Exploring the diversity of Phytophthora spp . and the role of Phytophthora multivora in cork and holm oak coastal forests in Italy

Phytophthora cinnamomi and Phytophthora multivora are considered important forest pathogens globally. The presence of P. cinnamomi is widely reported, but little is known about the presence of Phytophthora multivora in the Mediterranean evergreen oak forests and its possible role in their decline syndrome. The present study was conducted to identify the presence of P. cinnamomi , P. multivora , and other Phytophthora species in the Castelporziano Presidential Estate in Italy using both soil-baiting and metabarcoding approaches. A total of 52 rhizosphere soil samples were collected from declining oak stands, from which 254 isolates of oomycetes taxa were obtained among which Phytophthora cinnamomi , P. multivora , P. plurivora , P. gonapodyides , and P. bilorbang were identified based on morphological traits. The results of HTS analysis revealed the presence in the rhizosphere of 20 different Phytophthora spp . including all the taxa obtained through baiting. Interestingly, the Phytophthora community did not differ among tree hosts. Phytophthora cinnamomi was the most common species in the investigated site. The pathogenicity of P. multivora to holm and cork oaks was evaluated on 3-month-old seedlings using P. cinnamomi as the positive control. Soil inoculation test demonstrated the aggressiveness of P. multivora on both holm oak and cork oak. Phytophthora multivora resulted by far less aggressive than P. cinnamomi . Among the host tree species, holm oak had a higher susceptibility to both tested pathogens. While P. multivora seems to play a relevant role in the decline of forest and urban ecosystems in Australia, its role in evergreen oak decline seems to be limited at the moment. Considering the nature of P. multivora as a fine root feeder and adaptation to dry environments, its role in holm and cork oaks decline could become more relevant in the medium term specifically in association with climate change.