An overview on Phytophthora spp. associated with Mediterranean oak decline in Sardinia

Abstract: Since the beginning of the 20th century, Mediterranean oak forests have been threatened by several factors including human intervention, climate change and attacks of pathogens and pests. Several studies have demonstrated the primary role of the oomycete Phytophthora cinnamomi in the widespread decline of Mediterranean oaks in Portugal, Spain, southern France and Italy, although other Phytophthora species have been also associated with this phenomenon. Since almost 7 years, independent surveys have been undertaken to investigate the diversity and distribution of Phytophthora species associated with declining oak trees in Sardinia (Italy). Root and soil samples were collected from symptomatic oak trees located in natural and managed forests, new plantations and afforestated areas, parks, gardens and forest nurseries. Different methods of isolation were used, including soil baiting with leaves as well as direct isolation from infected root and bark tissues on selective medium. All the obtained species were identified based on colony morphologies and ITS sequences analysis. A total of 13 Phytophthora spp. were detected from Q. ilex and Q. suber declining trees. This is the first long-term study looking at the diversity of Phytophthora spp. in oak ecosystems in Italy.