A pathovar is a bacterial strain or group of strains within a species distinguished by its host range or the specific disease symptoms it causes. The term is primarily used in plant pathology.
Classification and nomenclature
In bacterial taxonomy, subspecies and pathovars allow scientists to differentiate isolates that are genetically similar but differ in biological behaviour. A pathovar designation is appended to the species name to indicate host specificity; for example, Pseudomonas syringae pv. tomato infects tomato plants, while P. syringae pv. lachrymans infects cucurbits. Pathovars are defined based on consistent pathogenic reactions in a particular host and are often determined through inoculation tests. Genetic analyses sometimes reveal minimal differences between pathovars beyond the presence or absence of certain pathogenicity islands or effector genes. The concept is most widely applied to Gram‑negative genera such as Xanthomonas, Pseudomonas and Ralstonia. While useful for practical purposes in plant disease management, the pathovar rank is informal and does not always correspond to clear evolutionary lineages.
Examples and significance
Notable examples include Xanthomonas campestris pv. campestris, which causes black rot in crucifers, and Xanthomonas oryzae pv. oryzae, responsible for bacterial leaf blight of rice. Pseudomonas syringae pv. actinidiae is a pathogen of kiwifruit that has caused significant economic losses through bacterial canker outbreaks. Ralstonia solanacearum has multiple pathovars affecting different solanaceous crops; pv. solanacearum attacks potatoes and tomatoes, while pv. banana targets banana plants. Understanding pathovars aids in accurate diagnosis, quarantine decisions and the development of resistant cultivars. However, as molecular tools evolve, some pathovars may be reclassified as separate species or subspecies when deeper genetic divergence is discovered. Pathovars highlight the diversity of host-pathogen interactions and serve as a practical framework for naming plant-pathogenic bacteria. Related Terms: Pathogen, Bacterial classification, Host specificity, Serovar, Race