Expansion of Ash Dieback towards the scattered Fraxinus excelsior range of the Italian peninsula

Duccio Migliorini,Alberto Santini,Francesco Pecori,Nicola Luchi,Alessia Lucia Pepori,Emanuele Nigrone

doi:10.1007/s10530-021-02716-z

Duccio Migliorini, Alberto Santini + Show 4 more

Open Access

https://doi.org/10.1007/s10530-021-02716-z

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Abstract

Hymenoscyphus fraxineus, causal agent of Ash Dieback, has posed a threat to Fraxinus excelsior (common ash) in Europe since the 1990s. In south-western Europe, optimal climatic conditions for H. fraxineus become scattered and host density decreases, reducing disease spread rates. To date, the Ash Dieback agent has not been reported from southern and most of central Italy, where native F. excelsior is present as small fragmented populations. This study examines the expansion of Ash Dieback into central Italy, and it considers the consequences of further local spread with regards to the loss of F. excelsior genetic resource. Symptomatic F. excelsior were sampled from sixteen sites in northern and central Italy during 2020. Specimens were analyzed with a culturomics and a quantitative PCR approach. A bibliographic search of F. excelsior floristic reports was conducted for the creation of a detailed range map. The combined use of both techniques confirmed the presence of H. fraxineus in all the sites of central Italy where host plants were symptomatic. These new records represent the southern limit of the current known distribution of this pathogen in Italy, and together with Montenegro, in Europe. The characterization of the F. excelsior scattered range suggests that further spread of Ash Dieback across southern Italy is a realistic scenario. This presents a threat not just to the southern European proveniences of F. excelsior, but to the species as a whole, should Ash Dieback lead to the loss of warm climate adapted genetic material, which may become increasingly valuable under climate change.

Highlights

Hymenoscyphus fraxineus, causal agent of Ash Dieback, has posed a threat to Fraxinus excelsior in Europe since the 1990s
The southern and western limits of H. fraxineus in Europe are currently represented by Montenegro in the Balkans (Milenkovicet al. 2017), Central Italy (Ghelardini et al 2017) and Central France (Grosdidier et al 2018a)
The aim of this study is to describe the present spread of the Ash Dieback epidemic in central Italy, and to draw attention to its possible threat for F. excelsior in the stands where the pathogen is not yet present

Summary

Introduction

Hymenoscyphus fraxineus, causal agent of Ash Dieback, has posed a threat to Fraxinus excelsior (common ash) in Europe since the 1990s. The suitable environmental conditions for disease development are represented by abundant summer precipitation, high soil moisture and low air temperature (Dal Maso and Montecchio 2014) These conditions are common in central and northern European countries, where the pathogen spread fast from the early years of its establishment in the continent (Pautasso et al 2013). In southern Italy, sites suitable for the establishment of the fungus are present, especially along the Apennines chain (Dal Maso and Montecchio 2014; Ghelardini et al 2017) Human mediated or natural, localized introductions of H. fraxineus cannot be excluded

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