First report of Phytophthora taxon walnut in Lombardy, North Italy

The park Boscoincittà, Milan, North Italy (136 m a.s.l., 45°29′06″ N, 9°5′32″ E), has an area of 110 ha and includes tree stands, wood clearings, trails, and watercourses. Recently, common walnut (Jugland regia) trees in the park have begun to suffer from a progressive dieback that has caused roughly 90% mortality. This is the first report of Phytophthora taxon walnut from Italy. Members of the Phytophthora genus grouping with the Phytophthora taxon walnut in clade 6 are mainly reported as saprophytes or pathogens from riparian ecosystems and forests. Since the oomycete proved in our growth trial to be distinctly thermophilic, we hypothesize that its spread is being favored by the rising temperatures observed during the last decades in the area.