Diversity and Pathogenicity of Phytophthora Species Associated with Declining Alder Trees in Italy and Description of Phytophthora alpina sp. nov

Abstract

Extensive decline and mortality events of alder trees have recently been observed in several riparian ecosystems in Italy. Since there is little information about the aetiology of this disease and given the high ecological relevance of riparian ecosystems, an in-depth study was conducted in three sites spanning from the Mediterranean to Alpine regions. From spring 2019 to spring 2020, 261 samples of bleeding cankers, rhizosphere soil and leaves used as baits along waterways were collected and used for Phytophthora isolation. Based on morphology, colony appearance and DNA sequence data, 10 species belonging to 6 clades were identified. These included P. plurivora (84 isolates), P. pseudocryptogea (50), P. hydropathica (18), P. gonapodyides (14), P. bilorbang (13), P. pseudosyringae (12), P. lacustris (11), P. acerina (7), P. cactorum (1) and one isolate of the hybrid Phytophthora ×serendipita. In addition, two new Phytophthora species, one of which is described here as Phytophthora alpina sp. nov., were isolated. The pathogenicity of P. alpina and other species obtained from samples collected in the green alder stand was assessed on 3-year-old seedlings. All species proved to be pathogenic on green alder causing symptoms congruent with field observations. Results obtained have allowed us to expand knowledge about alder decline aetiology. The diversity of pathogenicity of Phytophthora species associated with symptomatic alder trees suggested that no single agent is responsible for the disease, but that it is the result of multiple infections of different Phytophthora species, variable in assemblages among sites.

The mitogenome of Phytophthora agathidicida: Evidence for a not so recent arrival of the “kauri killing” Phytophthora in New Zealand

“…A recent study [ 79 ] has suggested that biotic (e.g., secondary fungal infections) and abiotic (e.g., extremes in rainfall due to climate change) factors have contributed to Phytophthora -linked decline of European beech ( Fagus sylvatica L.) stands in Lower Austria. Human activity has already severely fragmented kauri forests [ 8 , 14 , 15 ] and this could have exacerbated the impacts of other factors such as climate change (e.g., [ 79 ]) or potentially co-acting pathogens (e.g., [ 80 ]).…”

First Documentation of Life Cycle Completion of the Alien Rust Pathogen Melampsoridium hiratsukanum in the Eastern Alps Proves Its Successful Establishment in This Mountain Range

“…Moreover, starting from 2011, the decline of grey alder in Trentino Alto Adige and South Tyrol was also linked to the occurrence of Phytophthora spp. The presence of these harmful oomycete pathogens on A. incana was recently confirmed in another sector of the eastern Alps, in the Veneto region [31], suggesting this new phytosanitary problem to be greater than expected.…”

Phylogeny and Pathogenicity of Phytophthora Species Associated with Artichoke Crown and Root Rot and Description of Phytophthora marrasii sp. nov.

“…Plant and rhizosphere samples were sealed in plastic bags, labelled, and used for Phytophthora isolations within 48 h. In the laboratory, artichoke samples (rhizosphere soil and necrotic roots) were placed in plastic boxes with 2 L of distilled water. After 24 h at 20 • C, the water surface was cleaned and 5-7 young Quercus suber leaves taken from 5-months-old seedlings were placed on the surface as bait [34]. Boxes were kept at 20 • C under natural daylight for 7 days.…”

“…For the isolates of the new species, another two DNA regions, namely ß-tubulin (Btub) and cytochrome c oxidase subunit I (cox1), were amplified and sequenced using the primer-pairs TUBUF2/TUBUR1 and FM84/FM83 [40,41]. PCR amplification conditions and reaction mixtures were performed, as described by Bregant et al [34].…”

“…Sequences were aligned with ClustalX v. 1.83 [42], using the parameters reported by Bregant et al [34]. Alignments were checked and edited with BioEdit Alignment Editor v. 7.2.5 [43].…”