Occurrence of Dickeya and Pectobacterium in Lake Water and the Rhizosphere of Waterside Plants Collected in the French Region La Dombes

Pectinolytic bacteria of the Pectobacteriaceae family constitute an important group of plant pathogens. Apart from infected plants, they are regularly found in aquatic environments. Pectinolytic isolates were selected, during 3 years, from water of naturally eutrophic lakes and from the rhizosphere of waterside plants in a site protected from direct agricultural inputs. A total of 89 isolates were assigned to Enterobacterales including the genera Dickeya (62%) and Pectobacterium (13%). In contrast to previous reports showing the prevalence of Pectobacterium species in river water, the Dickeya isolates were largely preponderant in lake water. Six Dickeya and four Pectobacterium species were isolated from water including D. oryzae, D. lacustris, D. parazeae, P. quasiaquaticum and P. aquaticum and, at a low frequency, D. chrysanthemi, D. aquatica, D. zeae, P. brasiliense, and P. versatile. The most common species isolated from plant rhizosphere was D. chrysanthemi. Notably, the rhizosphere of Solanum dulcamara harbored the highest number and diversity of Dickeya and Pectobacterium isolates. Members of different species and/or genera were found in the same water sample or plant rhizosphere, indicating that they can cohabit in close environments. Despite noticeable individual variations, the water strains have a pathogenic potential similar to that of other strains of the same species.