Genetic Diversity of Siamese Rosewood <em>Dalbergia cochinchinensis</em> Pierre in Thailand: Insights from Chloroplast and Nuclear DNA Analysis

Siamese rosewood (Dalbergia cochinchinensis Pierre) is a highly valuable economic tree species in Thailand. This study investigated genetic diversity across 72 tree samples from 17 Thai locations using two genetic markers: the chloroplast maturase K (matK) gene and the nuclear internal transcribed spacer (ITS) region, which includes ITS1, 5.8S ribosomal RNA gene, and ITS2. Analysis of 48 matK and 65 ITS sequences revealed 34 (DcM1–DcM34) and 31 (DcI1–DcI31) haplotypes, respectively. The Saraburi province haplotype DcM10 exhibited the highest genetic divergence, differing by 25 mutational steps from other haplotypes. Phylogenetic analysis incorporating GenBank sequences from other Dalbergia species showed that matK sequences separated D. cochinchinensis into two distinct clades: Clade A comprising most Thai samples, and Clade B containing Saraburi samples grouped with sequences from Laos and Cambodia. In contrast, ITS analysis revealed a single monophyletic group. These findings have important applications for conservation strategies, particularly in prioritizing the genetically distinct Saraburi population for protection, and can inform breeding programs to maintain genetic diversity. Additionally, the identified genetic markers could be developed into tools for timber authentication to combat illegal logging, while the revealed population structure can guide reforestation efforts and international conservation collaboration with Laos and Cambodia.