Ectomycorrhizas are mutualistic associations, which concern more than 2,000 plant species. Some tropical and subtropical forests are dominated by ectomycorrhizal (ECM) trees, suggesting a key role of these symbioses in the functioning of tropical forest ecosystems. Yet, studies on ECM fungi are nearly exclusively focusing on temperate and boreal forests. This leaves tropical ECM symbiosis poorly documented, thus greatly limiting our understanding of their contribution to tropical ecology. The reason for such a caveat is at least partly technical since investigations on tropical ECM fungi rapidly face a species recognition problem. Indeed, morphological characters of ectomycorrhizas are usually not sufficient for species recognition, especially in tropical habitats where many species coexist but remain poorly known, though not totally unknown. In such a context, molecular tools that were developed for several organisms during the last decades have also proved to be of great help for ECM fungi systematic, and hence ECM diversity assessment and ecology.
We illustrate the potential use of such molecular tools through two interconnected applications: (1) ECM fungi systematics and diversity assessment in tropical rainforests and (2) the spatial distribution of Russula sp. foetentinae genets in a study plot located in the Western Ghâts primary rainforest (India). 1.
To evaluate species composition, phylogenetic analyses based on a fragment of the mitochondrial large subunit rRNA gene were used to type 140 sporocarps and 54 ectomycorrhizas from African and Indian tropical rainforests. Despite differences in vegetation types dominated by Dipterocarpaceae in India, and Caesalpiniaceae and Euphorbiaceae in Guinea, Russulaceae and Amanitaceae were the most diverse families in both places.
2.
On the basis of our species-specific identifications, we then focused on the spatial delimitation of genets of the dominant Russula species (Russula sp. foetentinae) mapped on a 7,700 m² study plot located in India. The genetic structure of this species was further estimated using Inter-Simple Sequence Repeats (ISSR) markers, thus providing valuable insights into the ratio of vegetative versus sexual reproduction. Our results provide preliminary insights into taxonomic diversity, and ECM fungi spatial distribution in tropical rainforest ecosystems, which appear to be as diverse as in temperate and boreal ones.