Analysis of genotypic diversity provides a first glimpse on the patterns of spread of the wood decay fungus Perenniporia fraxinea in an urban park in northern Italy

Perenniporia fraxinea is a fungal pathogen causing wood decay in roots and bole of a wide variety of broadleaf tree species. Despite its ecological importance, little is know about the infection biology of this fungus and in particular of its ability to infect trees through the mycelia growth through root contacts. To clarify its spreading mechanisms, a genetic analysis of 20 P. fraxinea isolates obtained from basidiomata collected from closely located Robinia pseudoacacia and Quercus robur trees in the Vernavola Urban Park (Pavia, Italy) and in surrounding areas was performed. Random Amplified Microsatellites (RAMs) fingerprinting was conducted allowing to distinguish 19 different haplotypes. High intrapopulation diversity was confirmed by somatic incompatibility tests (SITs), which were performed by dualculturing isolates in vitro in all possible combinations, resulting in detection of 16 compatibility groups. These results, together with Non-metric MultiDimensional Scaling (NMDS) analysis on genetic data, suggest that spread through root contacts is unlikely for P. fraxinea. In addition, a significant negative correlation between spatial distribution and kinship coefficients was observed in isolates from the Vernavola Urban Park, suggesting a limited dispersal potential of P. fraxinea basidiospores. This report provides a first glimpse of the primary mechanisms of spread of P. fraxinea.