Etiology and Pathogenicity of Phytophthora cryptogea Causing Crown Rot on Gerbera in Greenhouse Production

Abstract

Crown rot symptoms observed in greenhouse-grown gerbera (Gerbera jamesonii L.) were investigated to determine the etiology and pathogenicity of Phytophthora cryptogea. Affected plants exhibited crown discoloration, basal stem necrosis, chlorosis, wilting, and rapid plant collapse under high humidity and excessive irrigation conditions typical of protected cultivation systems. Isolation from infected crown tissues yielded fast-growing oomycete cultures on selective media, producing coenocytic hyphae characteristic of Phytophthora species. Morphological identification was supported by the production of ovoid to pyriform sporangia and occasional zoospore release under flooded conditions. Pathogenicity assays conducted on healthy gerbera plants under controlled greenhouse conditions successfully reproduced crown rot symptoms, confirming the causal role of P. cryptogea and fulfilling Koch’s postulates. Molecular characterization using ITS rDNA and cytochrome oxidase subunit I (cox1) gene sequencing confirmed species identity, with isolates clustering within a well-supported P. cryptogea clade and showing high similarity to global reference isolates. Limited genetic variation among isolates suggested a relatively uniform pathogen population in the surveyed production systems. Disease severity was strongly associated with poor drainage, over-irrigation, and warm humid greenhouse environments, which favored zoospore production and infection. The study highlights the high pathogenic potential of P. cryptogea in ornamental gerbera cultivation and underscores its significance as a major constraint in greenhouse production systems. Integrated disease management strategies, including improved irrigation scheduling, sanitation, substrate disinfection, and the use of resistant or tolerant cultivars, are recommended to reduce disease incidence and improve crop sustainability in protected horticultural systems.