Pseudomonas syringae pv. porri (Pspo) is the causal organism of bacterial blight of leek. This pathogen can be seed-borne and therefore the testing of seeds of leek is common. Seeds of leek can be saprophyte-rich and this might disguise the presence of Pspo. Detection of this bacterium is performed by dilution plating on highly selective media such as KBBC and PSM (Pseudomonas Syringae Medium). Putative Pspo colonies are then transferred to KB. Thereafter the identity of the suspected colonies is determined by immunofluorescence microscopy. Finally, the identity is determined by a Pspo-specific PCR or a pathogenicity assay using seedlings of leek. On PSM the colonies of Pspo are 2-4 mm in diameter, circular with smooth edge, translucent, creamy-yellow to transparant white. Note that the color of Pspo colonies is rather variable since the accumulation of bromothymol blue per colony is strongly dependent on the total number of colonies per plate. For detailed information about Duchefa’s Phytopathological media have a look at our specialized brochure about this topic. Brochure can be found at the “Brochure section” at the home page of this website.