Benedetto Teodoro Linaldeddu

Riparian formations encompass a diverse suite of transitional zones between terrestrial and aquatic ecosystems. During the last decades, these formations have been impacted by several emerging diseases. The first outbreaks were detected on alder formations, but have progressively also been observed on other plant species such as Betula pubescens , Nerium oleander , Populus alba , Salix alpina , Salix purpurea and Tamarix gallica . Declining plants showed a plethora of symptoms (leaf spot, shoot blight, bleeding cankers and root rot) indicative of Phytophthora infections. Since there is little information about the aetiology of these pathosystems, from November 2019 to March 2023, an in-depth study was conducted in 46 riparian ecosystems spanning from the Mediterranean to Alpine regions. Overall, 744 symptomatic samples (stem bleeding cankers and root with rhizosphere) from 27 host species were collected for Phytophthora isolation. Based on morphology and DNA sequence data, 20 known Phytophthora species belonging to seven phylogenetic clades have been identified: P. plurivora (202 isolates), P. gonapodyides (156), P. pseudosyringae (84), P. lacustris (57), P. acerina (31), P. idaei (30), P. alpina (20), P. pseudocryptogea (19), P. cambivora (13), P. pseudotsugae (13), P. cactorum (9), P. honggalleglyana (6), P. pseudogregata (6), P. debattistii (4), P. multivora (4), P. cinnamomi (3), P. bilorbang (2) P. crassamura (2), P. ilicis (2) and P. inundata (2). In addition, 26 isolates of a new putative species obtained from Alnus incana and Pinus sylvestris are described here as Phytophthora heteromorpha sp. nov. The new species proved to be pathogenic on grey alder causing symptoms congruent with field observations. This study represents the most comprehensive investigation on the Phytophthora species associated with declining riparian vegetation in Italy and highlights that the polyphagous pathogen P. plurivora represents a growing threat to Mediterranean, temperate and alpine ecosystems.

Extensive collar rot, sunken and bleeding cankers, shoot blight, and fruit rot symptoms on olive trees have recently been observed in several orchards in Italy. Since there is little information about the etiology of these diseases and given the high economic relevance of this iconic crop, a study was conducted from autumn 2017 to summer 2022, in four Italian regions, to define the occurrence, distribution and impact of the main pathogens involved. A total of 1064 symptomatic olive samples were collected and processed. Based on colony appearance, micromorphological analysis and DNA sequence data, thirty-eight species, including eighteen Botryosphaeriaceae species belonging to five genera and fifteen Phytophthora species, were isolated and identified, thirteen of which, Diplodia africana, D. fraxini, D. subglobosa, Dothiorella omnivora, Do. sarmentorum, Do. sempervirentis, Sardiniella urbana (Botryosphaeriaceae), Phytophthora cactorum, P. cinnamomi, P. citricola, P. crassamura, P. niederhauserii and P. pseudocryptogea, are reported here for the first time in olive trees. Pathogenicity tests performed on unripe drupes and on potted olive seedlings completed Koch postulates and highlighted that several species of Botryosphaeriaceae and Phytophthora represent a growing threat to olive trees.