Phytophthora Diversity in a Sentinel Arboretum and in a Nature Reserve Area

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 sites. As a preliminary contribution to the study of Phytophthora populations in plant conservation sites, we compared the diversity of Phytophthora in the protected natural area Complesso Speleologico Villasmundo S. Alfio Nature Reserve (NR) (Siracusa) and the botanical garden (BG) of the University of Catania, eastern Sicily (Italy). Samplings were carried out in spring 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 isolation on a selective medium. Isolates were identified by combining 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 from NR, while only three species, P. nicotianae, P. multivora and P. parvispora, were found in BG. Factors contributing to shape Phytophthora populations of rhizosphere soil in these two vegetational contexts are discussed.