02329nas a2200205 4500008004100000022001400041245010500055210006900160260002900229300001400258490000700272520168900279100002001968700001501988700001802003700001702021700001802038700001202056856005502068 2011 eng d a1439-032900aPhytophthora root and collar rot of mature Fraxinus excelsior in forest stands in Poland and Denmark0 aPhytophthora root and collar rot of mature Fraxinus excelsior in bBlackwell Publishing Ltd a510–5190 v413 a

In recent years, Common ash (Fraxinus excelsior) throughout Europe has been severely impacted by a leaf and twig dieback caused by the hyphomycete Chalara fraxinea. The reasons for its current devastating outbreak, however, still remain unclear. Here, we report the presence of four Phytophthora taxa in declining ash stands in Poland and Denmark. Phytophthora cactorum, Phytophthora plurivora, Phytophthora taxon salixsoil and Phytophthora gonapodyides were isolated from rhizosphere soil samples and necrotic bark lesions on stems and roots of mature declining ash trees in four stands. The first three species proved to be aggressive to abscised roots, twigs and leaves of F. excelsior in inoculation experiments. Soil infestation tests also confirmed their pathogenicity towards fine and feeder roots of ash seedlings. Our results provide first evidence for an involvement of Phytophthora species as a contributing factor in current decline phenomena of F. excelsior across Europe. Specifically, they may act as a predisposing factor for trees subsequently infected by C. fraxinea. Phytophthora species from ash stands also proved to be aggressive towards a wide range of tree and shrub species commonly associated with F. excelsior in mixed stands. Although damage varied considerably depending on the Phytophthora species/isolate-host plant combination, these results show that many woody species may be a potential source for survival and inoculum build-up of soilborne Phytophthora spp. in ash stands and forest ecosystems in general.

1 aOrlikowski, L B1 aPtaszek, M1 aRodziewicz, A1 aNechwatal, J1 aThinggaard, K1 aJung, T uhttp://dx.doi.org/10.1111/j.1439-0329.2011.00714.x