Infection and dispersal processes of Pseudomonas syringae pv. coriandricola on coriander

An Australian isolate of Pseudomonas syringae pv. coriandricola (Psc) was used to study aspects of dispersal of the pathogen and infection of coriander. Needle inoculation of Psc in the stem of coriander resulted in up to 94% plant mortality. The total biomass of inoculated plants decreased significantly four weeks after inoculation as compared to the control plants. Systemic infection was rapid and one week after inoculation a bacterial population of about 10⁴ to 10⁸ cfu g^-1 was isolated from different parts of the stems and roots. Surface contamination of coriander seed with Psc prior to planting resulted in low disease incidence (8%). However, spray inoculation of healthy coriander plants with Psc at concentrations equal to or greater than 103 CFU mL^-1 caused disease on the leaves, suggesting infection was common through the stomata. Splash dispersal of Psc was demonstrated, with disease being observed on surrounding coriander seedlings. Psc bacteria were dispersed up to 70 cm from the inoculum source.