Infection by a coronatine-producing strain of Pectobacterium cacticidum isolated from sunflower plants in Mexico is characterized by soft rot and chlorosis

A novel strain of Pectobacterium, isolated from infected sunflower plants (Helianthus annuus L.) in Mexico was characterized. Inoculated sunflower plants developed both tissue chlorosis and soft-rot on leaves. The broad host range shown by this pathogen, which included members of the Agavaceae, Asteraceae, Brassicaceae and Solanaceae, was characteristic of the genus Pectobacterium. The metabolic profile and molecular data, in addition to the secretion of plant-cell-wall-degrading enzymes, confirmed its identification as a member of the Pectobacterium genus. A phylogenetic tree constructed on the basis of its 16S rDNA sequence revealed a high identity (98 %) with P. cacticidum. Amplification and restriction-fragment-length-polymorphism analysis of internal transcribed sequences further confirmed its classification as P. cacticidum. Similar to strains of P. atrosepticum, P. carotovorum and Dickeya spp., the new P. cacticidum strain FHLGJ22 has a coronafacic ligase gene and produces coronatine, a virulence factor usually associated with phytopathogenic strains of Pseudomonas syringae. Our results suggest that this strain may utilize a dual infection process involving cell maceration and plant toxins, which is synchronized via an unknown mechanism, might confer an adaptive advantage to colonize different plant hosts.