Phytophthora pseudocitrophthora, A New Pathogen of Carnations Causing Root Rot and Basal Stem Necroses in Türkiye

Abstract

A previously unreported root rot and basal stem necrosis disease was observed in carnation (Dianthus caryophyllus) plants grown in greenhouses in Yalova Province, Türkiye, in 2018. A Phytophthora species was consistently isolated from symptomatic root and vascular tissues. Morphological examination revealed a heterothallic species with papillate, usually non‐caducous sporangia (sometimes with double papillae) having ovoid, obpyriform, ellipsoid or nearly spherical shapes, lateral attachment of sporangiophores and spherical chlamydospores in cultures. Mycelial growth on carrot agar occurred between 9.5°C and 31.5°C, with optimum growth at 25°C. Phylogenetic analyses performed using data from three nuclear (ITS, β‐tubulin and heat shock protein 90) and four mitochondrial regions (cytochrome c oxidase subunit 1, cytochrome c oxidase subunit 2, NADH dehydrogenase subunit 1 and ribosomal protein L10) placed isolates in a monophyletic subclade of Phytophthora Clade 2a, matching the recently described species Phytophthora pseudocitrophthora. Pathogenicity trials using soil with inoculated wheat grains showed that isolates induced main root rot and basal stem necroses consistent with field symptoms and significantly reducing root biomass in carnation seedlings within 3 months. All inoculated isolates were reisolated, fulfilling Koch's postulates. This study presents the first report of P. pseudocitrophthora causing disease in carnations and highlights its potential significance in ornamental plant pathology.