USE OF PROTEIN ELECTROPHORETOGRAMS FOR THE IDENTIFICATION OF RALSTONIA SOLANACEARUM IN POTATO TUBERS
Stefani E., Mazzucchi U.
U.C.I. Scienze e Tecnologie Agroalimentari e Agroambientali, University of Bologna, Italy
Densitometric analysis was performed on protein profiles of 55 strains of Ralstonia solanacearum from an international collection, isolated from different hosts and different geographical areas. The purpose was to set up a rapid and reliable method for the identification of this quarantine pathogen in potato lots imported from countries where the disease is endemic. Eighteen saprophytic potato strains were also isolated in Italy from imported potato lots, with morphological traits very similar to R. solanacearum and their protein profiles were compared with those of the pathogen. The comparison of all the electrophoretograms was made with an appropriate software, used to perform the principal component analysis (PCA) and calculate the correlation coefficient (Pearson index). This made it possible to discriminate very clearly between the saprophytes and all the pathogen strains, from potato and from other hosts. The R. solanacearum strains were divided into two groups: all the potato and some tomato strains (race 3) from the Mediterranean area were included in one group (group A). It was also possible to identify a group containing the Central America strains, while other groups included strains from other geographical areas, both isolated from potato and from other hosts. The correlation coefficient made it possible to group all the R. solanacearum strains for r=0.76; within this there was group A with r=0.92. A potato saprophytic strain was noted in association with some strains of the pathogen isolated in tropical areas: PCA only was useful to discriminate that strain; the other saprophytes had very low correlation indices, from 0.58 to 0.13. These results showed the taxonomic uniformity of R. solanacearum potato strains isolated in the European and Mediterranean area and the possibility of using the analysis of electrophoretograms to distinguish this pathogen from any saprophytic strains with very similar morphological features.
