Assessing Phenotypic Diversity and Population-Level Differentiation in Laurus nobilis L. Seedlings from the Southwestern Black Sea Region

Abstract

Bay laurel (Laurus nobilis L., Lauraceae) is an economically and ecologically important non-timber forest product widely distributed across Mediterranean and sub-Mediterranean ecosystems. This study assessed phenotypic variation in two-year-old seedlings originating from six natural populations in the Southwestern Black Sea Region. Seedlings were grown under uniform open-field nursery conditions and evaluated using fourteen phenotypic and quality-related traits, including growth parameters, biomass components, and composite seedling quality indices. Univariate and multivariate analyses revealed significant population-level differentiation and supported the emergence of two well‑defined distinct phenotypic groups. The first group exhibited higher biomass accumulation, larger root collar diameter, and more balanced quality index values, indicating stronger structural development and superior seedling quality. In contrast, the second group showed lower biomass production and higher slenderness, reflecting a more limited growth pattern. Mantel tests revealed moderate correlations between phenotypic distances and both geographic and environmental distances; however, these relationships were not statistically significant, suggesting that spatial and environmental gradients alone do not fully account for the observed phenotypic structure. Our results highlight the critical influence of population origin in shaping seedling morphology and quality under uniform nursery conditions. These findings provide a scientific basis for provenance-based seed source selection and contribute to sustainable cultivation, breeding, and conservation strategies for bay laurel, with practical implications for horticulture and urban forestry.