Phytophthora plurivora and Phytophthora pseudocryptogea isolated from soils supporting declining oaks (Quercus robur L.) in Istanbul, Turkey

Symptoms of decline were first observed on oak trees (Quercus robur) in Emirgan Grove, Istanbul in August 2015. Symptoms included sparse canopies, crown dieback and bleeding cankers on the trunk, usually just above soil level, suggesting Phytophthora infections. Most affected trees lost foliage. No Phytophthora species were isolated from bleeding lesions, although two were obtained using baiting and selective media from soil samples taken around symptomatic trees. Isolates were identified as P. plurivora and P. pseudocryptogea by a combination of morphological characteristics and sequencing of the internal transcribed spacer (ITS) and the cytochrome oxidase I (cox1) gene regions. Inoculations on 2- to 3-year-old Q. robur and Q. suber seedlings demonstrated that both species were pathogenic. Hence, P. plurivora and P. pseudocryptogea may have played roles in the dieback of the oaks, but further work is required to provide definitive conclusions on the cause of the formation of bleeding cankers on oak stems in Istanbul.