PTSA (Peptone Tyrosine Sodium chloride Agar) is a semi-selectivemedium for the detection of Xanthomonas axonopodis pv. phaseoli in bean seed. The medium is not very selective in com-parison with mXCP1, but especially colonies from the var. fus-cans are easily recognized on this medium because of their excessive production of visible brown pigment. The non-fuscansisolates of Xap grow well on PTSA medium but their recognition is much more difficult due to the lack of pigment production. For relatively clean seed lots, PTSA medium is useful, but for saprophyte-rich samples mXCP1 is much more suitable. Xap is detected by dilution plating of bacterial extract from seeds on PTSA. Then suspected colonies from PTSA should be transferred to YDC. Finally, the identity of suspected isolates isconfirmed by a pathogenicity test or PCR.Colonies of Xap var. fuscans are distinguished by brown pigmentation. For detailed information about DuchefaÂ’s Phytopathological media have a look at our specialized brochure about this topic. Brochure can be found at the Â“Brochure sectionÂ” at the home page of this website.