Exploring the Diversity of Phytophthora spp. and the role Phytophthora multivora in Cork and Holm Oak coastal forests in Italy

Abstract

Phytophthora cinnamomi and Phytophthora multivora are considered important forest pathogens in different areas of the world. However, while P. cinnamomi presence and impact are widely reported, 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 classical (baiting) and metabarcoding (HTS). 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 and barcoding. 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 soilborne community did not differ among tree hosts. Phytophthora cinnamomi was the most common species in the investigated site. The aggressiveness of P. multivora to holm and cork oak was evaluated on 3 months old seedlings using soil infestation and keeping 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. cinnamomic. Holm oak resulted the most sensitive host to both 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. However, in consideration of its sensible activity as a fine root feeder and adaptation to dry environments, its role in holm and cork oak decline could become relevant in the medium-term specifically in association with climate changes.