Genetic diversity of ectomycorrhizal symbionts of Lombardy poplar (Populus nigra L. Cv 'Italica'') grown in a range of environments.

Populus is one of the few tree genera with both ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) associations. Little is known about the factors influencing the composition of mycorrhizal fungal communities associated with poplar trees. The frequent interspecific hybridization of poplars complicates field studies aimed at distinguishing the effects of genetic and environmental factors on mycorrhizal communities. Lombardy poplar (P. nigra L. cv ‘Italica’) is a male clone selected in Lombardy, northern Italy, in the 17th century. Spread by cuttings throughout Europe and the USA it has been cultivated as a street and landscape tree in a wide variety of environments. The genetic similarity of Lombardy poplar trees provides an opportunity to determine the effects of local environmental conditions on the composition of mycorrhizal fungal communities associated with a single tree genotype. We examined mycorrhizae of mature Lombardy poplar trees grown under various soil conditions and subject to various types and levels of anthropogenic pressure in Poland. Fine roots were sampled randomly from the upper soil layer in spring and late summer. ECM and AM colonization of the poplar roots were evaluated using the intersection method after cleaning and staining of the root samples with trypan blue. Ectomycorrhizae were sorted into morphotypes based on their morphological characters. DNA was extracted from individual ectomycorrhizae and the rDNA ITS region of the fungal symbiont was amplified by PCR, cloned and sequenced. Molecular taxonomical identification was accomplished using BLAST analysis against sequences in databases followed by phylogenetic analysis (neighbour joining method) of ITS sequences. Alignment with ITS sequences in various databases showed various species of Tuber, Tomentella and Hebeloma, one species each of Laccaria, Helvella, Paxillus and Thelephora and possibly several other species as well; we obtained a number of sequences with close matches in the EMBL Genbank to ‘uncultivated fungal species’ only. The proportion of ECM and AM colonization and the richness and composition of ECM mycobionts associated with the poplar roots differed between study sites, suggesting an effect of local environmental conditions on mycorrhizal symbiosis