Biological and Molecular Evidence that Pseudomonas syringae Pathovars coronafaciens, striafaciens and garcae are Likely the Same Pathovar

Abstract Using a combination of physiological tests, molecular analysis and assays, we investigated the taxonomic relationship among the oat pathogens Pseudomonas syringae pv. coronafaciens (halo blight) and P. syringae pv. striafaciens (bacterial stripe) and the coffee pathogen P. syringae pv. garcae (bacterial blight). Pseudomonas syringae pvs coronafaciens and garcae produce tabtoxin while P. syringae pv. striafaciens is tabtoxin‐deficient. Physiological tests did not show significant differences among these three pathovars (pvs). Analysis using DNA ‘fingerprint’ and Southern blot analysis revealed that P. syringae pvs coronafaciens, striafaciens and garcae are molecularly very similar except that pv. striafaciens appears to have lost part or all of the tabtoxin biosynthetic region. Significantly, P. syringae pv. garcae was pathogenic on oat leaves and indistinguishable from P. syringae pv. coronafaciens in our laboratory assays. Introduction of tabtoxin biosynthetic region contained on the cosmid pRTBL823 resulted in tabtoxin production by P. syringae pv. striafaciens and the production of lesions on oat leaves that were indistinguishable for those caused by P. syringae pv. coronafaciens. Taken together, our data strongly suggests that the P. syringae pvs coronafaciens, striafaciens and garcae are taxonomically redundant.