Variation at a chloroplast minisatellite locus reveals the signature of habitat fragmentation and genetic bottlenecks in the rare orchid Anacamptis palustris (Orchidaceae)

The structure and diversity of bacteria and fungi in the roots and rhizosphere soil of three different species of Geodorum

Shepherd's crook (Geodorum) is a genus of protected orchids that are valuable both medicinally and ornamentally. Geodorum eulophioides (GE) is an endangered and narrowly distributed species, and Geodorum densiflorum (GD) and Geodorum attenuatum (GA) are widespread species. The growth of orchids depend on microorganisms. However, there are few studies on the microbial structure in Geodorum, and little is known about the roles of microorganisms in the endangered mechanism of G. eulophioides. This study analyzed the structure and composition of bacterial and fungal communities in the roots and rhizosphere soil of GE, GD, and GA. The results showed that Delftia, Bordetella and norank_f_Xanthobacteraceae were the dominant bacteria in the roots of Geodorum, while norank_f_Xanthobacteraceae, Gaiella and norank_f_norank_o_Gaiellales were the dominant bacteria in the rhizosphere soil of Geodorum. In the roots, the proportion of Mycobacterium in GD_roadside was higher than that in GD_understory, on the contrary, the proportion of Fusarium, Delftia and Bordetella in GD_roadside was lower than that in GD_understory. Compared with the GD_understory, the roots of GD_roadside had lower microbial diversity. In the endangered species GE, Russula was the primary fungus in the roots and rhizosphere soil, with fungal diversity lower than in the more widespread species. Among the widespread species, the dominant fungal genera in the roots and rhizosphere soil were Neocosmospora, Fusarium and Coprinopsis. This study enhances our understanding of microbial composition and diversity, providing fundamental information for future research on microbial contributions to plant growth and ecosystem function in Geodorum.

Seed banking of terrestrial orchids: evaluation of seed quality in Anacamptis following 4-year dry storage

Good-quality dry seeds of some orchids have the potential to survive for decades under conventional seed bank conditions, but further research is needed to fill existing gaps in knowledge regarding seed behaviour under long-term dry storage. The objectives of this study were to evaluate germination ability on two asymbiotic culture media with different nitrogen source; to assess seed desiccation tolerance needed for the storage at sub-zero temperatures; and to study the effects of dry storage at low temperature. Asymbiotic seed germination tests of four Anacamptis species were carried out to evaluate the effects of different culture media, dehydration and dry storage on germination ability. Viability of 4-year-stored seeds was assessed by means of the tetrazolium test. Generalised linear model (GLM) analysis detected significant effects (P < 0.01) of the species, medium and storage time on total germination, while dehydration did not significantly affect it. Except for A. palustris, germination percentage was minimum after 1-month storage and increased with longer storage periods. Tetrazolium viability tests detected high percentages of viable seed (>90%) following 4-year storage in three out of four species. Seeds of the four Anacamptis species proved to be desiccation tolerant and have orthodox storage behaviour. The consequence of these findings is of interest to practical conservation approaches for orchids in seed-banking. The results highlight the importance of multiple assessments of seed quality, both viability and germination, to understand seed storage behaviour.

Collecting near mature and immature orchid seeds for ex situ conservation: 'in vitro collecting' as a case study

BACKGROUND

Lack of phenological information and efficient collecting methods are considered impediments for orchid seed collecting. This leads to opportunistic collecting as part of general seed collecting schedules that may last few weeks especially in remote areas. The study explored the feasibility of collecting near mature and immature seeds to support conservation action plans. Mature, near mature and immature seeds of orchids were collected from the wild in the Central Highlands of Madagascar (CHM). Seed capsules were collected in sterile culture medium in the wild, to prevent deterioration of seeds inside the capsule after collecting, later to be cultured under laboratory conditions.

RESULTS

Seed capsules collected by the in vitro collecting (IVC) method were kept in very good condition for up to 4 weeks before germination under in vitro conditions. Significantly faster and higher germination rate (p < 0.001) than mature seeds was observed in a number of taxa collected during a 3 year-long study. In some taxa even immature seeds, with no apparent sign of testa covering the embryo, germinated following IVC where mature seeds failed to germinate.

CONCLUSIONS

We propose that IVC method has potential to complement conventional seed collecting by increasing the germplasm that can be used in integrated conservation action plans. Improvements can be made in developing collections for taxa from biodiversity hotspots and remote areas where collecting requires considerable resources. This method can further be used on a wider selection of plants from different geographic areas and on embryo rescue programmes for economically important plants.

Reproductive patterns, genetic diversity and inbreeding depression in two closely related Jumellea species with contrasting patterns of commonness and distribution

BACKGROUNDS AND AIMS

Theory predicts that the long-term persistence of plant populations exposed to size reduction can be threatened by a loss of genetic diversity and increased inbreeding. However, several life-history and ecological traits can influence the response to population size reduction. The reproductive patterns, levels of genetic diversity and magnitude of inbreeding depression of the rare and fragmented Jumellea fragrans and of its widespread congener J. rossii were studied. The aim was to evaluate the effects of over-collection and fragmentation on J. fragrans and to enhance our knowledge of the biology and ecology of the two species, used for their aromatic and medicinal properties on Réunion.

METHODS

Hand pollination experiments were conducted to determine the breeding system and to evaluate the potential for inbreeding depression in both species. Nuclear microsatellite markers were used to investigate selfing rates and levels of genetic diversity.

KEY RESULTS

Jumellea rossii revealed a mixed-mating system, and inbreeding depression at the germination stage (δ = 0·66). Levels of genetic diversity were relatively high [allelic richness (AR) = 8·575 and expected heterozygosity (He) = 0·673]. In J. fragrans, selfing rates suggest a mainly outcrossing mating system. Genetic diversity was lower than in J. rossii, but not yet critically low (AR = 4·983 and He = 0·492), probably because of the mainly outcrossing mating system and the relatively high density of individuals in the studied population. Jumellea fragrans did not show inbreeding depression, and it is hypothesized that the population had progressively purged its genetic load during successive fragmentation events.

CONCLUSIONS

Even if the persistence of the J. fragrans population is not threatened in the short term, its genetic diversity has probably been reduced by fragmentation and over-collection. In situ conservation actions for J. fragrans and ex situ cultivation of both species are recommended in order to meet the demand of local people.

Susceptibility of common and rare plant species to the genetic consequences of habitat fragmentation

Small plant populations are more prone to extinction due to the loss of genetic variation through random genetic drift, increased selfing, and mating among related individuals. To date, most researchers dealing with genetic erosion in fragmented plant populations have focused on threatened or rare species. We raise the question whether common plant species are as susceptible to habitat fragmentation as rare species. We conducted a formal meta-analysis of habitat fragmentation studies that reported both population size and population genetic diversity. We estimated the overall weighted mean and variance of the correlation coefficients among four different measures of genetic diversity and plant population size. We then tested whether rarity, mating system, and plant longevity are potential moderators of the relationship between population size and genetic diversity. Mean gene diversity, percent polymorphic loci, and allelic richness across studies were positively and highly significantly correlated with population size, whereas no significant relationship was found between population size and the inbreeding coefficient. Genetic diversity of self-compatible species was less affected by decreasing population size than that of obligate outcrossing and self-compatible but mainly outcrossing species. Longevity did not affect the population genetic response to fragmentation. Our most important finding, however, was that common species were as, or more, susceptible to the population genetic consequences of habitat fragmentation than rare species, even when historically or naturally rare species were excluded from the analysis. These results are dramatic in that many more plant species than previously assumed may be vulnerable to genetic erosion and loss of genetic diversity as a result of ongoing fragmentation processes. This implies that many fragmented habitats have become unable to support plant populations that are large enough to maintain a mutation-drift balance and that occupied habitat fragments have become too isolated to allow sufficient gene flow to enable replenishment of lost alleles.

Chloroplast DNA Inheritance in the Orchid Anacamptis palustris Using Single-Seed Polymerase Chain Reaction

The modality of chloroplast inheritance in orchids has been investigated only in a few species due to the difficulties associated with the analysis of large progeny numbers from experimental crosses. To test chloroplast DNA inheritance in the orchid Anacamptis palustris, we took advantage of the presence of a highly variable minisatellite repeat located in the tRNA(LEU) intron in the chloroplast genome. Seed progeny obtained from experimental crosses between parental individuals carrying different chloroplast DNA (cpDNA) minisatellite repeat numbers were analyzed using a single-seed polymerase chain reaction (PCR) protocol. All examined seeds displayed the maternal cpDNA haplotypes, indicating that cpDNA inheritance is strictly maternal in this Mediterranean orchid species. No evidence for paternal leakage was found. This finding concurs with results obtained from PCR amplifications of pollen massulae that exclude the presence of chloroplast DNA in the pollen tetrads.