CLASSIFICATION OF PLANT PATHOGENIC PSEUDOMONADS BY GENETIC FINGERPRINTS DERIVED BY THE REPETITIVE EXTRAGENIC PALINDROMIC SEQUENCE POLYMERASE CHAIN REACTION (REP-PCR)
DE STEAD and J HENNESSY
Central Science Laboratory, Sand Hutton, York, Y04 1 LZ, UK
Background and objectives
Materials and methods
Results and conclusions
More than 100 clusters of strains were found. In addition many single strains gave unique fingerprints. Some species including P. ficuserectae, P. avellanae, P. amygdaii, P. corrugata, P. fuscovaginae and P. agarici were homogeneous. Others including P. syringae, P. savastanoi, P. cichorii, P. viridiflava, P. marginalis, P. caricapapayae, P. tolaasii, and P. fluorescens were heterogeneous. Within P. syringae, P. savastanoi and to a lesser extent, P. viridiflava and P. cichorii, clusters often correlated with host. Pathovar syringae was particularly heterogeneous although most lilac strains fell into one exclusive cluster. Several other pathovars could not be differentiated from each other. These included pathovars maculicola, tomato, apii and strains from magnoliae and rallistemon. Also, most strains of pathovars coronafaciens, atrofaciens, oryzae and agarcae, mostly from monocots, also clustered together and were not well differentiated from one another.
Pathovars which were well differentiated included delphinii, antirrhini, philadelphi, papulans, aptata, morsprunorum and lachrymans. Pathovar pisi comprised two discrete groups possibly correlated with race classification.In conclusion, REP-PCR derived genetic fingerprints have great potential value in the classification of this taxonomically difficult group. A revised pathovar-based classification may be appropriate, although at present we cannot use the fingerprints to assign strains to the genomic species proposed by Gardan et al .