Comparative genetic diversity of the endangered, narrowly endemic Chinese orchid Bulbophyllum tianguii and its widespread congener Bulbophyllum andersonii

Introduction Genetic research on endangered plant species is crucial for formulating effective biodiversity conservation and management strategies. Bulbophyllum tianguii , a rare and endangered orchid species endemic to the karst regions of Southwest China, possesses exceptionally high ornamental value. However, its population genetic structure and evolutionary potential remain largely unexplored. Therefore, this study aimed to comparatively evaluate the genetic diversity and population structure of the narrowly distributed B. tianguii and its widespread congener, Bulbophyllum andersonii . Methods We utilized Genotyping-by-Sequencing (GBS) technology to discover 23,880 highquality single nucleotide polymorphisms (SNPs) across 50 B. tianguii (from seven populations) and 31 B. andersonii (from four populations) individuals. Results The results revealed that the key genetic diversity parameters of B. tianguii populations (Ho = 0.101, He = 0.070, I = 0.088, π = 0.077) were significantly (P < 0.01) lower than those of B. andersonii (Ho = 0.105, He = 0.101, I = 0.183, π = 0.111). Population structure, phylogenetic tree, and Principal Component Analysis (PCA) consistently divided B. tianguii into six subpopulations, whereas B. andersonii comprised two subpopulations and one admixed group. Kinship and gene flow analyses indicated that B. tianguii exhibited weaker intra- and inter-population relatedness, accompanied by higher genetic differentiation (FST = 0.450) and restricted gene flow (proxy Nm = 0.411) compared to B. andersonii (FST = 0.268, proxy Nm = 0.830). Mantel tests confirmed that genetic differentiation was not significantly correlated with geographic distance for either species (P < 0.05). Discussion Despite the limitations of lacking a reference genome and uneven sampling sizes, these findings suggest that B. tianguii is characterized by dangerously low genetic diversity. To preserve its gene pool, future conservation should prioritize in situ protection and careful reintroduction, while monitoring the potential risks of outbreeding depression.