Integrated Characterization of Phytophthora tentaculata Isolated from Diseased Celery in Korea: Morphology, Molecular Identification, Growth and Pathogenicity

In June 2025, celery (Apium graveolens) plants showing wilting and crown rot were collected from commercial fields in Taebaek, Korea. Six oomycete isolates were recovered from symptomatic roots, crowns, and stalks. Based on morphological and cultural characteristics, together with sequence analyses of the internal transcribed spacer (ITS) and cytochrome c oxidase subunit I (cox1) regions, the isolates were identified as Phytophthora tentaculata. Temperature-dependent growth assays on V8 agar (V8A) revealed that all isolates exhibited optimal mycelial growth at 20-25°C, with minimum and maximum growth temperatures of 10°C and 30°C, respectively. Sporangium production varied markedly among culture media and was highest on water agar, followed by 5% V8A, whereas higher V8 concentrations strongly suppressed sporulation. Pathogenicity tests conducted using mycelial plug inoculation resulted in stalk rot, wilting, and plant collapse on celery, consistent with field symptoms. The pathogen was successfully reisolated from symptomatic tissues, whereas no Phytophthora species were recovered from mock-inoculated controls, thereby fulfilling Koch’s postulates. This study represents the first integrated biological and pathological characterization of P. tentaculata associated with celery blight in Korea and provides essential information for accurate diagnosis and improved disease management.