Occurrence of soilborne Phytophthora species in declining broadleaf forests in Hungary Ilona Szabó & Ferenc Lakatos & György Sipos Accepted: 29 April 2013 / Published online: 10 May 2013 # KNPV 2013 Abstract Invasive Phytophthora species are responsible for severe tree diseases in many forest ecosystems in Europe. In Hungary, the symptoms were first noted when P. alni infection led to a serious decline and mortality of alder stands in the late 1990s. Between 2001 and 2009, over 300 soilborne Phytophthora isolates were collected from declining broadleaf forests in Hungary, and 10 Phytophthora species identified based on morphological traits and the molecular characteristics of the internally transcribed spacer (ITS) regions of the nuclear ribosomal DNA. The most diverse species spectrum, found in dis- eased alder stands, included P. gonapodyides, P. gregata, P. inundata, P. lacustris, P. megasperma, P. plurivora, one informally designated taxon: P. taxon hungarica, and one unnamed species P. sp.1. P. cactorum and P. plurivora isolates were prevalent in the soil of a de- clining eastern black walnut forest, and three species, P. gonapodyides, P. multivora and P. plurivora were recovered from a declining oak stand. More than one ITS-based genotype was identified for four species, including six genotypes for P. gonapodyides, and two each for P. cactorum, P. plurivora and P. inundata. The high genetic diversity of the P. gonapodyides isolates may indicate that the species is indigenous to the region. In contrast, the frequently recovered, widely distributed P. lacustris with a single ITS ge- notype may represent a recent colonizer. The P. multivora isolates are, to date, the first reported from a European native forest. Keywords Alnus glutinosa . Forest pathology . Juglans nigra . Quercus . ITS-based genotype Introduction The expansion of global trade and human travel has greatly contributed to the increased introduction and spread of invasive pathogens in the past two to three decades (Hulme 2009). In addition to many well adapted indigenous species, the genus Phytophthora (Stramenopila, Oomycota) comprises of some of the most widespread and devastating pathogens for both agricultural and natural ecosystems (Erwin and Ribeiro 1996; Hansen 2008). Several Phytophthora species have been described as invasive and destructive disease agents in forestry. In Europe, P. alni has caused dramatic dieback of Alnus stands in northern and Central Europe (Brasier et al. 1995; Jung and Blaschke 2004). In the UK, P. kernoviae poses a threat to Fagus sylvatica and ornamen- tals, in particular Rhododendron ponticum (Brasier et al. 2005). Both P. cinnamomi and P. ramorum have had deadly impacts on forest ecosystems worldwide, includ- ing in the United States, Europe and Australia (Balci et al. 2007; Brasier and Webber 2010; Cahill et al. 2008). Diseases caused by various Phytophthora species have so far been well documented for several major forest tree species in Europe, including alder (Brasier et al. 1995; Eur J Plant Pathol (2013) 137:159–168 DOI 10.1007/s10658-013-0228-1 I. Szabó (*) : F. Lakatos : G. Sipos Faculty of Forestry, Institute of Silviculture and Forest Protection, University of West Hungary, 9400 Sopron Pf. 132, Hungary e-mail: szaboi@emk.nyme.hu G. Sipos WSL, Swiss Federal Research Institute, CH-8903 Birmensdorf, Zürcherstrasse 111, Switzerland