Assessment of Relationship between Effective Traits on Yield and Citral Content of Lemon Balm (Melissa officinalis L.) Populations using Path Analysis

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Lemon balm ( Melissa officinalis L.) is one of the most important medicinal plants in the world trade that contains essential oils and has many applications in drug and flavoring industrials. In this study the relationships between the effective characters on yield, citral content and morphological traits in nine Iranian lemon balm populations and two populations from Germany and Japan were assessed in field conditions. Path analysis was performed on plant characters of 11 lemon balm populations to determine for essential oils yield, the direct and indirect effects of the following traits: essential oils percentage, citral content, plant height, number of tiller, chlorophyll index, number of nodes, stem diameter, leaf length, leaf width, leaf area index (LAI), total fresh weight, fresh weight of leaves in the lower a second of plant (L1f), fresh weight of leaves in the upper a second of plant (L2f), fresh weight of stems in the lower a second of plant (S1f), fresh weight of stems in the upper a second of plant (S2f), total dry weight, dry weight of leaves in the lower a second of plant (L1d), dry weight of leaves in the upper a second of plant (L2d), dry weight of stems in the lower a second of plant (S1d), dry weight of stems in the upper a second of plant (S2d) and dry/fresh weight ratio. Essential oils yield was significantly correlated with the leaf width, essential oils percentage and citral content. The result of path analysis showed that essential oil percentage and leaf width had the highest and lowest direct effect on essential oil yield in the assessed populations, respectively. Using these results, breeders can collect plants with high shoot yield, in order to select plants with high essential oil.