Genetic variation of Heterobasidion abietinum in Southern Europe and the Mediterranean Basin

Summary Heterobasidion abietinum causes root and butt rot on Abies species occurring in central Europe and the Mediterranean Basin in a distributionextending from Spain in the west to Turkey and Caucasia in the east. To investigate the genetic diversity within H. abietinum, 95 isolates fromdiﬀerent regions were analysedwith 61 polymorphic molecular markers. The markers showed genetic diﬀerentiation amongst the H. abietinumpopulations. The most diversiﬁed population is that on A. pinsapo in southern Spain, which is isolated from gene ﬂow with other populations.Lower but still signiﬁcant diﬀerences were found amongst other European populations. Isolates from Turkey showed little diversiﬁcationcompared with the south European isolates from east of the Alps. The genetic structure of the H. abietinum populations in relation topostglacial recolonization of Abies is discussed. 1 Introduction Heterobasidion abietinum Niemela¨ & Korhonen, a member of the H. annosum complex, is a pathogen or saprotroph on Abiesspecies occurring in central Europe and in the Mediterranean Basin (Niemela¨ and Korhonen 1998; Woodward et al. 1998;Asiegbu et al. 2005). Its main host species is A. alba Mill. H. abietinum has economic and environmental impacts especially inItaly on A. alba and in Greece on A. cephalonica Loud. and A. borisii-regis Mattf. (Tsopelas and Korhonen 1996; Capretti 1998;Korhonen and Dai 2005). In these countries the damage caused by the fungus is related to stress caused by dry summers(Puddu et al. 2003). In Central Europe and the Pyrenees, H. abietinum is mainly a saprotroph, colonizing mostly stumps andlogs of A. alba and has a lower economic impact than in Italy and Greece (Munda 1994; Łakomy 1996; Korhonen et al. 1998;Puddu et al. 2003; Oliva and Colinas 2010). Other host species of H. abietinum are present in western and eastern regions of the Mediterranean Basin. The westernmosthost is A. pinsapo, a species occurring in a small area of Andalucia, southern Spain (Sa`nchez et al. 2005, 2007). In the east, H.abietinum was recorded on A. cilicica Carr. and A. nordmanniana (Steven) Spach in Turkeyand Russian Caucasia (Korhonen andDai 2005; Dog˘mus¸-Lehtija¨rvi et al. 2006). Recent work investigating genetic variability in H. abietinum populations in the Balkan Peninsula, the Pyrenees and theItalian Peninsula indicated that geographical provenances formed separate clusters (Zamponi et al. 2007). In addition, a highlevel of diﬀerentiation was found between H. abietinum isolates collected from A. pinsapo and those from A. alba in Italy andFrance (Luchi et al. 2008). These previous population studies were performed using the DNA ﬁngerprinting DAMD-PCR (Direct AmpliﬁcationMinisatellite DNA) that includes direct ampliﬁcation of minisatellite-region DNA by the polymerase chain reaction (PCR) usingthe M13 core sequence. This approach had already been applied to studies of genetic variations in H. annosum (Fr.) Bref. sensustricto and H. abietinum (Petta et al. 2001; Zamponi et al. 2007). The utility of RAMS-PCR in studying genetic variability withinthe H. annosum complex (Vainio and Hantula 1999; Dai et al. 2003; DAmico et al. 2007) and other tree pathogens (Vainio et al.1998; Kasanen et al. 2004) was demonstrated previously. The use of these repetitive DNA elements has been applied to studieson population genetics, ecology and taxonomy of many fungi (Wo¨stemeyer and Kreibich 2002). The aim of this study was to investigate the population structure of H. abietinum collected from diﬀerent hosts in severalregions in southern Europe and around the Mediterranean Basin. The work was based on molecular analysis using micro- andminisatellites. In addition, the number of mating factors was identiﬁed from a sample of isolates collected in each locality.