Relationships between orchid and fungal biodiversity: Mycorrhizal preferences in Mediterranean orchids

Orchidaceae is one of the most species-rich angiosperm families, and all orchids are fully dependent on fungi for their seed germination and their life cycle. The level of specificity of the association between orchid species and fungi can be related to the number of co-occurring orchid species. To investigate orchid mycorrhizal associations in adult-photosynthetic orchids, 16 Mediterranean orchid species belonging to 4 genera (Anacamptis, Ophrys, Orchis, and Serapias) at 11 different sites were subjected to DNA-based analysis. Eighteen operational taxonomic units representing two fungal families, Tulasnellaceae and Ceratobasidiaceae, were identified. All examined orchid species associated with different mycorrhizal fungi. Interestingly, there was a positive correlation between number of orchid species and number of mycorrhizal. Monospecific populations showed a lower number of fungi, while sympatric populations had a higher number of mycorrhizal fungi. Our results showed that Mediterranean orchid species associated with a higher number of mycorrhizal fungi confirming as photosynthetic orchids are typically generalists toward mycorrhizal fungi. Thus, photosynthetic orchids exhibit low specificity for fungal symbionts showing the potential for opportunistic associations with diverse fungi reducing competition for nutrient. We suggest that these characteristics could confer symbiotic assurance particularly in habitat with resource limitations or prone to stressful conditions.     

Crossing barriers between the unrewarding Mediterranean orchids Serapias vomeracea and Serapias cordigera

Understanding the genetic architecture of admixed hybridizing populations helps in evaluating the nature of species boundaries and the levels of gene exchange between co-occurring species. In the present study, we examined a contact zone between Serapias vomeracea and Serapias cordigera , two unrewarding Mediterranean orchid species with a non-specific pollination strategy. Fruit production and seed viability from interspecific hand-pollination treatments pointed out the weaknesses of post-pollination barriers. The occurrence of hybridization was molecularly confirmed in the genus Serapias for the first time, as parts of plants with a transitional morphology were observed in both alleles of the parental LEAFY intron. Amplified fragment length polymorphism analysis revealed that plants with uncertain morphology and classified as one of the other parental species are actually backcrosses, attesting to an extensive interspecific gene exchange. Overall, the contact zone is more similar to a hybrid zone of Ophrys species, well known for their highly specialized pollination, than to a hybrid zone of unspecialized food-deceptive orchids. Therefore, species boundaries in Serapias are maintained by pre-pollination mechanisms that need to be better investigated. In light of the intriguing similarities between Serapias and Ophrys underlined by the present study, we hypothesize that the emission of floral scents could be involved in the maintenance of species boundaries in Serapias .     

Isolation and characterization of microsatellite loci from the orchid Serapias vomeracea (Orchidaceae) and cross‐priming to other Serapias species

In this paper we describe the isolation and characterization of six polymorphic microsatellite loci from the orchid Serapias vomeracea. This species is widely distributed in the Mediterranean region. Microsatellite loci were isolated from an enriched library and primer pairs were designed for 18 loci. Primer pairs for six loci amplified well and were tested on samples from southern Italy. Levels of genetic variability detected at these six loci are high, with numbers of alleles per locus ranging from 3 to 6, and observed heterozygosity (H_O) ranging from 0.35 to 0.86. All primer pairs tested amplified DNA from four other Serapias species, indicating that the primers are useful for population genetic studies throughout the genus.