Perenniporia fraxinea population: a case of study in an unrban park at Pavia (Italy)

Perenniporia fraxinea is either a parasite or a saprotrophic fungus growing on a wide variety of hardwood trees species. Fruiting bodies are perennial, pileate, large, single or imbricate, woody. The fungus is reported in forests, gardens and parks, but also on street trees where it usually causes white rot on the lowest parts of the stem, rarely on emerging roots (1). Therefore, this species can affect the stability of trees, with possible consequences for people and properties. The populations of pathogens like P. fraxinea are often studied by using molecular techniques associated with morphological studies such as somatic incompatibility tests (2). Despite its wide distribution, areas where P. fraxinea fruiting bodies are abundant look uncommon, so that intra- and interpopulation comparison can be hard to perform (3). In Pavia municipality (Lombardy, Italy) this species is abundant and is likely to be one of the most widespread tree pathogens in urban areas. The present investigation aimed at better understanding P. fraxinea populations. In particular, genetic variation among P. fraxinea isolates collected from fruiting bodies found on closely located trees was investigated, coupling molecular analysis with somatic incompatibility tests. Fruiting bodies were mostly collected in Pavia municipality, namely Parco della Vernavola; a few samples were also collected from surrounding urban sites and from other municipalities as outsiders (xx). Analyses through RAMS (random amplified microsatellites) pointed out a high genetic diversity among isolates even if they were collected only few meters far from each other. This finding may suggest the spread through root contacts is unlikely for this fungus. Somatic incompatibility tests confirmed the diversity, but failed to distinguish all genotypes identified through RAMs.. A significant correlation between genetic diversity and spatial distribution of isolates collected in Parco della Vernavola was observed. This is one of the first reports on the populations of P. fraxinea.