DNA barcoding-based assessment of genetic variation in selected Southwest Nigerian medicinal Senna species (Caesalpinoideae: Fabaceae)

Abstract

Senna species in Southwest Nigeria possess significant medicinal and economic potential yet remain underutilized. This study aimed to employ DNA barcoding to characterize twenty Senna accessions and assess their genetic variation. Seeds from twenty accessions comprising six species (S. hirsuta, S. obtusifolia, S. alata, S. siamea, S. acutifolia, and S. occidentalis) were collected from Southwest Nigerian states. Fresh leaf samples underwent DNA extraction, PCR amplification of the psbA-trnH intergenic spacer region, and Sanger sequencing. Molecular analyses using Bioedit, MEGA 11, and NCBI BLAST yielded high-quality DNA sequences (312-414 bp). BLAST searches confirmed species identities with exceptional accuracy. Multiple alignments revealed inter-specific variations and genus-specific conserved regions. Genetic distance analysis showed moderate diversity (0.000-0.074) between species. Base composition analysis revealed characteristic A-T rich patterns: thymine showed highest variance, followed by adenine, while cytosine and guanine exhibited lower variation. Conserved sequences provided molecular evidence of monophyletic relationships within Senna, while base composition variations reflected evolutionary divergence and environmental adaptation. These findings establish a molecular framework for the identification and conservation of Nigerian Senna species, supporting their development for medicinal and agricultural applications.