Evidence of Zelkova carpinifolia as a potential host of Tuber uncinatum from the Quaternary of Hyrcanian temperate forests

Abstract Tuber uncinatum (Tuberaceae, Pezizales) is a commercially important ectomycorrhizal (EcM) fungal species associated with many deciduous EcM host species belonging to the Fagales lineage. Because of its host multiplicity among deciduous species, we hypothesized that it might associate with other plant lineages of Rosids as the most recent common ancestral of the ectomycorrhizae (MRCA-EcM) of Ulmaceae radiated preceding Fagaceae. The samples (host plant specimens, fungal ascomata, and soil) were from homogeneous Caucasian elm populations of the Hyrcanian temperate forests of Iran. Diagnosing the host plant was performed by using available botanical sources. The EcM symbiosis evidence and EcMF identity were illustrated by surveying gleba, spore shape, and EcM root anatomy using SEM, light, and stereo-microscopy, followed by molecular analysis. The micrographs obtained from root examination demonstrated the Hartig net penetration among cortical and epidermal cells and the presence of mantle as the EcM sheath. This study supports the EcM symbiosis of T. uncinatum with Zelkova carpinifolia from the Quaternary period in the Hyrcanian temperate forests.