Diversity of Phytophthora Species Involved in New Diseases of Mountain Vegetation in Europe with the Description of Phytophthora pseudogregata sp. nov.

Abstract

New and emerging Phytophthora-related diseases in small trees, shrubs and herbaceous plants typical of subalpine vegetation have recently been observed in Italy and Slovenia. Diseased plants showed a complex symptomatology including foliar necrosis, fruit rot, shoot blight and branch bleeding cankers. Since little information is available about the aetiology of these aerial Phytophthora diseases, from 2019 to 2022, field surveys were conducted in 54 sites to define the occurrence, distribution and impact of the Phytophthora species on mountain vegetation. A total of 360 Phytophthora isolates were obtained from 397 samples collected from 33 herbaceous and woody host species. Based on phylogenetic analysis and morphometric data, 17 Phytophthora species were identified: P. pseudosyringae (201 isolates), P. plurivora (54), P. gonapodyides (21), P. ilicis (20), P. alpina (17), P. acerina (11), P. cactorum (7), P. pseudocryptogea (6), P. cambivora (5), P. idaei (4), P. psychrophila (3), P. bilorbang (2), P. chlamydospora (2), P. hedraiandra (1), P. kelmanii (1), P. rosacearum (1) and P. syringae (1). In addition, three isolates of a new putative Phytophthora species obtained from Alnus viridis, Juniperus communis and Rhododendron ferrugineum are described here as Phytophthora pseudogregata sp. nov. Overall, the results highlighted an unexpectedly high diversity of Phytophthora species in mountain areas, with many species able to cause aerial infections due to the production of caducous sporangia.

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

“…The aerial lifestyle of P. pseudosyringae is related to the production of caducous sporangia, able to spread as infective propagules on epigeal plant organs, producing leaf necrosis and bleeding cankers [17]. Its importance as an invasive species is growing very rapidly; recently it has been reported associated with severe diseases on 25 hosts in the Italian and Slovenian mountains [17]. Pathogenicity tests on grey alder confirmed the high virulence of this species.…”

“…PCR was performed in 50 ml reaction mixtures using the GoTaq Hot Start Green Master Mix (Promega) and a SimpliAmp Thermal Cycler (Thermo Fisher Scientific Inc.). Amplification conditions for the three regions were conducted as described in Bregant et al [17].…”

“…7). Notes -Isolates of P. heteromorpha share some of the common characters of the species belonging to subclade 6b [17,39]. However, P. heteromorpha can easily be distinguished from the closest species based on a combination of genetic and morphological differences (Tables 5 and S1).…”

“…Despite the extreme adaptability to rapid environmental modifications, riparian systems appear to be more vulnerable than other forest formations to diseases. In the last decades, severe decline events have severally impacted many riparian ecosystems worldwide [14][15][16][17]. In particular, an increasing number of outbreaks caused by Phytophthora species have been reported on alders [18,19].…”

“…Given the alarming decline and mortality affecting riparian species in Italy [17,19,24,25] and the still limited information on the pathogens involved, a study was conducted in 46 riparian formations distributed from the Mediterranean to the alpine climate to isolate and characterize the main pathogens associated.…”