Genetic diversity assessment of Hopea hainanensis in Hainan Island

Low genetic diversity and weak population structure of Albizia odoratissima on Hainan Island

BACKGROUND

The increasing demand for wood owing to societal development has highlighted the potential of Albizia odoratissima, a valuable timber species, to address significant timber shortages in China. However, the lack of effective genetic and genomic resources has limited the development and utilization of this species.

RESULTS

In this study, we utilised 95.3 Gb of HiFi reads to assemble a draft genome of A. odoratissima, resulting in a genome size of 788 Mb, comprising 511 contigs. We conducted whole-genome resequencing on 106 individuals from 7 populations on Hainan Island to explore these resources. Our analysis identified 498,308 high-quality single nucleotide polymorphisms, which were used to assess the genetic diversity, structure, and demographic history of A. odoratissima on Hainan Island. The results indicated that the genetic diversity of A. odoratissima on Hainan Island is relatively low (observed heterozygosity = 0.189, expected heterozygosity = 0.189, genetic diversity = 1.319 × 10-4) with minimal genetic differentiation (Fst = 0.0151) among the seven populations. Furthermore, molecular variance, principal coordinate analysis, neighbour-joining tree analysis, and genetic structure analysis revealed a shallow population structure. The linkage disequilibrium (LD) decay ranged from 11.4 kb for Jianfengling (JFL) to 39.2 kb for Wuzhishan (WZS). LD decay, demographic history, and Tajima's D analyses indicated that the WZS population has experienced a bottleneck effect.

CONCLUSIONS

This study offers new insights into the genetic diversity and population structure of A. odoratissima on Hainan Island, providing a foundation for future resource utilization and genetic improvement strategies for this species.

Genetic diversity assessment of clonal plant Rosa persica in China

Rosa persica is considered a clonal plant because it is mainly propagated by clonal growth. Due to environmental degradation and habitat devastation, R. persica has been listed as a national second-class protected plant in China. However, the absence of research on wild populations of R. persica has impeded progress in formulating efficient conservation strategies. In this study, we investigated the clonal dispersal distance of R. persica to accurately determine the genetic diversity and population structure of the wild population in Xinjiang. We suggested that 20 m was the threshold distance with which to distinguish between different genets of plants. Based on this, we collated sequencing data from a total of 70 different genets of plants from 117 test samples. Eight populations of R. persica were primarily categorized into three subgroups: BL (Bole), TC (Tacheng) and CG (Changji). Of these, the CG subgroup exhibited the most genetic diversity. This research is the first to illustrates the clonal dispersal distance of R. persica, thus providing valuable reference guidelines for understanding the reproductive characteristics of clonal plants. In addition, the genetic diversity of R. persica provides a theoretical foundation for the formulation of conservation policies.

Conservation genomic study of Hopea hainanensis (Dipterocarpaceae), an endangered tree with extremely small populations on Hainan Island, China

Introduction

Hopea hainanensis Merrill & Chun is considered a keystone and indicator species in the tropical lowland rainforests of Hainan Island. Owing to its high-quality timber, H. hainanensis has been heavily exploited, leading to its classification as a first-class national protected plant in China and a plant species with extremely small populations (PSESPs).

Methods

This study analyzed genome-wide single nucleotide polymorphisms obtained through restriction site-associated DNA sequencing from 78 adult trees across 10 H. hainanensis populations on Hainan Island.

Results and discussion

The nucleotide diversity of the sampled populations ranged from 0.00096 to 0.00138, which is lower than that observed in several other PSESPs and endangered tree species. Bayesian unsupervised clustering, principal component analysis, and neighbor-joining tree reconstruction identified three to five genetic clusters in H. hainanensis, most of which were geographically widespread and shared by multiple populations. Demographic history analysis based on pooled samples indicated that the decline in the H. hainanensis population began approximately 20,000 years ago, starting from an ancestral population size of approximately 10,000 individuals. The reduction in population size accelerated approximately 4,000 years ago and has continued to the present, resulting in a severely reduced population on Hainan Island. Intensified genetic drift in small and isolated H. hainanensis populations may contribute to moderate differentiation between some of them, as revealed by pairwise F st. In conclusion, our conservation genomic study confirms a severe population decline and an extremely low level of nucleotide variation in H. hainanensis on Hainan Island. These findings provide critical insights for the sustainable management and genetic restoration of H. hainanensis on Hainan Island.

Assessing genetic diversity in critically endangered Chieniodendron hainanense populations within fragmented habitats in Hainan

Habitat fragmentation has led to a reduction in the geographic distribution of species, making small populations vulnerable to extinction due to environmental, demographic, and genetic factors. The wild plant Chieniodendron hainanense, a species with extremely small populations, is currently facing endangerment and thus requires urgent conservation efforts. Understanding its genetic diversity is essential for uncovering the underlying mechanisms of its vulnerability and for developing effective conservation strategies. In our study, we analyzed 35 specimens from six different populations of C. hainanense using genotyping-by-sequencing (GBS) and single nucleotide polymorphism (SNP) methodologies. Our findings indicate that C. hainanense has limited genetic diversity. The observed heterozygosity across the populations ranged from 10.79 to 14.55%, with an average of 13.15%. We categorized the six populations of C. hainanense into two distinct groups: (1) Diaoluoshan and Baishaling, and (2) Wuzhishan, Huishan, Bawangling, and Jianfengling. The genetic differentiation among these populations was found to be relatively weak. The observed loss of diversity is likely a result of the effects of natural selection.

Genome-wide diversity evaluation and core germplasm extraction in ex situ conservation: A case of golden Camellia tunghinensis

Whether ex situ populations constructed in the limited nursery resources of botanical gardens can preserve enough genetic diversity of endangered plants in the wild remains uncertain. Here, a case study was conducted with Camellia tunghinensis, which is one of the species with the lowest natural distribution area in the sect. Chrysantha (golden camellia) of the family Theaceae. We investigated the genetic diversity and population structure of 229 samples from wild and ex situ populations using genotyping by sequencing (GBS). Core germplasm was constructed from these samples. The results showed that wild C. tunghinensis exhibited high genetic diversity, with observed heterozygosity of 0.257-0.293 and expected heterozygosity of 0.247-0.262. Compared with wild populations, the genetic diversity of ex situ populations established by transplanting wild seedlings was close to or even higher. However, the genetic diversity of those established by seed or cuttings of a few superior trees was lower. The Admixture analysis revealed that the structure of the ex situ populations derived from seeds and cuttings was relatively simple compared with the ex situ populations derived from transplanted wild seedlings and wild populations. These results suggested that direct transplanting of wild seedlings was more conducive to preserving the genetic diversity of endangered plants in the wild. In addition, wild populations demonstrated a small differentiation (mean F ST = 0.044) among themselves, possibly due to long-term and frequent gene flow between the wild populations. In contrast, moderate differentiation (mean F ST > 0.05) was detected among ex situ populations and between ex situ and wild populations. This may be the combined result of the absence of gene flow pathways and strong selection pressure in various ex situ environments. Finally, 77 core germplasms were extracted from 229, likely representing the genetic diversity of C. tunghinensis. This study provides future strategies for the ex situ conservation and management of the golden camellia species and other rare and endangered plants.