Taxonomy and epidemiology of Pectobacterium and Dickeya spp. in Europe, North America and South Africa

The blackleg-soft rot-aerial stem rot disease complex causes serious losses to the potato industry. It is caused by species of the genera Pectobacterium and Dickeya, collectively known as the soft rot Pectobacteriaceae. These soft rot Pectobacteriaceae also cause damage in a wide range of other host plants. Pectobacterium brasiliense has been the most prevalent in potato and pathogenic species in Europe and South Africa for the past decade, although the species composition is in constant flux due to the introduction of new species and taxonomic reclassification of current ones.

Updated information on the current species composition is required, as well as knowledge of possible differences in symptom expression between species. Such information would aid certification and diagnostic services in testing for the correct species and making accurate diagnoses.

Findings indicate that Pectobacterium brasiliense remains the most prevalent and widely distributed species in potato production areas. Other species that were identified included e.g. Pectobacterium carotovorum, Pectobacterium parmentieri, Dickeya chrysanthemi and Pectobacterium versatile. Pectobacterium brasiliense was also the most pathogenic species on potato. When looking at other host plants a wide variety of Pectobacterium and Dickeya species with large genetic variation occurs.

MALDI-TOF MS can only be used to identify Pectobacterium and Dickeya isolates at the genus level but preliminary results after improving the reference library look promising.

Given that there is also a large group of nonvirulent P. brasiliense isolates, a specific PCR which can differentiate between virulent and nonvirulent isolates of this species is being developed.