Phytophthora, Nothophytophthora and Halophytophthora diversity in rivers, streams and riparian alder ecosystems of Central Europe

Abstract

Waterways are ideal pathways for Phytophthora dispersal and potential introduction to terrestrial ecosystems. While many Phytophthora species from phylogenetic clades 6, 9 and 10 are predominant oomycetes in watercourses due to their adaptation to a lifestyle as saprotrophs and opportunistic pathogens of riparian plants, species from clades 2, 7 and 8 are predominantly soil- or airborne using aquatic habitats as temporal niches for spreading and invading terrestrial sites along the watercourses. In contrast to forest ecosystems, knowledge of Phytophthora diversity in watercourses in Central Europe is limited. Between 2014 and 2019 extensive surveys of streams and rivers were undertaken across Austria, in South Moravia, Czech Republic and Žilina province, Slovakia to unveil the diversity and distribution of Phytophthora and related oomycetes. In addition, in Austria riparian forests of black alder (Alnus glutinosa) and grey alder (A. incana) in lowlands and in the Alps were examined. A variety of Phytophthora species from clades 2, 6, 7, 8, 9 and 10 were isolated, with clade 6 species showing the widest distribution and abundance. Furthermore, interspecific clade 6 hybrids and other oomycetes such as Halophytophthora fluviatilis and undescribed Nothophytophthora spp. were also obtained. In riparian alders, symptoms of Phytophthora infections were associated with species from the P. × alni complex and P. plurivora. Phytophthora plurivora was most common in alder stands whereas P. uniformis was the oomycete species occurring at the highest altitude in alpine riparian areas.

Diversity and distribution of Phytophthora species across different types of riparian vegetation in Italy with the description of Phytophthora heteromorpha sp. nov.

“…Alder decline has been associated for a long time, especially in central Europe, to the attack of the hybrid Phytophthora ×alni [40,41]. However, recent investigations in Austria, Czech Republic, Italy, Portugal and Slovakia, as well as this study, have contributed to better clarifying the aetiology of alder decline, pointing out the key role of P. plurivora in this pathosystem [19,22,24,42]. In the present study, P. plurivora was isolated at very high frequency from bleeding canker, root rot and waterways in 25 sites distributed along a wide altimetric range.…”

Phytophthora Communities Associated with Agathis australis (kauri) in Te Wao Nui o Tiriwa/Waitākere Ranges, New Zealand

“…For example, 13 Phytophthora species were isolated from Alnus glutinosa (L.) Gaertn. (black alder) tissue, rhizosphere, and water samples in Portugal [68], eight species were isolated by soil and nine by water baiting from Quercus suber L. forests in Italy (14 species total) [69], and in a study across Austria, Czech Republic, and Slovakia, 19 Phytophthora taxa were isolated from rivers and streams in Alnus forests [70].…”

Response of Alnus glutinosa to Phytophthora bark infections at ambient and elevated CO2 levels

“…The devastating alder dieback epidemic, caused by the three species from the "Phytophthora alni complex, " was first noticed in the mid 1990s in the UK (Brasier et al, 1999;Gibbs et al, 1999) and is currently widespread along rivers and in alder plantings of most European countries (Jung et al, 2016(Jung et al, , 2018. Phytophthora ×alni (PAA) has been identified as the main causal agent of the disease in most affected regions with temperate climatic conditions but P. ×multiformis (PAM) and P. uniformis (PAU) also cause bark lesions and mortality in the field (Brasier et al, 1999;Nagy et al, 2003;Jung and Blaschke, 2004;Thoirain et al, 2007;Solla et al, 2010;Aguayo et al, 2013;Jung et al, 2013Jung et al, , 2018Štěpánková et al, 2013;Redondo et al, 2015;Corcobado et al, 2023). Only two of the three species, i.e., PAA and PAU, have been recorded in the Czech Republic yet, with PAA strongly prevailing in declining alder stands (88% of 59 declining alder stands studied; Štěpánková et al, 2013).…”

“…In one riparian forest in the Czech Republic, PAA and PAU were isolated from the same declining A. glutinosa tree (Macháčová, unpublished). A range of other Phytophthora species can contribute to the decline of riparian alder stands, most important P. plurivora (PLU) a widespread forest pathogen in Europe with a broad host range that includes A. glutinosa, A. incana and A. viridis (Jung and Blaschke, 2004;Jung and Burgess, 2009;Jung et al, 2013Jung et al, , 2016Jung et al, , 2018Mrázková et al, 2013;Haque et al, 2014;Corcobado et al, 2023;Tkaczyk et al, 2023).…”

“…The Phytophthora genus contains both generalist pathogens like the notorious P. cinnamomi Rands and P. ramorum Werres, De Cock & Man in alni complex" with PAA being more aggressive to A. glutinosa than PAU when infecting black alder (Alnus glutinosa) (Brasier and Kirk, 2001;Santini et al, 2003). Interestingly, PAU was shown to play an increasing role in alder dieback with increasing latitude in Scandinavia and increasing altitude in the Alps which is related to the lower frost tolerance of PAA as compared to PAU (Schumacher et al, 2006;Černý and Strnadová, 2010;Redondo et al, 2015;Corcobado et al, 2023). This is particularly important in the context of ongoing climatic changes and potential spread of the aggressive PAA strains to the currently unfavorable climatic regions.…”