The Genetic Diversity and Genetic Structure of the Germplasm Resources of the Medicinal Orchid Plant Habenaria dentata.

Habenaria dentata has medicinal and ornamental value, but the number of wild populations is decreasing dramatically. Thus, conducting research on its genetic diversity and structure is necessary to provide a basis for its conservation. This study aimed to explore the genetic diversity of the wild plant H. dentata and protect and optimize its wild resources. The genetic diversity of 133 samples from six wild populations of H. dentata was analyzed using Inter Simple Sequence Repeat molecular markers to provide a scientific basis for the screening of improved germplasm resources. The results showed that the average number of alleles was 1.765, the average number of effective alleles was 1.424, the average Nei's gene diversity index was 0.252, the average Shannon diversity index was 0.381, and the average percentage of polymorphic loci was 76.499%. The variation within the populations was 77.34%, and the variation between the populations was 22.66%. The gene flow was 1.705, which was greater than 1. The results of the cluster analysis showed that the six populations were mainly divided into four clusters and were not classified according to their geographical location. There was no significant correlation between the geographical location and genetic distance between the populations (r = 0.557, p > 0.05). The genetic diversity of H. dentata is high. Among the six wild populations, the genetic diversity of the Mulun population was the highest and this population can be used as a key protection unit. The study on the genetic diversity of H. dentata can not only reveal the reasons for the decrease in the number of individuals in the population to a certain extent, and put forward the protection strategy, but also provide a scientific basis for the breeding of excellent seed resources.

Genomic evidence reveals high genetic diversity in a narrowly distributed species and natural hybridization risk with a widespread species in the genus Geodorum.

BACKGROUND: Understanding genetic diversity is a core issue in conservation genetics. However, previous genetic diversity evaluations of narrowly distributed species have rarely used closely related widespread species as a reference. Furthermore, identifying natural hybridization signals between narrowly and widely distributed sympatric species is of great importance for the development of species conservation programs. METHODS: In this study, population genotyping by sequencing (GBS) was performed for a narrowly distributed species, Geodorum eulophioides (endemic and endangered in Southwest China), and a widespread species, G. densiflorum. A total of 18,490 high-quality single nucleotide polymorphisms (SNPs) were identified at the whole-genome level. RESULTS: The results showed that the nucleotide diversity and heterozygosity of G. eulophioides were significantly higher than those of G. densiflorum, confirming that narrowly distributed species can still preserve high genetic diversity. Consistent with taxonomic boundaries, all sampled individuals from the two species were divided into two genetic clusters and showed high genetic differentiation between species. However, in a sympatric population, a few G. eulophioides individuals were detected with genetic components from G. densiflorum, suggesting potential interspecific natural hybridization. This hypothesis was supported by Treemix analysis and hand-hybridization trials. Invasion of the habitat of G. eulophioides invasion by G. densiflorum under anthropogenic disturbance may be the main factor causing interspecific hybridization. CONCLUSIONS: Therefore, reducing or avoiding habitat disturbance is a key measure to protect the G. eulophioides populations. This study provides valuable information for future conservation programs for narrowly distributed species.

Aphyllorchis yachangensis (Orchidaceae), a new holomycotrophic orchid from China.

Aphyllorchis yachangensis, a new holomycotrophic orchid from Guangxi, southern China is described and illustrated here. This new species is similar to A. caudata but differs from the latter mainly by the sepals acute at the apex, the hypochile with 2 smaller and semicircular wings, the epichile adaxially smooth, acute, the lateral lobes triangular-ovate and the column clavate.

Specificity and preference of mycorrhizal associations in two species of the genus Dendrobium (Orchidaceae).

Dendrobium is a large genus of tropical epiphytic orchids. Some members of this genus are in danger of extinction across China. To investigate orchid mycorrhizal associations of the genus Dendrobium, plants from two Dendrobium species (Dendrobium officinale and Dendrobium fimbriatum) were collected from two habitats in Guangxi Province, China, and clone libraries were constructed to identify the mycorrhizal fungi of individual plants. A low and high degree of specificity was observed in D. officinale and D. fimbriatum, respectively. Phylogenetic analysis revealed that the majority of Dendrobium mycorrhizal fungi are members of the Tulasnellaceae, but, in some plants, members of the Ceratobasidiaceae and Pluteaceae were also found. In D. officinale, individual plants associated with more than three fungi simultaneously, and, in some cases, associations with five fungi at the same time. One fungus was shared by individual plants of D. officinale collected from the two habitats. In D. fimbriatum, only one fungal partner was found in each population, and this fungus differed between populations. The two species of Dendrobium sampled from the same habitat did not share any fungal taxa. These results provide valuable information for conservation of these orchid species.

The pollination of a self-incompatible, food-mimic orchid, Coelogyne fimbriata (Orchidaceae), by female Vespula wasps.

BACKGROUND AND AIMS: The study of specialized interactions between species is crucial to our understanding of processes in evolutionary ecology due to their profound effect on life cycles and diversification. Obligate pollination by a single wasp species is rare in Orchidaceae except in species with sexually deceptive flowers that are pollinated exclusively by male insects. The object of this study was to document pollination of the food-deceptive flowers of Coelogyne fimbriata, a species pollinated exclusively by female wasps. METHODS: Field observations and experiments were conducted in two populations of C. fimbriata. Floral phenology was recorded, and functional floral architecture was measured. Insect visitors to flowers were observed from 2005 to 2007. Bioassay experiments were conducted to check whether the floral odour attracted pollinators. Natural (insect-mediated) rates of pollinarium removal, pollinium deposition on stigmas, and fruit set were recorded. To determine the importance of cross-pollination, the breeding system was assessed via controlled, hand-pollination experiments. KEY RESULTS: Two populations of C. fimbriata with fragrant, nectarless flowers are pollinated by females of the same Vespula species (Vespidae, Hymenoptera). Experiments on wasps show that they crawl towards the source of the odour. The flowering period appears to coincide with an annual peak in Vespula colony expansion when additional workers forage for carbohydrates. Rates of pollinarium removal (0.069-0.918) and pollinium deposition on stigmas (0.025-0.695) are extremely variable. However, fruit set in C. fimbriata is always low (0.014-0.069) and appears to be based on self-incompatibility coupled with intraclonal (geitonogamous) deposition of pollinia. CONCLUSIONS: Coelogyne fimbriata and Steveniella satyrioides are now the only orchid species known to have food-deceptive flowers that are pollinated exclusively by eusocial, worker wasps. In C. fimbriata, floral odour appears to be the major attractant. Sub-populations may go through flowering seasons when pollinators are abundant or infrequent, but fruit set always remains low because the obligate pollinator does not often appear to transfer pollinaria between intercompatible genets.