Morphological and genetic diversity of Thymus atlanticus (ball) Roussine, an endemic species of Morocco

Abstract

Thymus atlanticus is an endemic Moroccan species that occurs in the Atlas Mountains, where it grows in well-drained limestone soils. Fourteen accessions of T. atlanticus collected from different regions of Morocco were examined to clarify their taxonomic identity and assess morphological and genetic variation among the accessions. Fourteen morphological traits (eight qualitative and six quantitative) were evaluated using five replicates per accession. Multiple factor analysis, correlation, and cluster analysis of morphological traits were performed. Genetic diversity was assessed using seven start codon targeted (SCoT) primers to determine the polymorphism information content (PIC), number of polymorphic bands and the percentage of polymorphic loci. The results revealed significant differences in morphological traits among the accessions. The coefficients of variation (CVs) for the six quantitative traits ranged from 7.24% for calyx length to 22.02% for leaf width. Morphological analysis classified the accessions into three groups, whereas genetic analysis clustered them into seven distinct groups. Four SCoT markers (SCoT1, SCoT11, SCoT14, and SCoT15) produced 100% polymorphic bands. The lowest proportion of polymorphic bands (89.28%) recorded for SCoT22 and SCoT30. Molecular analysis provided greater discriminatory power than morphological analysis and partially confirmed the morphological results, indicating that geographically neighboring accessions were generally more similar both morphologically and genetically. Collectively, these results demonstrate that T. atlanticus accessions exhibit considerable morphological and genetic polymorphism. The genetic structure identified among the studied accessions therefore provides a valuable foundation for future conservation, germplasm characterization, and breeding programs.