Most soilborne Phytophthora species are invasive plant pathogens and nursery plants for transplanting are considered a primary pathway for the introduction of exotic Phytophthora species into plant diversity conservation areas and sites. As a preliminary step toward investigating this subject, we compared the diversity of Phytophthora in the protected natural area Complesso Speleologico Villasmundo S. Alfio Nature Reserve (NR) (Melilli, Siracusa) and the botanical garden (BG) of the University of Catania (Catania), in eastern Sicily (southern Italy). Sampling was carried out during the spring of 2019. Overall 29 rhizosphere soil samples were collected, 17 from different types of vegetation in NR and 12 from different plant species in BG. Phytophthora species were recovered from soil samples by leaf baiting and subsequent isolation on a selective medium. Isolates were identified by combining macro- and micro-morphological features with phylogenetic inferences from ITS-rDNA sequence analysis.

Overall 82 Phytophthora isolates, 30 from NR and 52 from BG, were characterized. Five Phytophthora species, P. pseudocryptogea, P. cryptogea, P. bilorbang, P. plurivora and P. gonapodyides, were recovered in the nature reserve, while only three species, P. nicotianae, P. multivora and P. parvispora, were found in the botanical garden. It can be concluded that the most aggressive and polyphagous species, P. nicotianae, P. multivora and P. parvispora, were recovered in the botanical garden, while Phytophthora species characterized by the ability to either survive in aquatic environments or complete their lifecycle as saprobes, such as P. bilorbang and P. gonapodyides, were only present in the nature reserve. It is noteworthy that the organic carbon content was higher in soil of the nature reserve while the nitrate content was higher in the soil of botanical garden. The role of soil properties in conditioning the ecology of diverse Phytophthora species deserves to be further investigated.