Of the published methods to distinguish Pseudomonas syringae pv. syringae and Pseudomonas syringae pv. pisi, inoculation of susceptible cultivars was the most reliable. Results were confirmed by inoculation of lemon fruit.
A much more rapid and convenient serological method was developed to distinguish the two pathovars. Antisera against glutaraldehyde-fixed cells had a high level of specificity in Ouchterlony gel double-diffusion tests and, after cross-absorption with heterologous antigens, in indirect ELISA. Antiserum to P. syringae pv. pisi has considerable potential to detect pea seed infected with this pathogen.