EMERGING THREATS TO THE KIWIFRUIT INDUSTRY Pectobacterium carotovorum subsp actinidiae subsp nov., a new bacterial pathogen causing canker-like symptoms in yellow kiwifruit, Actinidia chinensis

In this study, symptoms closely resembling those caused by Pseudomonas syringae pv. actinidiae were found in kiwifruit plants (Actinidia chinensis cv. Hort16A) growing in Jeju province, Korea. Bacterial strains including strain KKH3(T) were isolated from representative lesions on kiwifruit plants. Comparative 16S rRNA gene sequence-based phylogenetic analysis placed these bacteria in a separate cluster within the genus Pectobacterium. Strain KKH3(T) showed the highest similarity (98.7%) to the recognised bacteria Pectobacterium carotovorum subsp. carotovorum and Pectobacterium wasabiae. To justify subspecies level differentiation, the partial nucleotide sequences of atpD, carA and recA from strain KKH3(T) were compared with those from other members of the family Enterobacteriaceae. Distant relationships between strain KKH3(T) and six reference strains of Pectobacterium spp. were evident in the phylogenetic tree. The results of the DNA-DNA hybridisation and polyphasic analysis revealed that strain KKH3(T) belongs to another subspecies of P. carotovorum, for which the name Pectobacterium carotovorum subsp. actinidiae subsp. nov. is hereby proposed.