Pathovar Discrimination within Pseudomonas syringae subsp. savastanoi Using Whole Cell Fatty Acids and Pathogenicity as Criteria

Abstract

Fifty-two strains of the bacterium Pseudomonas syringae subsp. savastanoi from six different hosts were characterized by physiological, biochemical and pathogenicity tests and whole cell fatty acid analysis (FAA). Six other Pseudomonas strains were included for comparison in FAA. All 52 strains formed a very homogenous group on the basis of physiological and biochemical tests. On the basis of pathogenicity tests on 4 different hosts, strains could be divided into the three pathovars of P. syringae subsp. savastanoi formerly described, viz. pv. oleae, pv. nerii and pv. fraxini. This division into pathovars could be confirmed by FAA, thus showing that FAA is a supportive tool for taxonomic study below species level of plant pathogenic bacteria. Pv. fraxini strains (isolated from Fraxinus excelsior), formed a discrete cluster in principal component analysis. Pv. nerii strains (isolated from Nerium oleander) and pv. oleae strains (isolated from Olea europea, Jasminum sp., Ligustrum japonicum or Phillyrea sp.) could also be separated but showed close relationship. Two pv. fraxini strains showed a deviating (pv. oleae) fatty acid pattern. The fatty acids 11 : 0 iso 3OH, 20 : 0 and 20 : 1 trans 11 were found to be exclusively present in pv. nerii, but they were not present in all strains. Pathovar discriminative fatty acids were 16:0, 16:1 cis 9, 18 : 0, 18 : 1 cis 11 or the ratio of 16 : 1 cis 9/18 : 1 or 16 : 1 cis 9 + 16 : 0/18 : 1 + 12 : 0 2OH.