Wood decay fungi associated with standing and failed conifer and broadleaf trees as detected through molecular assays: inferences on their host preference and their role on tree stability

In this paper we report the results of a long lasting research based either on the application of Multiplex PCRs previously developed for the detection of the most harmful or widespread wood decay agents of both conifers and broadleaves or on DNA sequencing of the fungal ribosomal ITS region. Molecular diagnosis was performed on DNA extracted directly from wood samples collected since 2006 from both standing and failed trees. A total of 685 broadleaf and 117 conifer standing trees belonging to 13 and 9 species, respectively, were sampled, while failed trees included 39 broadleaves (from 13 species) and 19 conifers (from 6 species). The most frequent fungus detected in standing broadleaves was Armillaria spp. (14% of trees), followed by Ganoderma resinaceum (5% of trees) and Perennipora fraxinea (4% of trees), while in conifers the frequency of Armillaria spp. (13% of trees) was higher than that of Fuscoporia torulosa (7% of trees) and Phaeolus schweinitzii (6% of trees). The frequency of each fungal species greatly varied depending on the host species, suggesting relevant degrees of host preference. The percentage of failed trees colonized by wood destroying fungi differed significantly between conifers and broadleaves (58% vs 85%; Fisher test, P<0.05), suggesting that wood decay fungi may play a more prominent role as factors of tree instability in the case of broadleaves. Exceptions might be represented by Platanus spp. (60% of failed trees colonized by wood decay fungi) and Pinus pinea (88% of trees colonized). The most frequent fungi associated with tree failures varied based on the host species: P. schweinitzii for P. pinea, Armillaria spp. for Cedrus spp. and Populus nigra, Ganoderma adspersum for Aesculus hippocastanum and Fagus sylvatica, and G. resinaceum for Platanus spp.