Phytophthora species causing root and crown rot of apple trees in Türkiye

Phytophthora root and crown rot is one of the most destructive diseases of apple trees. The presence of Phytophthora species in apple trees was investigated in commercial apple orchards in Isparta, Karaman and Niğde provinces, the main apple-growing region of Türkiye. Root-crown and soil samples were collected from symptomatic trees. In addition, young diseased apple trees were taken from other several provinces of Türkiye, including Aksaray, Ankara, Antalya, Kayseri, Konya and Yozgat. Phytophthora species were isolated from canker lesions on main roots or crowns as well as from the rhizosphere soil of apple trees showing characteristic symptoms of Phytophthora root and crown rot. The isolates obtained were identified as P. cactorum, P. cryptogea, P. plurivora, P. rosacearum and P. taxon walnut using morphological features and confirmed by sequencing the internal transcribed spacer (ITS), beta-tubulin (tub2) and cytochrome oxidase I (cox1) gene regions of the isolates. Phytophthora cactorum, obtained from all provinces was the most frequently isolated species. Other species were less common: P. plurivora isolates were obtained only from Isparta and P. cryptogea, P. rosacearum and P. taxon walnut isolates only from Karaman. Representative isolates of all species were pathogenic on excised twigs and roots of one-year-old MM.106 apple rootstock, with P. cactorum being the most aggressive. This study is the first report of P. cryptogea, P. plurivora and P. rosacearum causing root and crown rot on apple trees in Türkiye, and indicating that P. taxon walnut is a new pathogen of apple.