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studied and described in details (Diminić 1997) it was unclear which abiotic and biotic factors are detrimental for disease outbreak. Results of Diminić et al. (2003; 2012) revealed the predisposition of Austrian pine to Sphaeropsis tip blight infection depending on bedrock, soil type and water availability. Draught was also highlighted as a crucial stress factor in north Dalmatia, Croatia, which predispose pines for different pathogen attack (Pernek et al. 2012). Afterwards, Austrian pine plantations with higher ratio of ectomycorrhizal (ECM) fungal species in the total number of recorded species were confirmed as more resistant to S. sapinea infection (Zgrablić et al. 2015). Although fungi play a crucial role in forest ecosystem stability acting as saprotrophs, symbionts or parasites (Zgrablić et al. 2014), they still represent a large group of organisms that lack fundamental knowledge of their diversity on global scale (Kuyper 1994; Tkalčec et al. 2008). Fungal diversity on Earth is estimated to 1.5 up to 7 million species, with many species still waiting to be described (Blackwell 2011; Kuyper & Giller 2011). This confirms that biodiversity as a global concept of variety of life, is crucial for sustainable functioning and survival of ecosystems on Earth (Perini & Laganà 2004). According to various authors, a healthy forest ecosystem contains 40-60% of mycorrhizal species and fruit bodies in the total count of present species and their fruit bodies (both mycorrhizal and saprobic) (Arnolds 1991; Fellner 1989, 1993; Fellner & Peškova 1995; Egli 2011). It is well known that mycorrhizal plants are more resistant to biotic and abiotic stress, transplantation stress, soil pathogens, high temperatures, salinity and extreme pH soil conditions (Kendrick 2000; Palermo et al. 2003; Perotto et al. 2013). Subsequently, many studies were conducted to describe the performance of inoculated seedlings and mycorrhizal communities of forests damaged by air pollution. Resistance of Norway spruce seedlings roots with different mycorrhizal inoculums were tested to prevent the attack of honey fungus (Armillaria (Fr.) Staude) in the Czech Republic. Treated seedlings showed significantly higher dimensions than the control sample even in the areas of honey fungus high infection rate (Holuša et al. 2009). Different authors described the decline of mycorrhizal fungal communities caused by air pollutants (Termorshuizen & Schaffers 1987, 1989; Arnolds 1991; Fellner 1993; Fellner & Pešková 1995; Matočec et al. 2000; Pešková 2005, 2007; Kraigher et al. 2007). Deciduous and coniferous forests were studied in Czech Republic where stands were grouped in three classes according to their health status (latent, acute and lethal). The results clearly indicated the connection of trees crown transparency and the number of mycorrhizal species and their fruit bodies. Furthermore, it was determined that percentage of active and non-active mycorrhiza on root tips strongly depends on host plant health condition, same as on health condition of entire forest (Fellner 1993; Fellner and Peškova 1995). Studies of Quercus ilex L. forests from Italy, where selected trees were grouped in three different health classes, showed only 25% of common fungal species between the classes. This indicated that altered health conditions influence the ECM community, meaning that a healthy tree can choose its mycorrhizal partner less demanding in terms of nutrients, while the infected tree loses this possibility (Druebert et al. 2009; Montecchio et al. 2009). Mycorrhizal communities of sweet chestnut (Castanea sativa Mill.) forests in Italy affected by ink disease (Phytophthora cambivora (Petri) Buism.) were studied, where selected trees were classified according to ink disease symptoms in three classes. Oppositely than expected, number of mycorrhizal morphotypes on chestnut roots was not significantly different between the classes. However, cluster analyses revealed that with increasing symptoms of ink disease, the ECM community was more similar, whereas asymptomatic trees differed significantly from symptomatic classes and inside the group (Scattolin et al., 2012). Despite to all above mentioned results, there is a substantial gap of knowledge on interaction between fungal diversity as a potential indicator of Austrian pine plantations resistance towards disease outbreak and S. sapinea infection rate. S. sapinea is a very specific pathogen that causes the damage or a dieback of Austrian pine in natural habitats or plantations all over the world (Swart & Wingfield 1991; Diminić 1997). Its principal characteristic is the possibility to attack all parts of the tree that had suffered abiotic stress, mainly draught (Diminić et al. 2012). The pathogen can live as an endophyte in the healthy pine needles without causing any damage for years, but abiotic stress can act as a trigger to activate its parasitic stage of life (Stanosz et al. 2001; Deriu 2010). Among Austrian pine plantations in Istria, we observed differences in species composition and richness. Considering the principles of integrated forest protection as more sustainable and environmentally less harmful method in relation to conventional use of pesticides in forest protection (Feldmann et al. 2003), in this research, for the first time, we studied macrofungal diversity as a potential indicator of tree health status and S. sapinea infection rate, respectively. From the present knowledge and observations, we draw our hypotheses that plantations with higher diversity of fungal species (species richness), are more resistant to S. sapinea infection outbreak. More precisely, we tested the total and ECM species richness, and Shannon diversity index for the total count of species and for ECM species only, in relation towards an average number of S. sapinea pycnidia on needles and an average crown transparency of Austrian pines. Materials and Methods Materijali i metode rada Fungal samples were collected in Istria region (Croatia), Forest administration Buzet, at nine permanent research |