in the pharmaceutical, cosmetic and food industries, medicinal and aromatic plants have gained importance with an increasing number of studies being conducted concerning the yield and quality characteristics of these plants. In breeding studies, selection is successful when there a correlation is established between the essential oil content, composition, and morphological and agronomic characteristics. The aim of this study was to address the correlation between the yield and quality of medicinal and aromatic plants to present a different perspective for breeding studies. Therefore, in this study, the relationship among the characteristics and the essential oil content of Izmir oregano (Origanum onites L.) and lemon balm (Melissa officinalis L.) plants were investigated, and correlation and path analyses were performed. There was a significant negative correlation between the essential oil content and fresh herb (-0.279*), dry herb (-0.281*), and dry stem yield (-0.283*) of Izmir oregano. However, no significant correlation was found between the essential oil content and these agronomic characteristics in lemon balm. Fresh herb yield had a significant positive correlation with dry herb (0.661**), dry leaf (0.690**), and dry stem yield (0.610**). Dry herb yield was significantly and positively correlated with dry leaf (0.510*) and dry stem (0.461*) yields. A significant positive correlation was also observed between dry leaf and dry stem (0.688**) yields. According to the results of the path analysis, while the maximum negative effect on the essential oil content of Izmir oregano was provided by dry herb (-48.05%) yield, the highest direct positive effect belonged to dry leaf (21.69%) and dry stem (15.13%) yields. Dry leaf yield (-51.61%) and plant height (-45.71%) were the parameters that had the highest direct negative effect on the essential oil content of lemon balm while fresh herb (33.50%) and dry herb (30.27%) yields were the source of the highest direct positive effect.