Polypore fungi in the family Ganodermateaceae are mostly considered to be generalist decomposers, associated with the breakdown of dead woody material, or the heartwood of living trees. However, the genus Amauroderma s.lat is associated with tree root infections and butt or root-rot disease, principally in caesalpinoid legumes. Extensive searches in Panama have revealed that Amauroderma infections are entirely restricted to a single host, the canopy tree species Tachigali versicolor, and that fruiting bodies of Amauroderma only emerge when this tree species flowers. This association is especially intriguing because many Tachigali species, including T. versicolor, are monocarpic, flowering only once before dying. The distinction between the specificity of the Amauroderma-Tachigali association compared to other polypores raises questions about the timing of infection, the parasitic or endophytic lifestyle of the fungus, and its evolutionary relationship with monocarpic and non-monocarpic Tachigali hosts (~80 species across the Amazon basin). To date, progress in delimiting this relationship has been hindered by another feature of Tachigali biology: trees flower synchronously, often associated with El Niño events. Currently a mass flowering of Tachigali is underway in Panama, Peru and Colombia. We anticipate Tachigali trees will also flower in the upcoming dry season later this year in French Guiana. In addition to the Amauroderma association, Tachigali has another notable feature of its roots. It is a member of a mostly non-N fixing clade of legumes, yet associates with a unique clade of Bradyrhizobium N-fixing bacteria distinct from those found in nodulated mimosoid legumes.

Here we propose to survey host tree associations of Amauroderma among tagged and identified trees in permanent forest plots at Nouragues and Paracou. This will complement additional surveys this year planned for Panama (Barro Colorado), Colombia (Amacayacu) and Peru (Madre de Dios) targeting 17 Tachigali species. We will (i) collect Amauroderma fruiting bodies for Sanger sequencing to determine host range and to build a fungal phylogeny and analyze concordance with a Tachigali phylogeny; (ii) collect seed tissue, seedling tissue, and root and stem tissue from flowering and non-reproductive adults for metagenomic sequencing to determine when Amauroderma infection occurs and to characterize Tachigali root Bradyrhizobium and fungal communities; (iii) use carbon and nitrogen isotope analysis to compare the nutritional mode of Amauroderma to that of saprotrophic fungi present on the same trees. Collectively, these data will reveal whether Amauroderma forms prolonged asymptomatic infections in its host, whether Amauroderma are root parasites, whether infections are restricted to monocarpic species of Tachigali, and whether host, fungi, and bacterial N-fixing symbionts have co-evolved across an existing Tachigali phylogeny.