= Bacterial host range
<Bacterial host range> describes the hosts in which a specified <bacterial strain> can establish a defined biological interaction, such as sustained colonization or disease. The endpoint must be stated: detecting the bacterium, observing growth and measuring host damage are different observations. In plant-pathogen classification, a <pathovar> summarizes disease-response characteristics in one or more hosts.<International Code of Nomenclature of Prokaryotes. Prokaryotic Code (2022 Revision) by Aharon Oren and others>[Appendix10B, Pathovar/Pathotype row]{ref}
<Pseudomonas syringae pv. tomato DC3000> provides a concrete example of a label that does not enumerate the complete range. Its genome paper identifies both tomato and <Arabidopsis thaliana> as susceptible hosts.<The complete genome sequence of the Arabidopsis and tomato pathogen Pseudomonas syringae pv. tomato DC3000 by C. Robin Buell and others>[Abstract, disease on tomato and Arabidopsis]{ref} The pathovar word tomato therefore cannot be interpreted as an exclusive host list.
For a hypothetical three-host panel, strain X gives the chosen response in hosts A and B, while strain Y does so in hosts A and C. Both have two positive hosts, yet their tested ranges differ; counting positives discards which hosts they were. An untested host D remains unclassified by this panel. Even a negative observation is conditional on the readout and setting.
A 2011 experiment illustrates that context: prior colonization by some <Sphingomonas> strains reduced DC3000 growth and disease symptoms in <Arabidopsis thaliana>.<Protection of Arabidopsis thaliana against leaf-pathogenic Pseudomonas syringae by Sphingomonas strains in a controlled model system by Gerd Innerebner and others>[Abstract and Figure2, colonist comparison]{ref} A changed disease outcome in one host need not imply a change in host identity or a newly established species-wide host boundary.
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