Phenotypic and genotypic analysis of Pseudomonas syringae recovered from symptomatic beans and associated weeds in Northern Spain

Abstract

Thirty isolates of Pseudomonas syringae other than pathovar (pv.) phaseolicola, recovered from beans (18) and weeds (12) in a Northern Spanish region, were studied by a polyphasic approach, including phenotypic tests, detection of levansucrase and toxin (syringomycin and syringopeptin) genes, typing by RAPD (Random Amplified Polymorphic DNA) and PFGE (Pulsed-Field Gel Electrophoresis). The isolates were phenotypically heterogeneous, and both RAPD and PFGE, probed to be highly discriminative, as they were almost able to differentiate at the level of isolate. Phylogenetic analysis based on conserved genes of the core genome (rpoD, gltA and gyrB) distributed the isolates in three different clades (2A, 2B and 2C) belonging to phylogroup 2 of the P. syringae complex. According to toxin production, 18 of them, within clade 2B, were assigned to P. syringae pv. syringae and five of these caused symptoms after experimental inoculation on bean pods. Four of the five pathogenic isolates were obtained from weeds, supporting the role of weeds associated with bean crops, particularly Cyperus rotundus, Malva sylvestris, and Polygonum lapathifolium, as a reservoir of the pathogen. In conclusion, results of this study suggest that apart from P. syringae pv. phaseolicola, P. syringae isolates circulating in our region are mostly epiphytes, and support the role of weeds associated with bean crops as reservoir of pathogenic strains of P. syringae pv. syringae.