Distribution of Phytophthora oleae in Southern Italy.

Phytophthora oleae, a recently described new homothallic species in clade 2 with an optimum temperature of about 20 °C and persistent, semi-papillate sporangia, causes occasional outbreaks of rot on mature olive drupes. Its geographical distribution has been investigated in olive orchards in Calabria using carob (Ceratonia siliqua) leaf baiting and selective isolation medium for Phytophthora. Isolates were identified by sequencing the ITS1-5.8S-ITS2 region of rDNA and cox1 gene. The species was recovered from rhizosphere soil and fine roots of olive trees in a relatively large area along the Tyrrhenian coast of Calabria with no apparent association with root rot and decline symptoms on the tree canopy. Reports of P. oleae in undisturbed naturalized riparian ecosystems in Sicily (where olive is an essential and characteristic component of phytocenosysis) as well as in protected natural area in Spain (where P. oleae was associated with root rot of wild olive) raise the questions whether its natural host range is restricted to olive or it is a polyphagous species like its close relatives in clade 2, and whether it is a recently introduced, invasive pathogen or a naturalized, occasional, weak pathogen in olive stands.