Impact of Phytopythium vexans on Plant Health: Hosts, Symptoms, Detection, and Management

Abstract Phytopythium vexans is an emerging phytopathogenic oomycete reported to be causing diseases in plants from multiple genera and families. It is a soil and water-inhabiting oomycete with sexual and asexual life cycles present in the environment. Sexual stages produce oospores whereas asexual stages produce zoospores. This pathogen has been reported to be infecting crops in Africa, Asia, Europe, North America, Oceania, and South America. Mainly root and crown regions of numerous perennial woody plants, herbaceous and weedy annual cereal crops, forest plants, ornamental plants, and fruit trees are reported to be infected. Certain names for the symptoms of pathogen infections associated with the host have been used such as replant disease, decline, and sadness syndrome. Young plants that are vegetatively propagated if infected die off in severe cases whereas in the case of older plants, the roots and crown regions are mainly affected by this pathogen. Infections typically display symptoms of brown necrosis in the roots and stem, with a soft, watery rotting mass inside in case of heavily infected samples. Upon gentle pulling, the outer bark sloughs off, revealing the extent of the damage. It also causes damping-off of seedlings. The pathogen moves within water and hence has the potential to induce chains of disease outbreaks in nurseries and greenhouses. A saturated soil for longer periods of time favors tissue colonization and disease progress since the water-loving infectious zoospores of this pathogen can swim to distances that directly favor the pathogen. Higher nitrogen content in the soil, reduced availability of oxygen in the soil, and decreased ability of the plant to grow at lower temperatures created by water stagnation are additional epidemiological factors that favor the disease development. An integrated approach, which includes early detection of the pathogen using culture-based assay/molecular approaches, use of preventive and curative fungicides/biofungicides, and cultural practices, is recommended for the management of Phytopythium . Use of cover crops, soil solarization, crop rotation with non-hosts, and biofumigation to suppress or kill the pathogen are recommended. Testing of irrigation water for the presence of pathogens and treatment using a combination of different measures such as filtration plus UV, ozone, and heat is also recommended. Information © The Authors 2023